Parkinson's Disease

Complex MONDO:0005180 Pathograph 87 Show in embeddings browser Neurodegenerative Disease Movement Disorder

Parkinson's disease is a progressive neurodegenerative movement disorder caused by the loss of dopaminergic neurons in the substantia nigra pars compacta, producing striatal dopamine deficiency and basal ganglia circuit dysfunction. It manifests as bradykinesia, resting tremor, rigidity, and postural instability, with non-motor features. The pathological hallmark is intraneuronal aggregation of misfolded alpha-synuclein (Lewy bodies), with mitochondrial dysfunction and oxidative stress contributing to neurodegeneration.

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Mappings

MONDO

MONDO:0008199 late-onset Parkinson disease Not Yet Curated

MONDO:0008199 (late-onset Parkinson disease, OMIM:168600, "PARK"/"LOPD"; onset after ~age 50) is the common sporadic/idiopathic adult-onset form and a child of MONDO:0005180. This entry curates Parkinson disease at the broad MONDO:0005180 level, and its pathophysiology (α-synucleinopathy and dopaminergic neurodegeneration, SNCA/LRRK2/GBA1) substantively covers the late-onset form. Recorded as a narrowMatch so coverage tooling resolves MONDO:0008199 to this entry rather than flagging it as uncurated.

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Subtypes

SNCA-associated Parkinson disease (PARK1) MONDO:0008200

SNCA hgnc:11138

Autosomal-dominant Parkinson disease caused by a mutation in SNCA. The mutation was identified in a large Italian kindred and in three unrelated families of Greek origin with autosomal dominant inheritance, and was the finding that established alpha-synuclein as a Mendelian cause of the disease. MONDO's separate PARK4 term covers the SNCA locus multiplications; see that row for the distinction.

Show evidence (1 reference)

PMID:9197268 SUPPORT Human clinical

"A mutation was identified in the alpha-synuclein gene, which codes for a presynaptic protein thought to be involved in neuronal plasticity, in the Italian kindred and in three unrelated families of Greek origin with autosomal dominant inheritance for the PD phenotype."

Establishes SNCA point mutation as a dominant Mendelian cause of Parkinson disease, the entity MONDO labels PARK1.

SNCA multiplication Parkinson disease (PARK4) MONDO:0011562

SNCA hgnc:11138

Autosomal-dominant Parkinson disease caused by duplication or triplication of the SNCA locus rather than by a coding change, so the mechanism is increased wild-type alpha-synuclein gene dosage. Clinical severity tracks copy number. HGNC records PARK1 and PARK4 as previous symbols of SNCA, so the two MONDO terms are one gene distinguished by allelic mechanism, not two loci.

Show evidence (2 references)

PMID:18571778 SUPPORT Human clinical

"SNCA dosage is responsible for parkinsonism, autonomic dysfunction, and dementia observed within each family."

Attributes the phenotype in five multiplication families to SNCA copy number, which is the defining mechanism of this subtype.

PMID:18571778 SUPPORT Human clinical

"The severity of clinical presentation is correlated with SNCA dosage and does not appear to be overtly affected by the presence of other genes in the multiplicated region."

Supports the dose-severity relationship and excludes neighbouring genes in the duplicated interval as the driver.

PINK1 early-onset Parkinson disease (PARK6) MONDO:0011613

PINK1 hgnc:14581

Autosomal-recessive early-onset Parkinson disease caused by biallelic PINK1 variants affecting the kinase domain. PINK1 is mitochondrially located, and its loss links the subtype to the mitochondrial quality-control arm of the pathograph.

Show evidence (2 references)

PMID:15087508 SUPPORT Human clinical

"Here we show that mutations in PINK1 (PTEN-induced kinase 1) are associated with PARK6."

Identifies PINK1 as the gene at the PARK6 locus, which is the MONDO term bound here.

PMID:15087508 SUPPORT In vitro / ex vivo

"Cell culture studies suggest that PINK1 is mitochondrially located and may exert a protective effect on the cell that is abrogated by the mutations, resulting in increased susceptibility to cellular stress."

Supports the mitochondrial localization and loss-of-protection mechanism that places this subtype on the mitochondrial dysfunction node.

FBXO7 parkinsonian-pyramidal syndrome (PARK15) MONDO:0009830

FBXO7 hgnc:13586

Autosomal-recessive early-onset parkinsonism combined with pyramidal tract signs, caused by biallelic FBXO7 variants. Its defining feature is that combination of early-onset progressive parkinsonism with pyramidal tract involvement, which is the phenotype the discovery study delineated as PARK15.

Show evidence (2 references)

PMID:19038853 SUPPORT Human clinical

"We conclusively show that recessive FBXO7 mutations cause progressive neurodegeneration with extrapyramidal and pyramidal system involvement, delineating a novel genetically defined entity that we propose to designate as PARK15."

Establishes FBXO7 as the cause of the parkinsonian-pyramidal entity MONDO binds here, and names it PARK15.

PMID:19038853 SUPPORT Human clinical

"An FBXO7 homozygous truncating mutation (Arg498Stop) was found in an Italian family, while compound heterozygous mutations (a splice-site IVS7 + 1G/T mutation and a missense Thr22Met mutation) were present in a Dutch family."

Documents the biallelic FBXO7 genotypes in the two families, supporting recessive inheritance for this subtype.

VPS35 late-onset Parkinson disease (PARK17) MONDO:0013625

VPS35 hgnc:13487

Autosomal-dominant late-onset Parkinson disease caused by the recurrent VPS35 p.Asp620Asn variant. VPS35 is a component of the retromer complex. Penetrance is high but incomplete, and mean age of onset in the affected individuals of the discovery families was 53 years.

Show evidence (3 references)

PMID:21763483 SUPPORT Human clinical

"We found a missense mutation, c.1858G>A (p.Asp620Asn), in the VPS35 gene in all seven affected family members who are alive."

Identifies the recurrent VPS35 variant that defines this subtype.

PMID:21763483 SUPPORT Human clinical

"By screening additional PD cases, we saw the same variant cosegregating with the disease in an autosomal-dominant mode with high but incomplete penetrance in two further families with five and ten affected members, respectively."

Supports autosomal-dominant transmission with reduced penetrance in two replication families.

PMID:21763483 SUPPORT Human clinical

"The mean age of onset in the affected individuals was 53 years."

Source for the age of onset stated in this subtype description.

DNAJC6 juvenile parkinsonism (PARK19A) MONDO:0014231

DNAJC6 hgnc:15469

Autosomal-recessive juvenile parkinsonism caused by a DNAJC6 variant identified by homozygosity mapping. DNAJC6 encodes auxilin, the neuron-specific clathrin-uncoating co-chaperone, so the subtype sits on the synaptic-vesicle recycling arm of the pathograph rather than the mitochondrial one. Parkinsonism is usually not the presenting feature: developmental delay, intellectual disability, seizures, other movement disorders and neuropsychiatric features occur in the majority of juvenile-onset individuals and often precede it. In the two siblings of the PMID:42414182 case series, levodopa gave only mild benefit and dose escalation provoked an adverse motor reaction.

Show evidence (5 references)

PMID:42414182 SUPPORT PRIMARY RESULT Human clinical

"Both patients exhibited developmental regression, parkinsonism with dystonia, cognitive decline, dysphagia, and marked sialorrhea, with severe, accelerated functional deterioration."

Describes the juvenile phenotype in the two siblings (aged 17 and 14), including developmental regression and rapid functional decline.

PMID:42414182 SUPPORT PRIMARY RESULT Human clinical

"Levodopa produced only mild benefit; in the older sibling, dose escalation provoked an adverse reaction with sustained upgaze/ophthalmoparesis, opisthotonus, and hypertension."

Reports poor levodopa response and a dose-related adverse reaction in the older sibling; the treatment-response sentence in this subtype's description rests on it.

PMID:22563501 SUPPORT Human clinical

"Using homozygosity mapping and whole exome sequencing we identified a deleterious mutation in DNAJC6 in two patients with juvenile parkinsonism."

Identifies DNAJC6 in juvenile parkinsonism, the phenotype MONDO files as PARK19A.

+ 2 more references

DNAJC6 early-onset Parkinson disease (PARK19B) MONDO:0800369

DNAJC6 hgnc:15469

Autosomal-recessive early-onset Parkinson disease caused by homozygous DNAJC6 variants, with onset in the third to fifth decade and slow progression. It is the milder end of the DNAJC6 spectrum and is separated from PARK19A by onset and course rather than by gene.

Show evidence (3 references)

PMID:26528954 SUPPORT Human clinical

"We identified two families with different novel homozygous DNAJC6 mutations segregating with PD."

Reports biallelic DNAJC6 variants segregating in two early-onset PD families.

PMID:33983693 SUPPORT REVIEW SYNTHESIS Human clinical

"A minority of individuals with DNAJC6 Parkinson disease develop early-onset parkinsonism with symptom onset in the third to fourth decade and absence of additional neurologic features."

The basis for separating this row from PARK19A: a minority present with parkinsonism alone and later onset. The chapter gives the window as the third to fourth decade where PMID:26528954 reports third to fifth; both are kept rather than reconciled, since they are different case series.

PMID:26528954 SUPPORT Human clinical

"All these cases fulfilled the criteria for a clinical diagnosis of early-onset PD, had symptoms onset in the third-to-fifth decade, and slow disease progression."

Source for the onset window and slow course that distinguish this subtype from the juvenile DNAJC6 form.

SYNJ1 early-onset parkinsonism (PARK20) MONDO:0014233

SYNJ1 hgnc:11503

Autosomal-recessive early-onset parkinsonism with dystonia and cognitive deterioration, caused by biallelic SYNJ1 variants. Synaptojanin 1 is a phosphoinositide phosphatase required for postendocytic synaptic-vesicle recycling, placing this subtype alongside the DNAJC6 forms. Levodopa response was poor in the index family.

Show evidence (2 references)

PMID:23804577 SUPPORT Human clinical

"we report the identification, by homozygosity mapping and exome sequencing, of a SYNJ1 homozygous mutation (p.Arg258Gln) segregating with disease in an Italian consanguineous family with Parkinsonism, dystonia, and cognitive deterioration."

Identifies the biallelic SYNJ1 variant and the phenotype that defines this subtype.

PMID:23804577 SUPPORT Human clinical

"Response to levodopa was poor, and limited by side effects."

Source for the poor levodopa response stated in this subtype description.

CHCHD2 late-onset Parkinson disease (PARK22) MONDO:0014742

CHCHD2 hgnc:21645

Late-onset Parkinson disease segregating as an autosomal-dominant trait in Japanese families with CHCHD2 variants. The evidence is weaker than for the other dominant loci curated here: the discovery study found three variants in four of 341 autosomal-dominant index cases and stated that its own finding needed confirmation in other populations, and the ClinGen Gene-Disease Validity table lists no CHCHD2-Parkinson disease assertion (checked 2026-09-25).

Show evidence (2 references)

PMID:25662902 SUPPORT Human clinical

"Three CHCHD2 mutations in four of 341 index cases from independent families with autosomal dominant Parkinson's disease were detected by CHCHD2 mutation screening"

Gives the yield behind the CHCHD2-PD claim in the discovery cohort.

PMID:25662902 SUPPORT Human clinical

"CHCHD2 mutations are associated with, and might be a cause of, autosomal dominant Parkinson's disease."

The authors' own hedged conclusion, quoted to keep this subtype's confidence level explicit rather than asserting an established Mendelian locus.

VPS13C early-onset Parkinson disease (PARK23) MONDO:0014796

VPS13C hgnc:23594

Autosomal-recessive early-onset parkinsonism caused by biallelic truncating VPS13C variants, with rapid severe progression and early cognitive decline. VPS13C loss lowers mitochondrial membrane potential and increases PINK1/parkin-dependent mitophagy, which is why this subtype is wired to the mitochondrial dysfunction node.

Show evidence (2 references)

PMID:26942284 SUPPORT Human clinical

"This work suggests that loss of function of VPS13C is a cause of autosomal-recessive early-onset parkinsonism with a distinctive phenotype of rapid and severe progression."

Establishes biallelic VPS13C loss of function as a cause of recessive early-onset parkinsonism.

PMID:26942284 SUPPORT Human clinical

"VPS13C mutations are associated with a distinct form of early-onset parkinsonism characterized by rapid and severe disease progression and early cognitive decline"

Source for the rapid progression and early cognitive decline stated in this subtype description.

PTPA early-onset parkinsonism with intellectual disability (PARK25) MONDO:0957576

PTPA hgnc:9308

Autosomal-recessive early-onset parkinsonism accompanied by intellectual disability, caused by biallelic missense PTPA variants that impair activation of the PP2A phosphatase. Motor symptoms in the reported families responded to levodopa and to subthalamic deep brain stimulation.

Show evidence (3 references)

PMID:36073231 SUPPORT Human clinical

"We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability."

Establishes the gene, inheritance mode and combined motor plus cognitive phenotype that define this subtype.

PMID:36073231 SUPPORT Human clinical

"The affected subjects display juvenile-onset parkinsonism and intellectual disability."

Describes the phenotype in the two discovery families.

PMID:37046398 SUPPORT Human clinical

"One patient with early-onset PD from a consanguineous family carried the homozygous variant p.Met329Val, while her parents and elder sister with heterozygous p.Met329Val were healthy."

Independent replication in a third consanguineous family, with unaffected heterozygous relatives supporting recessive inheritance.

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Mechanistic Hypotheses

Canonical α-Synucleinopathy and Dopaminergic Neurodegeneration Model

canonical_synucleinopathy_dopaminergic_neurodegeneration_model CANONICAL

Evidence balance 1 support

Misfolded α-synuclein aggregates into oligomers and Lewy bodies, propagates trans-synaptically in a prion-like manner, and induces progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta. The resulting striatal dopamine deficiency causes the cardinal motor signs (bradykinesia, rigidity, tremor, postural instability), while broader Lewy pathology in autonomic, brainstem, and cortical regions accounts for the non-motor symptoms (REM-sleep behavior disorder, hyposmia, constipation, cognitive impairment). Pathway evidence implicates impaired autophagy/lysosomal clearance (GBA), mitochondrial dysfunction (PINK1/Parkin), and oxidative stress as upstream amplifiers; loss of dopaminergic feedback to the indirect/direct basal ganglia circuits explains the motor circuit signature.

Retained as CANONICAL. The 2026 falcon hypothesis-search report (kb/hypotheses/Parkinsons_Disease/canonical_synucleinopathy_dopaminergic_neurodegeneration_model; openscientist timed out) confirms misfolded α-synuclein aggregation, Lewy-body formation, and progressive substantia-nigra pars-compacta dopaminergic neuron loss as the central mechanism. Three qualifications: (1) the prion-like cell-to-cell propagation model is well-validated in mouse and primate models (intracerebral PFF injection seeds endogenous aggregates and produces motor deficits), but its rate-limiting role in human sporadic PD remains debated; (2) GBA1 heterozygosity, mitochondrial dysfunction (PINK1/Parkin), impaired autophagy/lysosomal clearance, and gut-brain axis (vagal Lewy pathology, microbiome) are increasingly recognized upstream amplifiers — particularly the gut-first Braak hypothesis, supported by hyposmia and REM-sleep behavior disorder preceding motor symptoms by 10-20 years; (3) LRRK2 G2019S and other genetic PD subtypes display Lewy-pathology variability, indicating molecular heterogeneity within the unified clinical syndrome. Anti-α-synuclein immunotherapies (prasinezumab, cinpanemab) have shown target engagement but limited clinical efficacy, suggesting aggregation may be a downstream marker rather than the rate-limiting therapeutic target.

Deep research

Falcon citations 56 citations 2026-05-23T19:21:21.440028

Show evidence (1 reference)

PMID:37048085 SUPPORT Human clinical

"dopaminergic neuronal loss in substantia nigra pars compacta of the brain and aggregation of intracellular protein α-synuclein are the pathological characterizations"

Canonical mechanism review used as the seed reference for the hypothesis-search deep-research run.

Body-First Enteric α-Synuclein Initiation Model

body_first_enteric_alpha_synuclein_model ALTERNATIVE

Evidence balance 10 support 1 refute

Alpha-synuclein pathology initiates in the enteric nervous system or other peripheral autonomic sites, then propagates through vagal connections to the dorsal motor nucleus and broader brainstem before joining the central alpha-synuclein propagation and dopaminergic-neurodegeneration cascade. This model best explains Parkinson disease presentations with early constipation, REM-sleep behavior disorder, autonomic dysfunction, and early peripheral/cardiac sympathetic denervation.

Evidence is strongest for the gut-to-brain propagation route in animal models where truncal vagotomy or alpha-synuclein deficiency blocks spread. Human clinical and imaging studies support a body-first subtype pattern, but microbiome dysbiosis and enteric seeding remain unresolved as causal triggers versus modifiers or consequences. The consequence reading now has a curated counterpart: Striatal Dopamine Deficiency carries a downstream edge to Gut Microbiome Dysbiosis, sourced to a rat nigrostriatal lesion that shifts gram-negative bacterial classes and lowers short-chain fatty acids. That edge is deliberately not tagged to this hypothesis group, because it describes a consequence of established dopaminergic loss rather than the origin site of alpha-synuclein pathology. The 2026 OpenScientist hypothesis-search report (kb/hypotheses/Parkinsons_Disease/body_first_enteric_alpha_synuclein_model) judges this model PARTIALLY SUPPORTED and recommends retaining ALTERNATIVE status: it is one well-supported origin-site pathway (an estimated ~20-30% of PD) within the multi-origin Synuclein Origin and Connectome (SOC) framework, not a universal disease mechanism. Convergent support spans mouse gut-to-brain transmission (vagotomy and α-syn knockout each block spread), human truncal-vagotomy epidemiology (reduced PD risk at long follow-up), gut-microbiota dependence in α-syn-overexpressing mice, and a distinct body-first clinical-imaging signature (more symmetric nigrostriatal degeneration, early cardiac sympathetic denervation). Key qualifications: (1) the upstream trigger for enteric α-syn misfolding is unknown; (2) enteric α-syn immunohistochemistry lacks diagnostic specificity (positive also in controls); (3) LRRK2-associated PD is frequently α-syn seed amplification assay (SAA)-negative, showing α-syn-independent parkinsonian pathways; (4) 6-43% of cases deviate from caudo-rostral Braak staging, iRBD prodrome is heterogeneous, FMT trials are inconsistent, and anti-α-syn immunotherapies have failed in established PD.

Pathograph links

Gut Microbiome Dysbiosis -> Intestinal Inflammation and Barrier Dysfunction INDIRECT UNKNOWN INTERMEDIATES PD-associated dysbiosis may promote a pro-inflammatory intestinal state and barrier dysfunction, but the direction and necessity of this link remain unresolved in humans.

Intestinal Inflammation and Barrier Dysfunction -> Enteric Alpha-Synuclein Seeding INDIRECT UNKNOWN INTERMEDIATES Local gut inflammation and barrier leakiness may increase enteric alpha-synuclein expression or amyloidogenic exposure, providing a permissive setting for enteric alpha-synuclein seeding.

Enteric Alpha-Synuclein Seeding -> Vagal-Brainstem Alpha-Synuclein Propagation DIRECT Enteric alpha-synuclein seeds can propagate first to vagal brainstem nuclei and then to additional brain regions.

Enteric Alpha-Synuclein Seeding -> Constipation UNKNOWN Enteric or autonomic involvement is a plausible contributor to early constipation in body-first PD, but this edge remains clinically inferred.

Vagal-Brainstem Alpha-Synuclein Propagation -> Alpha-Synuclein Aggregation INDIRECT KNOWN INTERMEDIATES Vagal-brainstem propagation links gut-origin pathology to the broader central alpha-synuclein aggregation cascade. Intermediates: dorsal motor nucleus and nucleus tractus solitarius involvement; caudal hindbrain and higher brain region propagation

Vagal-Brainstem Alpha-Synuclein Propagation -> Pontine Tegmental Alpha-Synuclein Pathology DIRECT As vagal-brainstem propagation continues rostrally, the pontine tegmentum - the site of the REM-atonia-generating circuit - is reached ahead of the nigrostriatal and cortical structures that define overt motor and cognitive disease.

Pontine Tegmental Alpha-Synuclein Pathology -> Loss of Descending Drive to Inhibitory Premotor Neurons DIRECT Pathology involving the pontine REM-on glutamatergic population removes the excitatory drive its descending axons carry to medullary and spinal inhibitory premotor neurons.

Loss of Descending Drive to Inhibitory Premotor Neurons -> REM Sleep Muscle Atonia Loss DIRECT Without descending excitation of the inhibitory premotor pool, skeletal motor neurons are not hyperpolarised during REM sleep and muscle tone persists.

Deep research

OpenScientist citations 42 citations 2026-07-06T10:39:19.549709

Show evidence (11 references)

PMID:38519273 SUPPORT Human clinical

"the initial pathology starts either in the olfactory bulb or amygdala leading to a brain-first subtype, or in the enteric nervous system leading to a body-first subtype."

Recent review-level synthesis of human imaging, clinical, and pathology studies explicitly frames enteric-origin body-first PD as an alternative subtype within the ASOC model.

PMID:31255487 SUPPORT Model organism

"Truncal vagotomy and α-syn deficiency prevented the gut-to-brain spread of α-synucleinopathy and associated neurodegeneration and behavioral deficits."

Mouse gut-to-brain transmission experiments support the vagus nerve and alpha-synuclein as required components of the body-first propagation route.

PMID:39241780 SUPPORT Model organism

"Truncal vagotomy and α-Syn deficiency significantly inhibited synucleinopathy or tauopathy spreading."

Gut-inducible mouse models provide independent support that vagotomy and alpha-synuclein deficiency inhibit gut-origin propagation into the brain.

+ 8 more references

Brain-First Central α-Synuclein Initiation Model

brain_first_central_alpha_synuclein_model ALTERNATIVE

Evidence balance 9 support 1 refute

Alpha-synuclein pathology initiates within central nervous system sites such as the olfactory bulb or amygdala and spreads centrifugally to brainstem and peripheral autonomic structures. This model best explains Parkinson disease presentations where central dopaminergic or olfactory involvement precedes prominent autonomic and enteric manifestations.

The model is supported mainly by subtype-level human imaging, clinical, and neuropathological patterns. It competes with, rather than refutes, the body-first model because both origin routes may exist within clinically diagnosed Parkinson disease. The 2026 OpenScientist hypothesis-search report (kb/hypotheses/Parkinsons_Disease/brain_first_central_alpha_synuclein_model) judges this model PARTIALLY SUPPORTED and recommends retaining ALTERNATIVE status. Supporting evidence is convergent at the subtype level: large-scale neuropathological trajectory modelling (81.9% of Lewy-body donors have earliest pathology in the olfactory bulb), multimodal imaging showing asymmetric central dopaminergic loss preceding peripheral autonomic denervation in RBD-negative PD, and primate/mouse olfactory-bulb PFF injection reproducing olfactory-to-limbic-to-brainstem spread. Key qualifications: (1) no prospective longitudinal human study has tracked α-syn pathology from a CNS origin outward; (2) RBD as a body-first proxy is unreliable (PSG-confirmed prevalence 17.8-62.5% by ascertainment); (3) structural MRI is conflicting - a 255-patient PPMI cohort found no gray matter volume asymmetry difference between putative subtypes; (4) dermal SAA cannot differentiate subtypes in established disease and origin-site is not yet integrated into NSD-ISS/SynNeurGe biological staging; (5) α-syn strain differences that might determine origin route remain uncharacterized between subtypes.

Pathograph links

Central Alpha-Synuclein Initiation -> Alpha-Synuclein Aggregation INDIRECT KNOWN INTERMEDIATES Central initiation feeds into the broader alpha-synuclein aggregation and propagation cascade through connected brain networks. Intermediates: central network propagation from olfactory bulb or amygdala

Deep research

OpenScientist citations 36 citations 2026-07-06T06:14:58.676310

Show evidence (10 references)

PMID:38519273 SUPPORT Human clinical

"the initial pathology starts either in the olfactory bulb or amygdala leading to a brain-first subtype, or in the enteric nervous system leading to a body-first subtype."

The ASOC model explicitly defines an olfactory bulb/amygdala origin as the brain-first subtype that competes with the enteric body-first route.

PMID:38519273 SUPPORT Human clinical

"These subtypes should be distinguishable early in the disease course on a range of imaging, clinical, and neuropathological markers."

Human subtype distinguishability supports representing brain-first and body-first disease routes as alternative mechanistic hypothesis groups.

PMID:32830221 SUPPORT Human clinical

"the PDRBD- data were compatible with a brain-first trajectory, characterized by primary loss of putaminal FDOPA uptake followed by a secondary loss of cardiac MIBG signal and 11C-donepezil signal."

Primary multimodal imaging data support a brain-first trajectory in RBD-negative de novo PD, where central dopaminergic dysfunction appears before peripheral autonomic marker loss.

+ 7 more references

Synaptic Vesicle Endocytosis Dysfunction as a Convergent PD Mechanism

synaptic_vesicle_endocytosis_convergence EMERGING

Evidence balance 2 support

A growing set of PD genes act in synaptic vesicle recycling and clathrin-mediated endocytosis rather than in alpha-synuclein handling directly: SYNJ1, DNAJC6, SH3GL2, LRRK2, VPS35, and now ITSN1. This hypothesis holds that disrupted presynaptic vesicle endocytosis is a convergence point that predisposes to PD, upstream of or parallel to alpha-synuclein aggregation, and that it is an early feature preceding overt neurodegeneration. ITSN1 is the newest entrant: rare protein-truncating variants carry a large odds ratio, and the fly ortholog interacts genetically and physically with alpha-synuclein. Open: whether the endocytic defect acts mainly by mishandling alpha-synuclein or by an independent route, and whether ITSN1's effect is specific to PD given its separate association with autism.

Seeded from the ITSN1 lead (Impetus Grants, Ryan Dhindsa). The Synaptic Dysfunction pathophysiology node already carries DNAJC6, SYNJ1 and ITSN1. An OpenScientist run was commissioned on this group to test whether the vesicle-endocytosis convergence is supported beyond the ITSN1 discovery paper; its assessment will be added separately.

Pathograph links

Synaptic Dysfunction -> Dopaminergic Neuron Loss

Synaptic Dysfunction -> Alpha-Synuclein Aggregation

Deep research

OpenScientist citations 13 citations 2026-10-18T05:48:18.032597

Show evidence (2 references)

PMID:40056900 SUPPORT Human clinical

"This study adds to the growing evidence that vesicle trafficking dysfunction is a key driver in PD pathogenesis."

The ITSN1 discovery paper frames its own finding as part of a vesicle-trafficking convergence, the claim this hypothesis groups.

PMID:40056900 SUPPORT Human clinical

"Interestingly, ITSN1 appears to interact with Synaptojanin-1 (SYNJ1), which is associated with early-onset PD."

Places ITSN1 in the same endocytic pathway as an established PD gene, supporting convergence rather than an isolated locus.

Discussions and Knowledge Gaps

Does restoring PGC-1alpha signaling protect nigral dopaminergic neurons in human Parkinson disease, given that rescue is seen in cellular models while sustained supraphysiological expression in the adult rat nigrostriatal system is itself dopaminergic-toxic?

HUMAN MODEL MISMATCH OPEN pd_pgc1a_therapeutic_window

Attached to

pathophysiology#PGC-1alpha Transcriptional Program Repression pathophysiology#Mitochondrial Dysfunction

The direction of the human observation is not in doubt: PGC-1alpha-responsive bioenergetic genes are underexpressed in laser-captured human nigral neurons early in disease, and the repressor PARIS accumulates in human Parkinson disease brain. What does not transfer cleanly from model to patient is the therapeutic inverse. Cellular models show that activating PGC-1alpha blocks alpha-synuclein- and rotenone-induced dopaminergic loss, but AAV-mediated sustained overexpression in the adult rat nigrostriatal system selectively impairs dopaminergic function and, at higher levels, causes overt degeneration - and it does not rescue alpha-synuclein-induced degeneration. PGC-1alpha therefore behaves as a rheostat with an activation-level, cell-type, isoform and disease-stage dependence rather than as a monotonic neuroprotective switch, so a positive result in one model system cannot be read as evidence that pathway activation is protective in patients. Recording this as a HUMAN_MODEL_MISMATCH rather than a plain KNOWLEDGE_GAP is deliberate: the model evidence exists and is abundant on both sides; it is its translational validity, and specifically the existence and width of a therapeutic window, that is unresolved. This gap is shared with other neurodegenerative entries (Huntington disease, Alzheimer disease, amyotrophic lateral sclerosis) in which the same coactivator is implicated.

Proposed experiments

Dose-graded PGC-1alpha activation in nigrostriatal models

dose-response perturbation study

exp_pd_pgc1a_dose_response_nigrostriatal

Titrate PGC-1alpha activity across a graded range - from partial restoration toward physiological levels up to the supraphysiological levels used in the AAV overexpression studies - in human iPSC-derived midbrain dopaminergic neurons and in an in vivo nigrostriatal model, reading out respiratory-chain subunit expression, mitochondrial membrane potential, dopamine content and dopaminergic survival at each level.

Decision criterion

A therapeutic window exists if there is a contiguous range of PGC-1alpha activity in which bioenergetic readouts improve without loss of dopaminergic markers or dopamine content; the rheostat model predicts an inverted-U with toxicity at the high end, whereas a simple neuroprotective model predicts monotonic benefit.

Human target-engagement biomarker for PGC-1alpha modulation

biomarker validation study

exp_pd_pgc1a_target_engagement_biomarker

Establish and validate a measurable readout of PGC-1alpha pathway engagement in living patients - for example a peripheral or CSF transcriptional signature of the PGC-1alpha-responsive gene set benchmarked against the postmortem nigral signature - so that a trial of any PGC-1alpha-directed agent can distinguish target-engagement failure from mechanism failure.

Decision criterion

The biomarker is usable if it shifts dose-dependently with a known PGC-1alpha modulator and correlates with the nigral PGC-1alpha-responsive gene-set deficit; absent such a readout, a negative clinical trial cannot be interpreted as refuting the mechanism.

Raised from dismech issue #6114 ([kgap-scan:scope] PGC-1alpha-mediated neuroprotection), which asked whether the Parkinson, Alzheimer and amyotrophic lateral sclerosis entries should carry a PGC-1alpha node. The Huntington disease entry already curates the mHTT-driven PGC-1alpha repression chain; Alzheimer disease and amyotrophic lateral sclerosis remain uncurated for this mechanism.

Show evidence (3 references)

PMID:22246294 SUPPORT Model organism

"In the adult rat nigrostriatal system, adeno-associated virus (AAV)-mediated overexpression of PGC-1α induces the selective loss of dopaminergic markers and increases dopamine (DA) catabolism, leading to a reduction in striatal DA content."

The in vivo counterexample to the cellular rescue result: sustained pathway activation is itself dopaminergic-toxic, which is what creates the translational uncertainty.

PMID:22246294 SUPPORT Model organism

"These results highlight the central role of PGC-1α in the function and survival of dopaminergic neurons and the critical need for maintaining physiological levels of PGC-1α activity."

States the therapeutic-window requirement directly - benefit is conditional on activity level, not on activation per se.

PMID:42430091 SUPPORT Other

"These observations suggest that PGC-1α is not a simple neuroprotective switch, but a flexible regulatory hub whose therapeutic value depends on cell type, isoform profile, disease stage, and activation level."

Cross-disease review framing that generalizes the mismatch beyond Parkinson disease and names the four context variables that determine whether modulation helps.

In body-first Parkinson disease, are gut microbiome dysbiosis and intestinal barrier/inflammatory changes causal triggers for enteric alpha-synuclein seeding, modifiers that amplify an already initiated synucleinopathy, or secondary consequences of autonomic gut dysfunction?

KNOWLEDGE GAP OPEN gap_pd_microbiome_causal_direction_body_first

Attached to

pathophysiology#Gut Microbiome Dysbiosis pathophysiology#Intestinal Inflammation and Barrier Dysfunction pathophysiology#Enteric Alpha-Synuclein Seeding pathophysiology#Vagal-Brainstem Alpha-Synuclein Propagation

Cross-sectional human studies support PD-associated dysbiosis and elevated intestinal inflammatory/permeability markers, while animal studies support gut-to-brain alpha-synuclein propagation through the vagus nerve. The unresolved step is temporal and causal: whether dysbiosis or barrier dysfunction initiates enteric alpha-synuclein misfolding in humans, merely accelerates propagation, or appears after autonomic denervation has already altered gut physiology.

Proposed experiments

Prodromal microbiome-barrier alpha-synuclein longitudinal cohort

longitudinal prodromal multi-omics cohort study

exp_pd_prodromal_microbiome_barrier_alpha_syn_longitudinal_cohort

Follow iRBD-, constipation-, and hyposmia-enriched prodromal cohorts with serial stool metagenomics, SCFA/metabolite profiling, fecal and serum calprotectin/zonulin, autonomic imaging, and standardized enteric alpha-synuclein biopsy assays before motor conversion.

Readouts

Microbiome dysbiosis trajectory

pathophysiology#Gut Microbiome Dysbiosis

Determine whether reproducible microbiome shifts precede, track with, or follow enteric alpha-synuclein and autonomic biomarker changes.

shotgun metagenomic sequencing fecal metabolomics

Direction: POSITIVE

Intestinal inflammation and barrier trajectory

pathophysiology#Intestinal Inflammation and Barrier Dysfunction

Measure whether inflammatory and permeability markers rise before enteric alpha-synuclein detection and clinical conversion.

calprotectin assay zonulin assay

Direction: POSITIVE

Enteric alpha-synuclein seeding

pathophysiology#Enteric Alpha-Synuclein Seeding

Track phosphorylated or aggregated alpha-synuclein in standardized enteric biopsies as a candidate initiating event.

immunohistochemistry alpha-synuclein seed amplification assay

Direction: POSITIVE

Decision criterion

Microbiome and barrier changes would support a trigger model only if they reproducibly precede enteric alpha-synuclein positivity and autonomic denervation in converters; changes that follow autonomic dysfunction would support a consequence or modifier model.

Would support

pathophysiology#Gut Microbiome Dysbiosis pathophysiology#Intestinal Inflammation and Barrier Dysfunction pathophysiology#Enteric Alpha-Synuclein Seeding

Show evidence (4 references)

PMID:34220443 SUPPORT Human clinical

"A causal relationship has not been established, but gut dysbiosis is prevalent in PD and may lead to intestinal inflammation and barrier dysfunction."

The human marker study states the core causal-direction uncertainty motivating this knowledge gap.

PMID:36332796 SUPPORT Other

"However, it remains unclear how these mechanisms relate to sporadic PD, a more common form of PD."

Review-level synthesis highlights uncertainty about how gut-related mechanisms map onto sporadic PD pathogenesis.

PMID:41826284 SUPPORT Human clinical

"Microbiome profiling revealed greater similarity to donor composition and a marked reduction in Escherichia-Shigella, correlating with decreased colonic α-synuclein aggregation"

The strongest interventional human evidence bearing on this gap: in a 72-patient phase 2 trial of repeated donor fecal transplantation the induced microbiome shift correlated with reduced colonic alpha-synuclein aggregation. A correlation between two changes measured after treatment does not order dysbiosis before enteric alpha-synuclein misfolding, which is the question this gap asks.

+ 1 more reference

Which Parkinson disease risk and causal variants produce convergent dopaminergic-neuron mechanisms in a controlled human genetic background, and which phenotypes are variant-specific, modifier-dependent, or culture artifacts?

KNOWLEDGE GAP OPEN gap_pd_variant_specific_isogenic_hpsc_mechanisms

Attached to

pathophysiology#Dopaminergic Neuron Loss pathophysiology#Alpha-Synuclein Aggregation pathophysiology#Mitochondrial Dysfunction pathophysiology#Autophagy-Lysosome Pathway Dysfunction

Patient-derived iPSC comparisons are powerful but confounded by background genetic variation. Large WGS-QC'd isogenic hPSC panels, differentiated into midbrain dopaminergic neurons and phenotyped with imaging and sequencing, can separate variant-specific causal mechanisms from shared downstream neurodegenerative states.

Proposed experiments

Automated isogenic hPSC Parkinson variant panel

high-throughput isogenic stem-cell perturbation experiment

exp_pd_automated_isogenic_hpsc_variant_panel

Generate or extend a WGS-QC'd isogenic hPSC panel carrying high-risk or causal Parkinson disease alleles, differentiate lines into midbrain dopaminergic neurons, and benchmark variant-specific effects on alpha-synuclein handling, mitochondrial state, lysosomal function, and dopaminergic-neuron survival.

Model systems

Genome-edited hPSC-derived midbrain dopaminergic neuron panel

Isogenic human pluripotent stem cell collection carrying Parkinson disease variants, differentiated into disease-relevant dopaminergic neurons for mechanism-resolved phenotyping.

IPSC DERIVED MODEL PMID:38405931 link

human NCBITaxon:9606

midbrain dopaminergic neuron CL:0000700

Designed to be compatible with automated hPSC genome-engineering and clonal QC workflows such as ATTIS-style high-throughput line generation.

Perturbations

Parkinson disease variant editing

pathophysiology#Dopaminergic Neuron Loss

Introduce or compare causal and high-risk Parkinson alleles in a shared genetic background.

SNCA hgnc:11138 LRRK2 hgnc:18618 GBA1 hgnc:4177 PINK1 hgnc:14581 PRKN hgnc:8607

Prime-editing generation or correction

gene#LRRK2

Use prime editing or correction to create reciprocal disease and rescue alleles where feasible.

LRRK2 hgnc:18618

Readouts

Alpha-synuclein aggregation burden

pathophysiology#Alpha-Synuclein Aggregation

High-content imaging and biochemical readouts of alpha-synuclein accumulation in differentiated dopaminergic neurons.

high-content imaging immunocytochemistry

Direction: POSITIVE

Mitochondrial dysfunction

pathophysiology#Mitochondrial Dysfunction

Mitochondrial respiration, membrane-potential, and stress-state measurements across edited variants and corrected controls.

mitochondrial organization GO:0007005

mitochondrial respiration assay

Direction: NEGATIVE

Autophagy-lysosome pathway dysfunction

pathophysiology#Autophagy-Lysosome Pathway Dysfunction

Lysosomal function, autophagic flux, and transcriptomic readouts stratified by causal allele and rescue status.

autophagy GO:0006914

lysosomal function assay single-cell transcriptomic profiling

Direction: NEGATIVE

Dopaminergic neuron survival and identity

pathophysiology#Dopaminergic Neuron Loss

Cell survival, dopaminergic identity, and dopamine biosynthesis readouts after differentiation.

dopamine biosynthetic process GO:0042416

high-content imaging targeted transcriptomic profiling

Direction: NEGATIVE

Controls

Isogenic unedited parental hPSC line

Same genetic background without Parkinson-associated edits.

Corrected rescue alleles

Reciprocal correction of disease alleles where editing design allows.

Decision criterion

A mechanism is prioritized when multiple independently edited clones for the same variant show a reproducible phenotype that is attenuated by isogenic correction and maps to a declared pathophysiology node.

Would support

pathophysiology#Alpha-Synuclein Aggregation pathophysiology#Mitochondrial Dysfunction pathophysiology#Autophagy-Lysosome Pathway Dysfunction pathophysiology#Dopaminergic Neuron Loss

Would refute

pathophysiology#Alpha-Synuclein Aggregation pathophysiology#Mitochondrial Dysfunction pathophysiology#Autophagy-Lysosome Pathway Dysfunction

Show evidence (3 references)

PMID:38405931 SUPPORT In vitro / ex vivo

"we generated a collection of 65 human stem cell lines genetically engineered to harbor high risk or causal variants in genes associated with PD"

Demonstrates the feasibility of a large isogenic hPSC Parkinson variant collection for mechanism-resolved experiments.

PMID:38405931 SUPPORT In vitro / ex vivo

"rigorous quality controls, including whole-genome sequencing of each line."

Supports WGS-QC as a design requirement for the proposed panel.

+ 1 more reference

Show evidence (1 reference)

PMID:38405931 SUPPORT In vitro / ex vivo

"Our iSCORE-PD collection represents an easily accessible and valuable platform to study PD, which can be used by investigators to understand the molecular pathophysiology of PD in a human cellular setting."

Establishes the existence of a human isogenic hPSC resource for studying Parkinson molecular pathophysiology, while the specific knowledge gap remains the standardized phenotype-to-mechanism adjudication.

Weight loss is a long-observed non-motor symptom of Parkinson disease, yet its mechanisms remain incompletely understood. Which of the proposed pathways — metabolic dysregulation, neuroendocrine disruption, gastrointestinal dysfunction, cognitive decline, and pharmacologic effects — are primary drivers versus secondary consequences, and how do they interact across the disease course?

KNOWLEDGE GAP OPEN gap_pd_weight_loss_multifactorial_mechanisms

Attached to

pathophysiology#Dopaminergic Neuron Loss pathophysiology#Intestinal Inflammation and Barrier Dysfunction pathophysiology#Basal Ganglia Circuit Dysfunction

Weight loss exerts substantial morbidity and mortality in PD, yet limited mechanistic understanding constrains treatment options. The Gabriel et al. (2026) review identifies six interacting pathways: (1) metabolic dysregulation (altered energy expenditure or intake), (2) neuroendocrine disruption (leptin/ghrelin/GLP-1 signaling), (3) gastrointestinal dysfunction (dysmotility, malabsorption, barrier dysfunction), (4) cognitive decline (reduced appetite awareness), (5) dopaminergic-medication effects (appetite suppression), and (6) brain stimulation paradoxes (DBS-induced weight changes). The relative contribution and temporal ordering of these mechanisms remain unknown. Resolving cross-mechanism interactions would enable targeted metabolic interventions in PD.

Proposed experiments

Longitudinal weight loss phenotype stratification with multi-mechanism readouts

longitudinal multi-omics observational cohort study

exp_pd_weight_loss_longitudinal_mechanisms

Follow a large PD cohort with serial body composition (DXA, bioimpedance), resting metabolic rate, circulating metabolic hormones (leptin, adiponectin, GLP-1, ghrelin), dopamine-agonist doses and appetite-affecting medications, cognitive testing, gastrointestinal symptom questionnaires, and GI transit imaging. Stratify the cohort into weight-loss phenotypes (progressive vs. stable) and identify mechanistic signatures.

Readouts

Metabolic rate and body composition trajectories

pathophysiology#Dopaminergic Neuron Loss

Measure resting metabolic rate, energy expenditure, and changes in lean vs. fat mass to distinguish metabolic dysregulation from reduced intake.

indirect calorimetry dual-energy X-ray absorptiometry

Direction: NEGATIVE

Circulating neuroendocrine hormone patterns

pathophysiology#Dopaminergic Neuron Loss

Quantify leptin, ghrelin, adiponectin, GLP-1, and other appetite-regulating hormones to identify dysregulation of satiety/hunger signaling.

serum hormone quantification

Direction: NEGATIVE

Gastrointestinal function and symptoms

pathophysiology#Intestinal Inflammation and Barrier Dysfunction

Assess gastric emptying (breath test), small-bowel transit, colonic function, permeability markers (zonulin, calprotectin), and GI symptom severity to establish causal vs. consequential GI involvement.

gastric-emptying scintigraphy fecal calprotectin assay

Direction: NEGATIVE

Cognitive decline severity

pathophysiology#Basal Ganglia Circuit Dysfunction

Administer validated cognitive batteries (MoCA, MMSE) and assess appetite awareness to test the cognitive-suppression hypothesis.

cognitive assessment battery

Direction: NEGATIVE

Decision criterion

Mechanistic dominance is supported by: (1) trajectories preceding or independent of weight loss (dysmetabolism, hormone changes, GI dysfunction); (2) stratification of the cohort into mechanistically distinct weight-loss phenotypes; (3) reproducible associations between mechanism-specific markers and subsequent weight-loss progression in converters.

Would support

pathophysiology#Dopaminergic Neuron Loss pathophysiology#Intestinal Inflammation and Barrier Dysfunction pathophysiology#Basal Ganglia Circuit Dysfunction

Show evidence (2 references)

PMID:41781031 SUPPORT Other

"weight loss has long been observed in PD and other neurodegenerative disorders, yet the mechanisms remain incompletely understood. This limited mechanistic insight has left few treatment options for weight loss in PD."

The Gabriel et al. review establishes weight loss as a significant yet mechanistically unexplained PD symptom, directly motivating this knowledge gap.

PMID:41781031 SUPPORT Other

"Emerging research highlights the role of metabolic regulation, neuroendocrine signaling, pharmacologic treatment, cognitive decline, gastrointestinal dysfunction, and brain stimulation in shaping weight trajectories in PD."

This enumerates the six candidate mechanisms for weight loss in PD, supporting the multi-pathway framing of the gap.

Can brain-first versus body-first origin site be operationalized as a measurable layer of the biological staging frameworks for Parkinson disease, and does origin-site stratification carry mechanistic or prognostic information that the existing anchors and data-driven subtypes do not already capture?

KNOWLEDGE GAP OPEN gap_pd_origin_site_operationalization

Attached to

mechanistic_hypotheses#body_first_enteric_alpha_synuclein_model mechanistic_hypotheses#brain_first_central_alpha_synuclein_model

Both origin-site hypotheses in this entry are curated as ALTERNATIVE, and both are assigned in practice from proxies - premotor REM-sleep behavior disorder, autonomic markers, imaging asymmetry - rather than from an observed first site of alpha-synuclein pathology. Two current biological definitions of the disease, the neuronal alpha-synuclein disease integrated staging system and SynNeurGe, are built on alpha-synuclein seeding, neurodegeneration, genetics, and functional impairment; neither carries an origin-site axis. That is an implementation gap rather than evidence against either model, and it should not be read as a scientific qualification of the mechanism. But it leaves the practical question unanswered: no consensus operational definition of origin site exists, so origin-site subtype membership is not portable between cohorts, and there is no agreed way to record it alongside a biological stage. The prognostic side of the question is not favorable either - a 10-year PPMI comparison found that data-driven subtypes separate rapid progressors more efficiently than the pathological brain-first/body-first labels do. That comparison measures prognostic enrichment, not anatomical origin, so it does not test either mechanism; it does mean the case for adding an origin-site layer has to rest on mechanistic rather than prognostic grounds.

Recorded from the 2026 OpenScientist hypothesis-search reports for both origin-site models, which independently raise the missing origin-site layer as a curation-level knowledge gap. The two staging-framework citations and the progression-milestone comparison ground claims that the mechanistic_hypotheses notes previously asserted without references. An earlier preprint of the milestone comparison (PMID:40678221) reported lower milestone proportions (50%, 43%, 42%) than the final publication cited here; cite the published version.

Show evidence (3 references)

PMID:38267190 SUPPORT Other

"Our biological definition establishes a staging system, the neuronal α-synuclein disease integrated staging system (NSD-ISS), rooted in the biological anchors (S and D) and the degree of functional impairment caused by clinical signs or symptoms."

Names the anchors of the NSD-ISS - alpha-synuclein seeding, dopaminergic dysfunction, and functional impairment - none of which encodes where pathology began, which is the gap this discussion records.

PMID:39973492 SUPPORT Other

"However, SynNeurGe provides a broader, more flexible framework that integrates α-synuclein pathology (S), neurodegeneration (N), and genetics (G), linked to clinical features (C)."

The competing biological classification is organized on the same kind of axes, so the absence of an origin-site layer is common to both frameworks rather than particular to one.

PMID:42286020 SUPPORT Human clinical

"Data-driven subtypes exhibited the highest progression rates, with DM patients attaining 63.0% of milestones, surpassing PIGD (55.6%) and body-first (54.0%) subtypes."

Quantifies the prognostic half of the gap in the PPMI cohort: the body-first label is outperformed by a data-driven subtype for identifying rapid progressors. This bears on the utility of origin-site stratification for trial design, not on whether central or peripheral initiation occurs.

Does nigrostriatal dopaminergic degeneration produce a functionally leaky intestinal barrier in human Parkinson disease, given that two independent 6-hydroxydopamine rat studies report reduced zona occludens-1 with raised circulating lipopolysaccharide, while human colonic biopsies show disorganized tight junction morphology and yet no measurable change in para- or transcellular permeability?

HUMAN MODEL MISMATCH OPEN pd_brain_to_gut_tight_junction_translation

Attached to

pathophysiology#Intestinal Tight Junction Protein Loss pathophysiology#Striatal Dopamine Deficiency pathophysiology#Intestinal Inflammation and Barrier Dysfunction

The model evidence for a brain-to-gut arm is consistent and comes from two laboratories: lesioning the nigrostriatal dopaminergic system in rats lowers zona occludens-1 in colon and ileum, raises circulating lipopolysaccharide and intestinal fatty acid-binding protein, and shifts the microbiome. The human comparison has to be read carefully, because the two literatures do not measure the same thing. In colonic biopsies from 31 people with Parkinson disease, the protein reported as unchanged is zona occludens-1 by immunoblot on whole-biopsy lysate, whereas the reduced protein, occludin, was also assayed that way. By immunofluorescence, which is the modality both rodent studies used, the same cohort is clearly abnormal: a normal reticular pattern of occludin and zona occludens-1 staining was present in 6 of 8 controls but only 9 of 31 patients, and frankly disrupted morphology in 1 of 8 controls against 14 of 31 patients. So on the matched modality, human and rat agree that the junction is abnormal, and the apparent zona occludens-1 contradiction is at least partly a question of whether total abundance or spatial organization is being measured. What does not dissolve this way, and is the real content of this mismatch, is the functional result. Neither paracellular nor transcellular permeability differed from controls, while the rodent readouts predict a measurable leak. Three explanations are not distinguished by the present data. The measurements may simply be non-equivalent, since a junction can be visibly disorganized without losing enough barrier function to register as flux across a biopsy in an Ussing chamber. The rodent lesion is acute and unilateral where human nigrostriatal loss is gradual and partial, so the rat may model a rate rather than a state. Or the human intestine compensates, restoring function around an altered junctional architecture. One explanation can be set aside: this is not a levodopa artifact, because the authors found moderate to severe junctional disorganization in the five patients who had never received levodopa and no correlation between cumulative dose and the severity of altered permeability. Recording this as a HUMAN_MODEL_MISMATCH rather than a KNOWLEDGE_GAP is deliberate. The evidence is not absent on either side; it exists in both, and it is the translational validity of the rodent functional readout that is open. Note also what this mismatch does not touch. The brain-to-gut direction is a claim about a consequence of established dopaminergic loss and is independent of the brain-first versus body-first debate over where alpha-synuclein pathology begins, which is why the new edges carry no hypothesis group. The 6-hydroxydopamine model produces no alpha-synuclein pathology in the brain at all, so it cannot speak to that question.

Proposed experiments

Stage-stratified colonic tight junction panel in Parkinson disease

stage-stratified observational biopsy study

exp_pd_junctional_panel_by_disease_stage

Measure the junctional panel three ways in the same colonic biopsies, by immunoblot for total abundance, by immunofluorescence for spatial organization, and by flux for paracellular permeability, stratified by disease duration and including de novo patients and a prodromal group defined by REM sleep behavior disorder. Assaying all three on one specimen is the point, since the existing human study measured zona occludens-1 abundance and occludin abundance by immunoblot and organization by immunofluorescence, leaving the modality and the protein confounded.

Decision criterion

If organization is disrupted while abundance and flux are normal at every stage, the discordance is a measurement-equivalence result and the rodent abundance readout simply does not correspond to the human one. If flux rises in early or prodromal disease and normalizes later, the negative finding in established disease is a sampling-time artifact and the rodent model translates to a window. If flux is normal at every stage despite disrupted organization, human compensation is the surviving explanation.

Graded nigrostriatal lesion versus gut barrier response

dose-response perturbation study

exp_pd_dopaminergic_lesion_gradient_gut_barrier

Titrate nigrostriatal dopaminergic loss across a graded range in a rodent model, from partial loss comparable to early human disease up to the lesion extent used in existing 6-hydroxydopamine studies, reading out the full junctional protein panel and functional permeability at each level.

Decision criterion

If junctional and permeability change appear only above a lesion threshold steeper than human disease reaches, the human negative result is explained by lesion severity rather than by species. A barrier response at partial lesion levels would leave the species difference as the remaining explanation.

Raised from dismech issue #12152 ([kgap-scan] Parkinson's Disease: dopaminergic neurodegeneration and gut barrier dysfunction mechanism), which asked whether pathophysiology nodes should be added for dopamine-dependent regulation of gut barrier integrity. They were, as Intestinal Tight Junction Protein Loss plus two edges out of Striatal Dopamine Deficiency. This discussion records the human evidence that does not line up with them.

Show evidence (6 references)

PMID:25775153 REFUTE Human clinical

"By contrast to occludin, no change in ZO-1 expression levels was observed in PD"

Refutes the specific rodent claim that zona occludens-1 abundance falls in Parkinson disease colon. The measurement is an immunoblot on whole-biopsy lysate, which is the modality qualification this discussion turns on.

PMID:25775153 SUPPORT Human clinical

"TJs morphology was disrupted and irregularly distributed in the mucosa of 1 out of 8 controls"

The other half of the same paper, split into its own item because it cuts the opposite way. By immunostaining, the modality the rodent studies used, junctional morphology is disrupted in 14 of 31 patients against 1 of 8 controls, so the human junction is abnormal after all.

PMID:25775153 REFUTE Human clinical

"The para- and transcellular permeability were not different between PD patients and controls."

The functional counterpart of the same mismatch. The rodent model predicts a measurable leak, and this cohort did not show one by either route.

+ 3 more references

⚙

Pathophysiology

Dopaminergic Neuron Loss

Progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta is the core neuropathological lesion of Parkinson's disease. Motor signs emerge once an estimated 60-80% of these neurons are lost and the resulting loss of nigrostriatal dopamine input can no longer be compensated.

Dopaminergic Neuron CL:0000700

Dopamine Biosynthesis GO:0042416

substantia nigra UBERON:0002038

Experimental models

Midbrain organoids with dopaminergic differentiation ORGANOID Organoids contain dopaminergic neurons, but the progressive, age-dependent course of their loss in patients is rarely reproduced.

Animal models

Drosophila Dap160 heterozygous null with human alpha-synuclein expression Drosophila melanogaster perturbs Reduced Dap160 dosage enhances the neurodegeneration and motor decline caused by overexpressed human alpha-synuclein.

Downstream

Striatal Dopamine Deficiency Degeneration of substantia nigra pars compacta neurons removes the nigrostriatal projection, depleting dopamine in the striatum.

Show evidence (1 reference)

PMID:37048085 SUPPORT

"Tremor, shaking, movement problems, and difficulty with balance and coordination are among the hallmarks, and dopaminergic neuronal loss in substantia nigra pars compacta of the brain and aggregation of intracellular protein α-synuclein are the pathological characterizations."

This review confirms that dopaminergic neuronal loss in the substantia nigra pars compacta is a pathological hallmark of Parkinson's disease, supporting the core mechanism of dopaminergic neuron degeneration.

Striatal Dopamine Deficiency

Degeneration of nigrostriatal dopaminergic terminals depletes dopamine in the striatum, the principal input nucleus of the basal ganglia. Reduced striatal dopamine withdraws normal modulation of medium spiny projection neurons and is the proximate biochemical deficit linking nigral neuron loss to the motor features of Parkinson's disease.

Striatal medium spiny neuron CL:1001474

Dopaminergic synaptic transmission GO:0001963 ↓ DECREASED Dopamine Secretion GO:0014046 ↓ DECREASED

striatum UBERON:0002435

Computational models

Whole Dopaminergic Neuron SBML Model KINETIC Models dopamine synthesis, storage, release, reuptake, and degradation in dopaminergic-neuron physiology.

PD Map Cohort-Specific Probabilistic Boolean Models BOOLEAN NETWORK CaSQ, pyMaBoSS, CellDesigner Dopamine transcription pathways are among the enriched PD map diagrams converted to Boolean models and show distinct behaviour across subtypes.

Downstream

Basal Ganglia Circuit Dysfunction Loss of striatal dopamine unbalances the direct and indirect basal ganglia pathways.

Intestinal Tight Junction Protein Loss Selective nigrostriatal dopaminergic lesioning is followed by loss of intestinal tight junction protein, establishing a brain-to-gut direction alongside the gut-to-brain chain curated elsewhere in this entry. Neither lesion study identifies the mediating route, whether autonomic, endocrine, or humoral, so the link is recorded with unknown intermediates.

Gut Microbiome Dysbiosis The same nigrostriatal lesion shifts gram-negative bacterial classes and lowers short-chain fatty acid levels, so PD-associated dysbiosis is in part a consequence of central dopaminergic loss rather than only a proposed upstream trigger of it. This edge closes a feedback loop with the body-first chain instead of replacing it.

Show evidence (1 reference)

PMID:28332488 SUPPORT

"Neuronal loss in the substantia nigra, which causes striatal dopamine deficiency, and intracellular inclusions containing aggregates of α-synuclein are the neuropathological hallmarks of Parkinson disease."

This review identifies striatal dopamine deficiency as a defining neuropathological hallmark of Parkinson's disease.

Basal Ganglia Circuit Dysfunction

Striatal dopamine loss shifts the basal ganglia-thalamocortical motor circuit toward excessive inhibitory output: the indirect pathway becomes hyperactive and the direct pathway hypoactive, increasing inhibitory drive from the globus pallidus pars interna onto the motor thalamus and cortex. This aberrant circuit activity, rather than neuron loss alone, generates the cardinal motor signs of Parkinson's disease.

Striatal medium spiny neuron CL:1001474 GABAergic neuron CL:0000617

GABAergic synaptic transmission GO:0051932 ↕ DYSREGULATED

basal ganglia UBERON:0002420

Computational models

Basal Ganglia Spiking Neural Network PHYSIOLOGICAL Models dopamine-modulated basal ganglia circuit dynamics, beta-band oscillations, and DBS effects.

Downstream

Resting Tremor

Bradykinesia

Rigidity

Postural Instability

Freezing of Gait Freezing is attributed to global motor-circuit dysfunction arising from the excitatory/inhibitory imbalance within the basal ganglia, and its responsiveness to the dopaminergic medication cycle marks a motor component. The intermediates are not resolved: the same source attributes freezing additionally to impaired cognitive, attentional and visuospatial networks outside this node.

Show evidence (2 references)

PMID:18781672 SUPPORT

"The parkinsonian state is characterized by disruption of the internal balance of the BG leading to hyperactivity in the two main entry points of the network (striatum and STN) and excessive inhibitory output from the GPi."

This review characterizes the parkinsonian basal ganglia by disrupted internal balance and excessive inhibitory GPi output, supporting basal ganglia circuit dysfunction as a distinct mechanism node.

PMID:30897356 SUPPORT

"We will then describe the basal ganglia-thalamocortical circuit, the major locus of PD-related circuit dysfunction, and some of the models that have influenced its study."

This review identifies the basal ganglia-thalamocortical circuit as the major locus of PD-related circuit dysfunction.

Alpha-Synuclein Aggregation

Misfolded alpha-synuclein protein accumulates to form Lewy bodies and Lewy neurites. These aggregates spread through the nervous system in a prion-like manner, contributing to neurodegeneration.

inclusion body assembly GO:0070841

Experimental models

Midbrain organoids with dopaminergic differentiation ORGANOID Alpha-synuclein accumulation is reproduced in SNCA triplication organoid models.

Animal models

Drosophila Dap160 heterozygous null with human alpha-synuclein expression Drosophila melanogaster measures Dap160 colocalizes with alpha-synuclein aggregates at synaptic boutons.

Computational models

Alpha-Synuclein Aggregation BST Model KINETIC Models alpha-synuclein aggregation kinetics and degradation-pathway effects in dopaminergic neurons.

Alpha-Synuclein Prion-like Spreading Model AGENT BASED Models connectome-based propagation of misfolded alpha-synuclein pathology.

Downstream

Dopaminergic Neuron Loss

Neuroinflammation

Nigral Cellular Senescence Alpha-synuclein pathology is one of the two recorded routes into the nigral senescence node. Injected preformed fibrils drive the senescence marker changes in mouse glia, and reduced SATB1 protein in human PD midbrain connects that pathology to the dopaminergic-neuron arm of the same node. What links fibril uptake to the arrest is not established.

Show evidence (3 references)

PMID:38245249 SUPPORT

"Parkinson's disease is a progressive neurodegenerative condition associated with the deposition of aggregated α-synuclein."

This authoritative Lancet review establishes that aggregated α-synuclein deposition is a defining feature of Parkinson's disease pathogenesis.

PMID:38245249 SUPPORT

"Biochemical studies, investigation of transplanted neurons in patients with Parkinson's disease, and cell and animal model studies suggest that abnormal aggregation of α-synuclein and spreading of pathology between the gut, brainstem, and higher brain regions probably underlie the development..."

This provides direct evidence for the prion-like spreading mechanism of α-synuclein pathology across neural networks, supporting the mechanism of trans-neuronal propagation.

PMID:36598534 SUPPORT

"Parkinson's disease (PD) is the second most common neurodegenerative disease, and is characterized by accumulation of α-synuclein (α-syn)."

Confirms that α-synuclein accumulation is a key pathological characterization of PD, reinforcing the central role of protein aggregation in disease pathology.

Mitochondrial Dysfunction

Impaired mitochondrial function, particularly complex I deficiency, leads to oxidative stress and neuronal death. Multiple PD genes (PINK1, Parkin, DJ-1) regulate mitochondrial quality control.

PINK1 hgnc:14581 PRKN hgnc:8607 FBXO7 hgnc:13586 VPS13C hgnc:23594 CHCHD2 hgnc:21645

mitochondrion organization GO:0007005 Oxidative phosphorylation (complex I deficiency) GO:0006119 ↓ DECREASED Mitophagy (PINK1/Parkin quality control) GO:0000422 ↓ DECREASED Reactive oxygen species metabolism (oxidative stress) GO:0072593 ↑ INCREASED

Experimental models

Midbrain organoids with dopaminergic differentiation ORGANOID Organoids reproduce mitochondrial dysfunction as reported in the reviewed organoid studies.

Computational models

Whole Dopaminergic Neuron SBML Model KINETIC Models mitochondrial metabolism alongside dopamine handling in dopaminergic neurons.

Downstream

Dopaminergic Neuron Loss

Show evidence (7 references)

PMID:38245249 SUPPORT

"At a cellular level, abnormal mitochondrial, lysosomal, and endosomal function can be identified in both monogenic and sporadic Parkinson's disease, suggesting multiple potential treatment approaches."

This establishes that mitochondrial dysfunction is a common cellular feature across both genetic and sporadic forms of PD, supporting its central role in disease pathogenesis.

PMID:25611507 SUPPORT

"Biochemical and genetic studies reveal that the products of two genes that are mutated in autosomal recessive parkinsonism, PINK1 and Parkin, normally work together in the same pathway to govern mitochondrial quality control, bolstering previous evidence that mitochondrial damage is involved in..."

This directly supports the role of PINK1 and Parkin genes in mitochondrial quality control and confirms that mitochondrial damage is involved in PD pathogenesis.

PMID:27911343 SUPPORT

"For the past 30 years, mitochondrial dysfunction has been hypothesized to play a central role in the pathobiology of this devastating neurodegenerative disease. The identifications of mutations in genes encoding PINK1 (PTEN-induced kinase 1) and Parkin (E3 ubiquitin ligase) in familial PD and..."

This review confirms the long-standing central role of mitochondrial dysfunction in PD and validates the connection between PINK1/Parkin mutations and mitochondrial quality control defects.

+ 4 more references

PGC-1alpha Transcriptional Program Repression

Mechanism confidence: Established

Reduced activity of the PPARGC1A-encoded transcriptional coactivator PGC-1alpha downregulates the nuclear-encoded bioenergetic program it drives - mitochondrial biogenesis, respiratory-chain subunit expression, and antioxidant defenses - in nigral dopaminergic neurons. Two routes converge on this node. In the parkin-dependent route, loss of parkin E3 ligase function allows its substrate PARIS (ZNF746) to accumulate and transcriptionally repress the PPARGC1A promoter. In sporadic disease, PGC-1alpha-responsive bioenergetic gene sets are already underexpressed in laser-captured human nigral dopaminergic neurons at subclinical stages, placing this lesion early in the cascade rather than as a terminal consequence of neuron loss. The therapeutic corollary is not symmetric: restoring PGC-1alpha rescues dopaminergic neurons in cellular models, but sustained supraphysiological expression is itself toxic to the nigrostriatal system (see the HUMAN_MODEL_MISMATCH discussion pd_pgc1a_therapeutic_window).

nigral dopaminergic neuron CL:0000700

mitochondrial biogenesis program GO:0007005 ↓ DECREASED

transcription coactivator activity GO:0003713 ↓ DECREASED

Downstream

Mitochondrial Dysfunction Loss of PGC-1alpha coactivation lowers expression of nuclear-encoded respiratory-chain subunits, producing the electron-transport deficit already curated on the Mitochondrial Dysfunction node.

Oxidative Stress PGC-1alpha coordinates the antioxidant arm of the mitochondrial stress response, so its repression lowers reactive-oxygen-species buffering capacity in nigral neurons.

Show evidence (3 references)

PMID:21376232 SUPPORT Human clinical

"PARIS is a KRAB and zinc finger protein that accumulates in models of parkin inactivation and in human PD brain."

Establishes that the repressor upstream of PGC-1alpha accumulates in human Parkinson disease brain, not only in experimental models.

PMID:21376232 SUPPORT Model organism

"Conditional knockout of parkin in adult animals leads to progressive loss of dopamine (DA) neurons in a PARIS-dependent manner."

Genetic epistasis in adult conditional parkin knockout mice shows the dopaminergic loss is routed through PARIS, the PPARGC1A repressor.

PMID:20926834 SUPPORT Human clinical

"Genes controlling cellular bioenergetics that are expressed in response to peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) are underexpressed in Parkinson's disease patients."

Direct human transcriptomic evidence that the PGC-1alpha-responsive program is underexpressed in Parkinson disease, which is the claim this node asserts.

MAPK Dysregulation

Dysregulation of mitogen-activated protein kinase (MAPK) signaling, particularly through overactivation of the JNK and p38 cascades, accelerates neurodegeneration and promotes alpha-synuclein accumulation and microglial activation. While basal MAPK activity is essential for neuroprotection and neuronal growth, pathological MAPK overactivation inhibits neuroprotective PI3K/AKT and PP2A pathways and activates detrimental GSK-3β and PTEN signaling, driving dopaminergic neurotoxicity.

Dopaminergic Neuron CL:0000700 Microglia CL:0000129

MAPK cascade GO:0000165 ↑ INCREASED JNK cascade GO:0007254 ↑ INCREASED p38MAPK cascade GO:0038066 ↑ INCREASED

Downstream

Alpha-Synuclein Aggregation MAPK dysregulation promotes alpha-synuclein accumulation.

Neuroinflammation MAPK overactivation drives microglial activation and pro-inflammatory cytokine release.

Dopaminergic Neuron Loss MAPK-driven oxidative stress, impaired neuroprotection, and neuroinflammation converge to promote dopaminergic neurotoxicity.

Show evidence (2 references)

PMID:42320726 SUPPORT Other

"While basal MAPK activity is essential for neuroprotection and neuronal growth, its overactivation, specifically via the JNK and p38 cascades, accelerates neurodegeneration."

This review establishes MAPK/JNK/p38 overactivation as a central driver of PD neurodegeneration, providing strong evidence for MAPK dysregulation as a distinct pathophysiological node.

PMID:42320726 SUPPORT Other

"highlights critical crosstalk between MAPK and other vital pathways, including the inhibition of the neuroprotective PI3K/AKT and PP2A pathways and the detrimental activation of GSK-3β and PTEN signaling."

This describes the broader signaling context of MAPK dysregulation, including inhibition of neuroprotective and activation of pro-degenerative pathways.

Neuroinflammation

Sustained glial activation in the PD brain, driven principally by microglia, with pro-inflammatory cytokine release (TNF-α, IL-1β, IL-6), M1-like phenotype polarization, and complement cascade activation. Reactive astrocytes feed this state through their own release of inflammatory mediators; that arm is modeled separately as Reactive Astrogliosis.

Microglia CL:0000129 Astrocyte CL:0000127

Microglial activation GO:0001774 ↑ INCREASED TNF-alpha production GO:0032640 ↑ INCREASED IL-1beta production GO:0032611 ↑ INCREASED IL-6 production GO:0032635 ↑ INCREASED

Downstream

Dopaminergic Neuron Loss

Complement C3-C3aR Activation in Depression Microglial neuroinflammation drives complement cascade activation (C3-C3aR axis) as part of the broader innate immune response, with convergent upregulation of complement and coagulation pathways in depression associated with PD. This complement-mediated branch contributes to depression-like behavior via microglial synaptic pruning, distinct from dopaminergic motor pathology.

Show evidence (7 references)

PMID:38245249 SUPPORT

"Recent work has also highlighted maladaptive immune and inflammatory responses, possibly triggered in the gut, that accelerate the pathogenesis of Parkinson's disease."

This establishes that maladaptive immune and inflammatory responses play an active role in accelerating PD pathogenesis, supporting the neuroinflammation mechanism.

PMID:37048085 SUPPORT

"Neuroinflammation has emerged as an involving mechanism at the initiation and development of PD. It is a complex network of interactions comprising immune and non-immune cells in addition to mediators of the immune response. Microglia, the resident macrophages in the CNS, take on the leading..."

This directly supports the role of microglia-mediated neuroinflammation in PD initiation and progression, confirming the importance of microglial activation in disease pathology.

PMID:36598534 SUPPORT

"Neuroinflammation driven by microglia is an important pathological manifestation of PD. α-Syn is a crucial marker of PD, and its accumulation leads to microglia M1-like phenotype polarization, activation of NLRP3 inflammasomes, and impaired autophagy and phagocytosis in microglia."

This links α-synuclein accumulation to microglial activation and pro-inflammatory M1 phenotype polarization, supporting the mechanism by which neuroinflammation contributes to neurodegeneration in PD.

+ 4 more references

Reactive Astrogliosis

Conversion of astrocytes from a homeostatic, broadly neuroprotective state — neurotrophic factor secretion, blood-brain barrier regulation, and water-electrolyte and glutamate homeostasis — to a reactive state that releases inflammatory mediators, fails to clear synaptic glutamate, and triggers oxidative stress. Studies indicate that mutations in PD-associated genes may induce functional alterations in astrocytes; the cited review names no individual genes, so no per-gene claim is made here. Whether astrocytes protect or accelerate dopaminergic degeneration is regulated by bidirectional astrocyte-neuron and astrocyte-glia crosstalk.

Astrocyte CL:0000127

Astrocyte activation GO:0048143 ↑ INCREASED Astrocytic clearance of synaptic glutamate GO:0098712 ↓ DECREASED

Downstream

Dopaminergic Neuron Loss

Neuroinflammation Reactive astrocytes release inflammatory mediators, adding an astrocytic arm to the glial inflammatory state that microglia principally drive.

Oxidative Stress

Blood-Brain Barrier Dysfunction Astrocytes are one of the cell types regulating the blood-brain barrier, so loss of that homeostatic function on reactive conversion is a route into barrier breakdown. The cited review establishes the astrocytic BBB-regulatory role but does not itself report barrier breakdown caused by reactive astrocytes, so this edge is left uncited rather than over-claimed.

Show evidence (2 references)

PMID:42599550 SUPPORT Other

"Recent studies indicate that mutations in PD-associated genes may induce functional alterations in astrocytes."

Supports a genetic contribution to astrocyte dysfunction in PD, hedged as "may induce functional alterations" and naming no individual gene.

PMID:42599550 SUPPORT Other

"Furthermore, bidirectional regulatory interactions exist between astrocytes and both dopaminergic neurons and other glial cells in PD."

Identifies bidirectional astrocyte-neuron and astrocyte-glia crosstalk as the regulator of which arm predominates.

Complement C3-C3aR Activation in Depression

Elevated complement cascade activation, particularly the C3-C3aR signaling axis, drives microglial synaptic engulfment and loss. In depression associated with Parkinson disease, hippocampal complement components (C1Q, C3, C3aR) and downstream signaling (p-STAT3, p-P65) are upregulated, promoting microglial phagocytosis of synapses and contributing to depressive symptoms. This represents a distinct complement-mediated pathogenic pathway in depression, separable from canonical dopaminergic motor circuit involvement.

Microglia CL:0000129

complement activation GO:0006956 ↑ INCREASED synapse pruning GO:0098883 ↑ INCREASED

hippocampal formation UBERON:0002421

Downstream

Depression Complement C3-C3aR-mediated microglial synaptic engulfment leads to hippocampal synaptic loss and dysfunction, manifesting as depression and mood disturbance in Parkinson disease.

Show evidence (3 references)

PMID:42263400 SUPPORT Model organism

"In MPTP-treated male and female mice, hippocampal complement components (C1Q, C3, C3aR) and downstream signalling (p-STAT3, p-P65) were elevated, accompanied by microglial synapse phagocytosis and depressive-like behaviours."

MPTP mouse model demonstrates upregulation of complement cascade components in hippocampus alongside microglial synaptic phagocytosis and depression-like behaviors, establishing the complement pathway as a mechanism driving depression in PD.

PMID:42263400 SUPPORT Human clinical

"DPD exhibits distinct sex-specific immune signatures, with convergent complement pathway activation driving microglial synaptic pruning and depressive symptoms."

Human plasma proteomic analysis from PPMI cohort reveals that depression in PD exhibits sex-specific complement pathway dysregulation, establishing complement activation as a mechanism contributing to depressive symptoms.

PMID:42263400 SUPPORT Model organism

"The antidepressant effect of BoNT/A is mediated through inhibition of the C3-C3aR signalling axis."

Mouse model studies demonstrate that complement pathway inhibition (via BoNT/A blocking C3-C3aR signaling) alleviates depressive-like symptoms and reduces microglial synaptic engulfment, providing mechanistic validation of C3-C3aR as a therapeutic target in depression.

Serotonergic Raphe Neuron Loss

Degeneration of serotonergic neurons in the raphe nuclei removes serotonergic modulation of limbic circuitry. This is a non-dopaminergic arm of the neurodegeneration and is the mechanism the reviewed literature attributes the neuropsychiatric non-motor symptoms to, distinguishing them from the motor signs produced by nigrostriatal dopamine loss.

serotonergic neuron CL:0000850

raphe nuclei UBERON:0004684

Downstream

Anxiety Loss of serotonergic modulation of limbic and fear circuitry is the route by which PD neuropathology is reported to promote anxiety. The intermediates within those circuits are not resolved in the cited source.

Apathy Loss of serotonergic modulation is one of the two transmitter deficits the reviewed literature attributes apathy to. The source names dopamine alongside serotonin and states the relation as a belief rather than a demonstrated mechanism, so this edge carries the serotonergic arm only and resolves no intermediates.

Show evidence (1 reference)

PMID:42646502 SUPPORT REVIEW SYNTHESIS Other

"Serotonin ↓ | Impairment and loss of serotonergic neurons within the raphe nuclei, which are responsible for modulating the limbic circuits and circadian rhythms. | Neuropsychiatric and vegetative symptoms: Depression, anxiety, sleep fragmentation, and sleep disturbances."

Establishes the node itself: raphe serotonergic neuron loss as a distinct non-dopaminergic mechanism in PD.

Posterior Cortical and Limbic Atrophy

Atrophy of posterior visual-association cortex together with limbic and thalamic structures accompanies the psychosis syndrome of Parkinson disease. It is the anatomical correlate the reviewed literature links hallucinations to, and is distinct from the nigrostriatal degeneration driving motor signs.

precuneus UBERON:0006093 occipital lobe UBERON:0002021 hippocampus UBERON:0002421

Downstream

Hallucinations Hallucinations in PD psychosis are reported as linked to atrophy of visual-association, limbic and thalamic regions. The source states an anatomical association rather than a demonstrated causal sequence, and names no intermediate steps.

Show evidence (2 references)

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"Hallucinations in PD are linked to cortical atrophy in areas like the cuneus, precuneus, occipital gyrus, lingual and fusiform gyri, supramarginal and angular gyri, anterior cingulate, hippocampus, and thalamus."

Names atrophy in the posterior-cortical and limbic regions this node records and that its locations bind, which is the node's central assertion.

PMID:42646502 SUPPORT REVIEW SYNTHESIS Other

"Abnormal brain connections lead to false perceptions."

The review's framing sentence for PD psychosis. It asserts a connectivity basis for false perceptions and names no anatomy, so it supports the node only as general context.

Autophagy-Lysosome Pathway Dysfunction

Impairment of the autophagy-lysosome pathway disrupts clearance of misfolded proteins including alpha-synuclein. Multiple PD genes (GBA, LRRK2, VPS35, ATP13A2) regulate lysosomal function, and their mutations impair protein degradation capacity leading to toxic protein accumulation.

Dopaminergic Neuron CL:0000700

GBA1 hgnc:4177 LRRK2 hgnc:18618 SNCA hgnc:11138 PRKN hgnc:8607 PINK1 hgnc:14581 VPS35 hgnc:13487

Autophagy GO:0006914 Chaperone-mediated Autophagy GO:0061684

Experimental models

Midbrain organoids with dopaminergic differentiation ORGANOID Organoids reproduce lysosomal dysfunction as reported in the reviewed organoid studies.

Computational models

PD Map Cohort-Specific Probabilistic Boolean Models BOOLEAN NETWORK CaSQ, pyMaBoSS, CellDesigner PRKN mitophagy is one of the enriched PD map pathways converted into a cohort-parameterised Boolean model, and autophagy/mitophagy activity is one of the axes on which the subtypes separate.

Downstream

Alpha-Synuclein Aggregation

Dopaminergic Neuron Loss

Show evidence (5 references)

PMID:31761667 SUPPORT

"In recent years, multiple lines of evidence from human genetic and molecular studies have highlighted the importance of the autophagy lysosomal pathway (ALP) in Parkinson's disease (PD). Genes such as GBA and LRRK2, which harbor some of the most common mutations associated with PD, have..."

This review establishes the genetic basis for autophagy-lysosome dysfunction in PD, identifying key genes and their mechanistic roles.

PMID:31761667 SUPPORT Human clinical

"Numerous other PD-related genes, such as PRKN, PINK1, TMEM175, SMPD1, CTSD, CTSB and many more, have also been reported to have important roles in the ALP."

Supports binding PRKN and PINK1 to this node in addition to the mitochondrial node, since the same review places both in the autophagy-lysosome pathway.

PMID:31761667 SUPPORT Human clinical

"mutations/multiplications in SNCA may lead to impairment of chaperone mediated autophagy or other ALP functions"

Supports binding SNCA to this node, since SNCA variation is reported to impair chaperone-mediated autophagy, one of the two processes bound on the node.

+ 2 more references

LRRK2 GTPase Domain Dysregulation

Leucine-rich repeat kinase 2 (LRRK2) mutations disrupt the conformational dynamics of its ROC (Ras of complex proteins) G-domain, impairing GTPase activity and nucleotide (GTP/GDP) cycling. The arginine residue at position 1398 acts as a critical GTP-γ-phosphate sensor that regulates the ROC domain's active-to-inactive state transition. Pathogenic ROC/GTPase-domain mutations (e.g., R1441C/G/H) impair GTP hydrolysis, stabilize the constitutively active GTP-bound state, and enhance Rab29-dependent recruitment of LRRK2 to the trans-Golgi network. This dysregulation impairs vesicular trafficking, autophagosome-lysosome fusion, and clearance of alpha-synuclein aggregates, promoting neurodegeneration. Protective variants (e.g., R1398H) stabilize the GDP-bound inactive state and reduce disease risk, suggesting that GTPase domain normalization rather than kinase inhibition may be a disease-modifying therapeutic strategy.

Dopaminergic neuron CL:0000700 Neuron CL:0000540

LRRK2 hgnc:18618

Autophagy GO:0006914 ↓ DECREASED Intracellular protein localization GO:0008104 ↕ DYSREGULATED Vesicle-mediated transport GO:0016192 ↓ DECREASED

Downstream

Autophagy-Lysosome Pathway Dysfunction Dysregulated LRRK2 GTPase activity impairs Rab29-dependent autophagosome-lysosome fusion and alpha-synuclein clearance.

Dopaminergic Neuron Loss Impaired protein clearance and autophagy promote accumulation of toxic protein aggregates and neuronal death.

Show evidence (3 references)

PPR:PPR1263597 Preprint · not peer-reviewed SUPPORT In vitro / ex vivo

"A naturally occurring protective variant, R1398H, provides an alternative route for understanding how reduced disease risk may be achieved by tuning the regulatory GTPase domain rather than the kinase domain itself."

Preprint demonstrates that GTPase domain tuning via protective R1398H variant may be a disease-modifying strategy, supporting the model that ROC domain conformational control is critical for LRRK2-related PD.

PPR:PPR1263597 Preprint · not peer-reviewed SUPPORT In vitro / ex vivo

"Purified ROC carrying R1398H is folded but resolves as a stable homodimer corresponding to the GDP-bound off state previously defined for wild-type ROC."

Biochemical analysis demonstrates that the protective R1398H variant stabilizes the inactive GDP-bound state, providing structural evidence for GTPase domain regulation as a disease-modifying mechanism.

PPR:PPR1263597 Preprint · not peer-reviewed SUPPORT In vitro / ex vivo

"R1398H reduces GTP hydrolysis, selectively weakens GTP-state stabilization while preserving GDP binding, and decreases Rab29-dependent trans-Golgi recruitment of full-length LRRK2."

The protective variant reduces aberrant trans-Golgi recruitment, supporting the model that GTPase domain normalization may prevent pathological LRRK2 localization and consequent autophagy impairment.

Gut Microbiome Dysbiosis

Parkinson disease cohorts show reproducible but modest gut microbiome shifts, including depletion of short-chain-fatty-acid-producing taxa and enrichment of genera linked to mucin or inflammatory biology. In the body-first model, dysbiosis is modeled as a plausible upstream trigger or modifier of intestinal inflammation and barrier dysfunction, not as an established direct cause of alpha-synuclein initiation.

Body-First Enteric α-Synuclein Initiation Model

Enteroendocrine Cell CL:0000164

intestine UBERON:0000160

Downstream

Intestinal Inflammation and Barrier Dysfunction PD-associated dysbiosis may promote a pro-inflammatory intestinal state and barrier dysfunction, but the direction and necessity of this link remain unresolved in humans.

Show evidence (2 references)

PMID:33692356 SUPPORT Human clinical

"We found significant alterations in the PD-associated microbiome, which are robust to study-specific technical heterogeneities, although differences in microbiome structure between PD and controls are small."

Meta-analysis across ten 16S datasets supports a reproducible PD-associated gut microbiome signature, while noting small effect sizes.

PMID:36332796 SUPPORT Other

"Alterations in the gut microbiome and associated metabolites may contribute to pathogenesis in PD."

Review-level evidence supports gut microbiome changes as plausible contributors to PD pathogenesis, but not as proven initiators.

Intestinal Tight Junction Protein Loss

Selective nigrostriatal dopaminergic injury depletes tight junction protein in the intestinal epithelium. In the 6-hydroxydopamine rat lesion model, zona occludens-1 falls in both ileum and colon and more markedly in the colon, while the enterocyte brush border is spared, making this a junctional lesion rather than generalized epithelial damage. The junctional loss is accompanied by rising circulating lipopolysaccharide and intestinal fatty acid-binding protein, the expected consequence of a leakier paracellular route. This node is where a brain-to-gut arm joins the body-first enteric chain curated elsewhere in this entry rather than running beside it. Its downstream target is the same barrier node the dysbiosis chain feeds, so the two directions converge and close a loop. Its human counterpart is only partly settled. Colonic biopsies from people with Parkinson disease show reduced occludin and disorganized staining of both junctional proteins, which agrees with the model, but no fall in zona occludens-1 by immunoblot and no measurable permeability change, which does not. That divergence is recorded as a HUMAN_MODEL_MISMATCH discussion rather than smoothed over here.

intestinal epithelial cell CL:0002563

tight junction organization GO:0120193 ↓ DECREASED

bicellular tight junction GO:0005923

colon UBERON:0001155 ileum UBERON:0002116

Downstream

Intestinal Inflammation and Barrier Dysfunction Depletion of tight junction protein raises paracellular permeability and permits translocation of luminal microbial product, measurable as rising circulating lipopolysaccharide and intestinal fatty acid-binding protein. The step to the barrier half of the target node is direct; the step to its inflammatory half runs through that translocation and the immune activation it provokes, which is why the link is recorded with known intermediates rather than as direct.

Show evidence (3 references)

PMID:42732868 SUPPORT Model organism

"the tight junction protein zona occludens-1 (ZO-1) had marked reductions in both the ileum and more profoundly in the colon, indicating regional vulnerability"

Establishes the node itself and its regional gradient, with the colon more affected than the ileum.

PMID:42732868 SUPPORT Model organism

"Immunostaining for Villin, an actin-binding protein in microvilli, revealed no changes to the enterocyte brush border in either the ileum or colon."

A negative result that narrows the node. The brush border is intact, so the lesion is specific to the junctional compartment rather than reflecting broad enterocyte injury.

PMID:37271045 SUPPORT Model organism

"6-OHDA decreased the Zonula occludens protein 1 barrier integrity score, suggesting increased colonic permeability."

Independent replication of the same junctional protein deficit after nigrostriatal lesioning, reported by a different group in a separate study.

Intestinal Inflammation and Barrier Dysfunction

Sporadic Parkinson disease is associated with elevated intestinal inflammatory and permeability markers. These changes may create a local milieu that increases alpha-synuclein expression or exposes enteric neurons to amyloidogenic microbial or dietary compounds, but whether they initiate body-first PD or arise secondary to gut autonomic dysfunction remains open.

Body-First Enteric α-Synuclein Initiation Model

Inflammatory Response GO:0006954

Downstream

Enteric Alpha-Synuclein Seeding Local gut inflammation and barrier leakiness may increase enteric alpha-synuclein expression or amyloidogenic exposure, providing a permissive setting for enteric alpha-synuclein seeding.

Show evidence (2 references)

PMID:34220443 SUPPORT Human clinical

"Calprotectin and zonulin are markers of intestinal inflammation and barrier permeability, respectively."

Establishes the measured marker interpretation for this intestinal inflammation and barrier dysfunction node.

PMID:34220443 SUPPORT Human clinical

"Mean calprotectin was higher in PD, both in serum (14.26 mcg/ml ± 4.50 vs. 5.94 mcg/ml ± 3.80, p = 0.0125) and stool (164.54 mcg/g ± 54.19 vs. 56.19 mcg/g ± 35.88, p = 0.0048)."

Case-control data support elevated intestinal inflammatory markers in PD.

Enteric Alpha-Synuclein Seeding

In the body-first model, misfolded alpha-synuclein appears first in enteric or peripheral autonomic neural tissue and serves as the initiating seed for subsequent gut-to-brain spread. Direct causal support comes primarily from animal models that seed pathologic alpha-synuclein in the gastrointestinal wall.

Body-First Enteric α-Synuclein Initiation Model

Enteric Neuron CL:0007011

inclusion body assembly GO:0070841

enteric nervous system UBERON:0002005

Downstream

Vagal-Brainstem Alpha-Synuclein Propagation Enteric alpha-synuclein seeds can propagate first to vagal brainstem nuclei and then to additional brain regions.

Constipation Enteric or autonomic involvement is a plausible contributor to early constipation in body-first PD, but this edge remains clinically inferred.

Show evidence (2 references)

PMID:31255487 SUPPORT Model organism

"fibrils were injected into the duodenal and pyloric muscularis layer"

The gut-to-brain transmission model experimentally seeds pathologic alpha-synuclein in the gastrointestinal wall.

PMID:34220443 SUPPORT Human clinical

"The coexistence of an amyloidogenic gut microbiota with intestinal inflammation (leading to local overexpression of alpha-synuclein) and altered intestinal barrier permeability (exposing alpha-synuclein to the amyloidogenic xenobiotics) may play a key role in triggering the initial..."

Human review/discussion within the marker study supports enteric alpha-synuclein seeding as a plausible but not proven event in some sporadic PD cases.

Vagal-Brainstem Alpha-Synuclein Propagation

Pathologic alpha-synuclein seeded in the gastrointestinal wall can propagate through vagal connections to the dorsal motor nucleus, nucleus tractus solitarius, caudal hindbrain, and ultimately midbrain and forebrain regions. Vagotomy experiments provide the strongest causal evidence for this body-first conduit.

Body-First Enteric α-Synuclein Initiation Model

vagus nerve UBERON:0001759 midbrain UBERON:0001891

Downstream

Alpha-Synuclein Aggregation Vagal-brainstem propagation links gut-origin pathology to the broader central alpha-synuclein aggregation cascade.

Pontine Tegmental Alpha-Synuclein Pathology As vagal-brainstem propagation continues rostrally, the pontine tegmentum - the site of the REM-atonia-generating circuit - is reached ahead of the nigrostriatal and cortical structures that define overt motor and cognitive disease.

Show evidence (2 references)

PMID:31255487 SUPPORT Model organism

"Analysis of human pathology led Braak to postulate that α-synuclein (α-syn) pathology could spread from the gut to brain via the vagus nerve."

Establishes the gut-to-brain vagal propagation hypothesis tested by the mouse transmission model.

PMID:39241780 SUPPORT Model organism

"α-Syn and Tau co-pathology can propagate from the gut to the brain, triggering behavioral disorders."

Supports gut-to-brain propagation in a gut-inducible transgenic mouse system.

Pontine Tegmental Alpha-Synuclein Pathology

Braak staging places pontine tegmental involvement ahead of substantia nigra pathology in the same caudo-rostral progression that vagal-brainstem propagation follows. The pontine tegmentum houses the glutamatergic REM-on circuit whose descending limb generates REM sleep muscle atonia. In Parkinson disease the lesion at this site is degenerative rather than structural, narcoleptic, or drug-induced, and it arrives at a topographic stage that precedes the nigrostriatal degeneration defining overt motor disease.

Body-First Enteric α-Synuclein Initiation Model

glutamatergic REM-on neuron of the sublaterodorsal nucleus CL:0000540 ↓ DECREASED

inclusion body assembly GO:0070841

sublaterodorsal nucleus UBERON:8440035 pons UBERON:0000988 brainstem UBERON:0002298

Downstream

Loss of Descending Drive to Inhibitory Premotor Neurons Pathology involving the pontine REM-on glutamatergic population removes the excitatory drive its descending axons carry to medullary and spinal inhibitory premotor neurons.

Show evidence (3 references)

PMID:20187227 SUPPORT Human clinical

"The proportion of cases that fit the PD staging scheme was 67% for incidental LBs; 86% for PSP with LBs; 86% for pure LBD; and 84% for LBD with AD"

Dickson's own autopsy series, rather than its statement of what Braak proposed: the caudo-rostral ordering that places pontine tegmental involvement before substantia nigra pathology holds in 84-86% of Lewy body disease cases. This is what licenses placing this node upstream of the nigrostriatal nodes in the pathograph.

PMID:17412731 SUPPORT Other

"The hypothesized pathophysiology of RBD is presented in relation to the Braak staging system for Parkinson's disease, in which the topography and temporal sequence of synuclein pathology in the brain could explain the evolution of parkinsonism and/or dementia well after the onset of RBD."

Ties the Braak sequence specifically to RBD pathophysiology rather than to brainstem involvement in general, which is the step that licenses placing this node upstream of the atonia nodes and that the staging paper alone does not make. Graded OTHER rather than HUMAN_CLINICAL because the quoted sentence states a hypothesis this Brain review advances, not a patient observation it reports - matching the grade `rem_sleep_atonia_control_failure.yaml` gives the comparable "is proposed as" sentence from the same paper.

PMID:39577924 SUPPORT Human clinical

"In all participants, α-synuclein was found in the structures that regulate REM sleep atonia (eg, subcoeruleus nucleus, gigantocellular reticular nucleus, laterodorsal tegmentum, and amygdala)"

Places the pathology in the atonia-generating nuclei themselves, not merely somewhere in the pontine tegmentum. The pontine tegmentum is a large region and Braak stage 2 is classically locus coeruleus and caudal raphe, so without this the lesion claim would rest on the region-level ordering alone. Note the inferential step: this cohort is isolated RBD rather than diagnosed Parkinson disease, so it evidences the lesion topography rather than its presence in established PD.

Loss of Descending Drive to Inhibitory Premotor Neurons

REM atonia is actively imposed rather than passively permitted: the glutamatergic REM-on population excites glycinergic and GABAergic premotor neurons in the ventromedial medulla and spinal cord, which hyperpolarise skeletal motor neurons. Losing the descending drive therefore releases motor neurons from an inhibition that should be present. This descending pathway is separate from the ascending pathway that generates the EEG features of REM sleep, so it can be lost while REM sleep itself proceeds normally - which is what polysomnography shows in Parkinson disease.

Body-First Enteric α-Synuclein Initiation Model

glutamatergic synaptic transmission GO:0035249 ↓ DECREASED inhibitory regulation of skeletal motor neuron output GO:0006937 ↓ DECREASED

brainstem UBERON:0002298

Downstream

REM Sleep Muscle Atonia Loss Without descending excitation of the inhibitory premotor pool, skeletal motor neurons are not hyperpolarised during REM sleep and muscle tone persists.

Show evidence (2 references)

PMID:17884926 SUPPORT Model organism

"In the REM-on area are two populations of glutamatergic neurons, the first of which projects to the basal forebrain and regulates EEG components of REM sleep and the second of which projects to the ventromedial medulla and spinal cord and regulates atonia during REM sleep."

The two-population anatomy this node depends on: a descending atonia limb separable from the ascending EEG limb.

PMID:17884926 SUPPORT Model organism

"Our findings demonstrating independent pathways mediating atonia and the EEG components of REM provide a basis for their occasional dissociation in pathological states, e.g. REM sleep behaviour disorder."

States the dissociation explicitly and names RBD as its pathological instance, which is what permits atonia to fail here while REM sleep itself is preserved.

REM Sleep Muscle Atonia Loss

Excess tonic or phasic electromyographic activity during scored REM sleep, the measurable abnormality that underlies dream enactment in Parkinson disease. Polysomnography confirms REM sleep without atonia in the majority of PD patients studied - more often than the clinical behavioural history alone identifies - so the electrophysiological finding runs ahead of, and is more sensitive than, a clinical diagnosis of REM sleep behavior disorder.

REM sleep GO:0042747 ⚠ ABNORMAL skeletal muscle contraction during REM sleep GO:0003009 ↑ INCREASED

Downstream

REM Sleep Behavior Disorder Where atonia loss is accompanied by dream-enactment behaviour rather than remaining electrophysiologically silent, the released motor programmes generated during dreaming are enacted, producing the clinical phenotype.

Show evidence (4 references)

PMID:12196654 SUPPORT Human clinical

"Nineteen (58%) of 33 patients with PD but only 1 of 16 control subjects had REM sleep without atonia."

Direct polysomnographic quantification of REM sleep without atonia in a PD cohort versus controls - the measurement this node's conformance claim requires.

PMID:12196654 SUPPORT Human clinical

"One third of patients with PD met the diagnostic criteria of RBD based on PSG recordings."

Shows the polysomnographic finding is more prevalent than, and only partly overlaps with, a clinical RBD diagnosis - consistent with the module's requirement that the electrophysiological finding, not the behavioural history, is what satisfies conformance at this node.

PMID:21832215 SUPPORT Human clinical

"An unselected cohort of sleep-disturbed patients with PD (n=457) was investigated with video-supported polysomnography."

Establishes the measurement method and scale behind the frequency below: video-supported polysomnography in an unselected PD cohort, an order of magnitude larger than the 33-patient series the rest of this node rests on.

+ 1 more reference

Central Alpha-Synuclein Initiation

In the brain-first model, the initial alpha-synuclein pathology begins in central sites such as the olfactory bulb or amygdala, then spreads through connected brain regions and later to peripheral autonomic structures. This node captures the competing central-origin route without asserting that it applies to all Parkinson disease.

Brain-First Central α-Synuclein Initiation Model

Dopaminergic Neuron CL:0000700

inclusion body assembly GO:0070841

olfactory bulb UBERON:0002264 amygdala UBERON:0001876

Downstream

Alpha-Synuclein Aggregation Central initiation feeds into the broader alpha-synuclein aggregation and propagation cascade through connected brain networks.

Show evidence (6 references)

PMID:38519273 SUPPORT Human clinical

"Molecular imaging studies were generally in agreement with the model, whereas structural imaging studies, such as MRI volumetry, showed conflicting findings."

Review-level synthesis supports the brain-first/body-first model while noting that not all imaging modalities agree.

PMID:32830221 SUPPORT Human clinical

"the PDRBD- data were compatible with a brain-first trajectory, characterized by primary loss of putaminal FDOPA uptake followed by a secondary loss of cardiac MIBG signal and 11C-donepezil signal."

Primary PET, MIBG, MRI, and gut-transit imaging evidence supports the central-first route by identifying a de novo PD subgroup with primary putaminal dopaminergic dysfunction followed by peripheral autonomic loss.

PMID:40209563 SUPPORT Human clinical

"The degeneration of amygdala is distinctively pronounced in "brain-first" Parkinson's disease, supporting differential disease progression patterns between subtypes."

Diffusion microstructure MRI gives the amygdala half of this node a human in vivo correlate: amygdala free interstitial fluid is higher in the brain-first group, matching the amygdala as a candidate central initiation site.

+ 3 more references

Nigral Cellular Senescence

Cells bearing senescence markers accumulate in the substantia nigra in Parkinson disease, in astrocytes and in the dopaminergic neurons themselves. Post-mortem nigral tissue carries raised p21, reduced nuclear lamin B1 and HMGB1, and the secreted factors of a senescence-associated secretory phenotype, among them IL-6, IL-1alpha, IL-8 and MMP-3. In dopaminergic neurons the transcriptional regulator SATB1 represses p21, so reduced SATB1 activity is the proposed route into a p21-dependent arrest in these post-mitotic cells. In mouse models the herbicide paraquat and alpha-synuclein preformed fibrils each induce glial senescence, and depleting senescent cells protects against paraquat-induced loss of nigral dopaminergic neurons.

Astrocyte CL:0000127 Dopaminergic Neuron CL:0000700

cellular senescence GO:0090398 ↑ INCREASED

Downstream

Neuroinflammation Route from the senescent nigral population to the neuroinflammation node: the senescent cells in parkinsonian substantia nigra carry a secretory phenotype whose measured components are cytokines the neuroinflammation node already holds. Which secreted factor reaches which glial population is not resolved, and one candidate was tested and found insufficient on its own.

Dopaminergic Neuron Loss Senescent cells contribute to nigral dopaminergic loss rather than only marking it. The evidence is interventional but entirely from the paraquat mouse model, where genetically depleting senescent cells preserves the dopaminergic marker that the exposure otherwise reduces. No human or alpha-synuclein-driven equivalent of the depletion experiment is recorded here.

Show evidence (8 references)

PMID:29386135 SUPPORT DIRECT Human clinical

"Here, we demonstrate that senescent cell markers are preferentially present within astrocytes in PD brain tissues."

The human observation behind the astrocyte binding on this node: senescence markers in PD brain tissue sit preferentially in astrocytes.

PMID:29386135 SUPPORT DIRECT Human clinical

"Astrocytes (GFAP+ cells) were found to be lamin B1 deficient in PD SNpc tissues while no significant difference was detected in PD versus aged-matched control tissues in non-astrocytic (GFAP−) neighboring cells"

Locates the lamin B1 loss in nigral astrocytes specifically, with the neighbouring non-astrocytic cells as the internal comparison. This is why the node names astrocytes rather than nigral tissue as a whole.

PMID:34359864 SUPPORT DIRECT Human clinical

"Our WB analysis revealed that the levels of Lamin B1 (Figure 7A,B), HMGB1 (Figure 7A,C) and SATB1 (Figure 7A,D) were substantially reduced, whereas the p21 level was significantly increased (Figure 7A,F) in the midbrain of human PD postmortem tissues compared to age- and gender-matched controls."

Independent human measurement of the marker set in PD midbrain, in eight cases against eight matched controls. It supports the lamin B1, HMGB1 and p21 changes this node describes, and reports reduced SATB1 protein, which is the link to the SATB1 mechanism.

+ 5 more references

Oxidative Stress

Excessive reactive oxygen species from dopamine metabolism and mitochondrial dysfunction causes lipid peroxidation, protein carbonylation, and DNA damage. Dopamine auto-oxidation generates toxic quinones that preferentially damage substantia nigra neurons.

Dopaminergic Neuron CL:0000700

Response to Oxidative Stress GO:0006979 ROS Metabolic Process GO:0072593

Downstream

Mitochondrial Dysfunction

Dopaminergic Neuron Loss

Alpha-Synuclein Aggregation

Show evidence (1 reference)

PMID:37303175 SUPPORT

"Reactive oxygen species (ROS)-induced oxidative stress triggers the vicious cycle leading to the degeneration of dopaminergic neurons in the nigra pars compacta."

This review directly describes the mechanism by which oxidative stress drives dopaminergic neurodegeneration.

Calcium Dysregulation

Substantia nigra dopaminergic neurons rely on L-type calcium channels (CaV1.3) for autonomous pacemaking, making them uniquely vulnerable to calcium-mediated toxicity. Disrupted calcium homeostasis in mitochondria, ER, and lysosomes contributes to oxidative stress and cell death.

Dopaminergic Neuron CL:0000700

Calcium Ion Homeostasis GO:0055074 Calcium Ion Transport GO:0070588

Downstream

Mitochondrial Dysfunction

Oxidative Stress

Dopaminergic Neuron Loss

Show evidence (1 reference)

PMID:35339179 SUPPORT

"The dysregulation of VGCC activity has been reported in both Parkinson's disease (PD) and Huntington's (HD)."

This review establishes the fundamental role of calcium channel dysregulation in PD pathogenesis.

Endoplasmic Reticulum Stress

Accumulation of misfolded proteins in the ER activates the unfolded protein response (UPR). Chronic ER stress overwhelms protective mechanisms, triggering apoptotic pathways. Alpha-synuclein aggregates and GBA mutations directly impair ER function.

Dopaminergic Neuron CL:0000700

ER Stress Response GO:0034976 Unfolded Protein Response GO:0030968

Downstream

Autophagy-Lysosome Pathway Dysfunction

Dopaminergic Neuron Loss

Show evidence (1 reference)

PMID:38026955 SUPPORT

"Accumulating evidence shows that endoplasmic reticulum (ER) stress occurring in the SNpc DA neurons is an early event in the development of PD."

This review establishes ER stress as an early and central event in PD pathogenesis.

Synaptic Dysfunction

Impaired synaptic vesicle recycling, particularly defects in clathrin-mediated endocytosis, represents an early feature of PD. Multiple PD genes (DNAJC6, SYNJ1, LRRK2, ITSN1) regulate synaptic vesicle trafficking, and their dysfunction leads to synaptic failure before overt neurodegeneration. ITSN1 is a scaffold protein that orchestrates clathrin-mediated endocytosis, placing it on this convergent node alongside DNAJC6 and SYNJ1.

Synaptic Vesicle Endocytosis Dysfunction as a Convergent PD Mechanism

Dopaminergic Neuron CL:0000700

DNAJC6 hgnc:15469 SYNJ1 hgnc:11503 ITSN1 hgnc:6183

Synaptic Vesicle Cycle GO:0099504 Synaptic Vesicle Endocytosis GO:0048488

ITSN1 endocytic scaffold adaptor activity GO:0060090 ↓ DECREASED

Downstream

Dopaminergic Neuron Loss

Alpha-Synuclein Aggregation

Show evidence (4 references)

PMID:40056900 SUPPORT BACKGROUND Other

"ITSN1 encodes a multidomain scaffold protein that orchestrates protein-protein interactions during clathrin-mediated endocytosis and synaptic vesicle recycling."

States the clathrin-mediated endocytosis and synaptic-vesicle-recycling role that places ITSN1 on this node. The sentence restates established protein function in the introduction of a human genetics paper, so it is graded OTHER with a BACKGROUND quote role.

PMID:38595283 SUPPORT

"Notably, several of these genes are linked to the synaptic vesicle recycling process, particularly the clathrin-mediated endocytosis pathway. This suggests that impaired synaptic vesicle recycling might represent an early feature of Parkinson's disease"

Establishes synaptic vesicle endocytosis dysfunction as an early feature of PD.

PMID:23804577 SUPPORT BACKGROUND Other

"SYNJ1 encodes synaptojanin 1, a phosphoinositide phosphatase protein with essential roles in the postendocytic recycling of synaptic vesicles."

States the postendocytic synaptic-vesicle recycling role that places SYNJ1 on this node rather than on the mitochondrial node. The sentence restates established protein function in the introduction of a human genetics paper, so it is graded OTHER with a BACKGROUND quote role.

+ 1 more reference

Iron Accumulation and Ferroptosis

Abnormal iron deposition in the substantia nigra promotes ferroptosis, an iron-dependent form of cell death characterized by lipid peroxidation. Iron catalyzes Fenton reactions generating hydroxyl radicals, and dysregulated iron metabolism contributes to oxidative damage.

Dopaminergic Neuron CL:0000700

Iron Ion Homeostasis GO:0006879 Ferroptosis GO:0097707

Downstream

Oxidative Stress

Dopaminergic Neuron Loss

Show evidence (1 reference)

PMID:39218077 SUPPORT

"Parkinson's disease (PD) is a prevalent and advancing age-related neurodegenerative disorder, distinguished by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Iron regional deposit in SNpc is a significant pathological characteristic of PD."

This review establishes iron accumulation as a significant pathological characteristic and mechanistic driver of PD.

Blood-Brain Barrier Dysfunction

Altered tight junction proteins, transporter dysfunction, and alpha-synuclein accumulation compromise BBB integrity. BBB breakdown allows infiltration of peripheral immune cells and blood-borne molecules, amplifying neuroinflammation.

Brain Endothelial Cell CL:2000044 Pericyte CL:0000669 Astrocyte CL:0000127

BBB Maintenance GO:0035633 Vascular Permeability GO:0043114

Downstream

Neuroinflammation

Dopaminergic Neuron Loss

Show evidence (2 references)

PMID:39075566 SUPPORT

"There is increasing evidence for blood-brain barrier (BBB) alterations in Parkinson's disease (PD), the second most common neurodegenerative disorder with rapidly rising prevalence."

This comprehensive 2024 review establishes BBB dysfunction as an emerging mechanism in PD pathogenesis.

PMID:42599550 SUPPORT Other

"As the most abundant glial cells in the central nervous system (CNS), astrocytes may exert neuroprotective effects through mechanisms including secretion of neurotrophic factors, regulation of the blood-brain barrier (BBB), and maintenance of water-electrolyte balance."

Supports the astrocyte among the cell types regulating the barrier, which is why this node carries astrocyte as a cell type.

Metabolic Dysfunction and Weight Loss

Parkinson disease is associated with progressive weight loss and metabolic dysregulation through multiple interacting mechanisms. Reduced metabolic rate, dysregulated appetite-regulating hormones (leptin, ghrelin, GLP-1), gastrointestinal dysfunction, cognitive decline affecting appetite awareness, dopaminergic-medication effects, and dopamine-dependent regulation of feeding behavior all contribute to systemic metabolic failure and weight loss. Weight loss occurs in a substantial fraction of PD patients and exerts significant morbidity and mortality, yet mechanistic understanding remains incomplete.

Metabolic process GO:0008152

Downstream

Weight Loss Metabolic dysregulation, reduced energy expenditure, neuroendocrine hormone imbalances, and gastrointestinal dysfunction converge to cause progressive weight loss and nutritional decline in PD.

Show evidence (1 reference)

PMID:41781031 SUPPORT Other

This 2026 review establishes weight loss as a significant, mechanistically complex, and undertreated symptom of Parkinson disease, establishing the rationale for a dedicated metabolic dysfunction mechanism node.

PP2A Phosphatase Activation Failure

Biallelic PTPA missense variants lower PTPA protein levels and, through that, the level of assembled protein phosphatase 2A complex, so the phosphatase is not activated normally. PP2A is the major serine/threonine phosphatase of the brain, and this node is the molecular step that defines the PARK25 subtype.

PTPA hgnc:9308

protein serine/threonine phosphatase activity GO:0004722 ↓ DECREASED

Downstream

Striatal Dopamine Deficiency The dopaminergic step is an inference rather than a direct measurement: the only functional in vivo result is a levodopa-reversible climbing defect in Drosophila, and the affected patients' motor symptoms responded to levodopa. No human nigrostriatal dopamine measurement is reported for PTPA carriers in the cited work.

Show evidence (2 references)

PMID:36073231 SUPPORT In vitro / ex vivo

"expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation"

Directly states the decreased PP2A complex level and impaired phosphatase activation that this node asserts.

PMID:36073231 SUPPORT BACKGROUND Other

"The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signalling pathways and functions"

Source for describing PP2A as the brain's major serine/threonine phosphatase, which is why the node binds a serine/threonine phosphatase activity term. The sentence is the paper's framing of established biology, not its own result.

Postsynaptic D2/D3 Receptor Occupancy by Agonist Therapy

Striatal postsynaptic D2 and D3 receptors remain available to a directly acting agonist as the nigrostriatal terminal is lost, which is why this class works without requiring surviving neurons to take up and decarboxylate levodopa. This is the receptor-occupancy node that dopamine agonist therapy acts on, not a step in the degeneration itself, so it carries no downstream edge into the disease chain.

DRD2 hgnc:3023 DRD3 hgnc:3024

dopamine D2/D3 receptor activation by an agonist drug GO:0001591 ↑ INCREASED

striatum UBERON:0002435

Show evidence (1 reference)

PMID:9617505 SUPPORT DIRECT REVIEW SYNTHESIS In vitro / ex vivo

"Third, it has full intrinsic activity at dopamine D2 subfamily receptors."

Full agonist activity at the receptor is what lets this class act independently of the failing presynaptic dopamine supply.

⬡

Pathograph

Use Group by to collapse related nodes into one box. Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

Digestive 1

Constipation FREQUENT HP:0002019

Common non-motor symptom

Show evidence (1 reference)

PMID:7845407 SUPPORT

"We investigated the role of anorectal manometry in evaluating constipation and anorectal function in 15 patients with Parkinson's disease (PD) and compared results with those of 9 patients with idiopathic constipation (IC) and 8 control (C) subjects."

This study directly evaluates constipation in PD patients, supporting constipation as a common non-motor symptom.

Head and Neck 1

Hyposmia FREQUENT HP:0004409

Often precedes motor symptoms by years

Show evidence (1 reference)

PMID:24136244 SUPPORT

"Hyposmia, identified as reduced sensitivity to odor, is a common non-motor symptom of Parkinson's disease (PD) that antedates the typical motor symptoms by several years. It occurs in ∼90% of early-stage cases of PD."

This establishes hyposmia as a highly prevalent prodromal symptom that precedes motor symptoms, supporting its importance as an early marker of PD.

Musculoskeletal 1

Rigidity VERY_FREQUENT HP:0002063

Cogwheel or lead-pipe rigidity

Show evidence (1 reference)

PMID:17955331 SUPPORT

"Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."

This confirms rigidity as a cardinal sign of parkinsonism relevant to PD.

Nervous System 14

Resting Tremor VERY_FREQUENT HP:0002322

Classic "pill-rolling" tremor at rest

Show evidence (1 reference)

PMID:17955331 SUPPORT

"Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."

This identifies resting tremor as a cardinal sign used to detect parkinsonism, supporting it as a core PD phenotype.

Bradykinesia VERY_FREQUENT HP:0002067

Slowness of movement, required for diagnosis

Show evidence (1 reference)

PMID:17955331 SUPPORT

"Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."

This lists bradykinesia among the cardinal signs of parkinsonism, supporting its central role in PD.

Postural Instability FREQUENT HP:0002172

Develops in later disease stages

Show evidence (1 reference)

PMID:17955331 SUPPORT

"Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."

This supports postural instability as a cardinal parkinsonian sign captured in PD assessments.

Depression FREQUENT HP:0000716

Show evidence (2 references)

PMID:41301797 SUPPORT

"Depressive symptoms were similar across groups, but in prodromal PD, higher GDS scores were associated with worse UPDRS III scores (p = 0.02), as well as higher freezing and fall scores."

This indicates depressive symptoms are present and clinically relevant in PD, supporting depression as a non-motor phenotype.

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"PD patients reported more depression, especially with sleep problems, which also worsened anxiety. Factors like age, motor symptoms, and sleep disturbances relate to depression, while sleep issues are linked to anxiety."

Records the reported association between sleep disturbance and depression in PD. The quoted sentence is about sleep disturbance in general rather than REM sleep behavior disorder specifically, so it belongs on this phenotype; it makes no claim about cognition and recommends no therapy.

REM Sleep Behavior Disorder HP:5200291

Prodromal non-motor feature that often precedes motor onset by years and correlates with greater motor severity. Results from dysfunction of brainstem motor inhibition circuits during REM sleep.

Show evidence (3 references)

PMID:41301797 SUPPORT Human clinical

"Constipation and REM sleep behavioral disorder were independent correlates of worse motor severity in prodromal and established PD"

This PPMI-cohort study establishes REM sleep behavior disorder as a non-motor feature of both prodromal and established Parkinson disease that independently correlates with greater motor severity.

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"It results from dysfunction of the subcoeruleus and magnocellularis nuclei in the brainstem"

Names the brainstem lesion behind RBD. These nuclei are glutamatergic and glycinergic respectively, not dopaminergic, which is the clinical point of RBD in PD: it reflects non-dopaminergic brainstem degeneration that precedes nigral loss, and so appears in the prodromal phase.

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"Dopamine influences motor and non-motor functions, including cognition, mood, sleep, sensory processes, and autonomic systems"

Records that sleep is among the non-motor functions dopamine influences. Kept deliberately narrow: the sentence states dopamine's range of influence, and does not assert depletion, a mechanism independent of motor circuits, or any claim specific to RBD.

Cognitive Impairment FREQUENT HP:0100543

Course: PROGRESSIVE

Spans mild cognitive impairment (typically executive and visuospatial deficits) through to Parkinson disease dementia; the risk of dementia rises with disease duration.

Show evidence (2 references)

PMID:34210995 SUPPORT Human clinical

"In addition to the defining motor symptoms of PD, multiple non-motor symptoms occur; among them, cognitive impairment is common and can potentially occur at any disease stage."

This Nature Reviews Disease Primers review establishes cognitive impairment as a common non-motor feature of PD that can occur at any disease stage.

PMID:34210995 SUPPORT Human clinical

"executive and visuospatial impairments are typical and can be accompanied by memory impairment, increasing the risk for early progression to dementia"

Describes the mild-cognitive-impairment-to-dementia progression that underpins the progressive clinical course of cognitive impairment in PD.

Excessive Daytime Somnolence HP:0001262

Persistent daytime sleepiness with brief involuntary sleep episodes ('sleep attacks'), often without warning of drowsiness. Associated with increased levodopa doses, sleep apnea, and higher rates of depression, hallucinations, and dementia.

Show evidence (2 references)

PMID:42646502 SUPPORT Human clinical

"Some of these sudden events are referred to as 'sleep attacks,' and they occur without warning of drowsiness"

The review describes excessive daytime sleepiness and sleep attacks as significant non-motor manifestations that impact safety and quality of life in PD.

PMID:42646502 SUPPORT Human clinical

"These patients need more levodopa, often have sleep apnea, and show higher rates of depression, hallucinations, and dementia"

The review links excessive daytime sleepiness to more severe PD phenotypes, including comorbid neuropsychiatric symptoms and the need for higher dopaminergic medication.

Apathy FREQUENT HP:0000741

Lack of motivation and interest, distinct from depression (no sadness). Often related to loss of dopamine and serotonin. May be more bothersome than depression symptoms alone in PD.

Show evidence (2 references)

PMID:42646502 SUPPORT Human clinical

"Apathy is different from depression because it shows no sadness"

The review establishes apathy as a distinct non-motor symptom with different phenomenology than depression, requiring separate clinical attention and treatment approaches.

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"Given the high prevalence of depression, anxiety, and apathy in PD, the goal is to seek tools to manage these aspects of PD."

Supports the frequency recorded on this node rather than the phenotype itself: the review states apathy is highly prevalent in PD, which the phenomenology snippet above does not.

Dystonia HP:0001332

Involuntary sustained or intermittent muscle contractions causing abnormal postures. When present in PD, dystonia is predominantly focal, most commonly affecting the lower limbs, followed by cervical involvement, and is associated with advanced Hoehn and Yahr stage (≥3), younger age at PD onset, and shorter disease duration. A population prevalence of dystonia in PD is not established by the cited case-control study, so no frequency band is asserted.

Show evidence (4 references)

PMID:42430982 SUPPORT Human clinical

"Focal dystonia was the predominant phenotype (75.0%), most commonly involving lower limbs, followed by cervical dystonia."

This clinical study characterizes the somatotopic distribution of dystonia in PD, showing that focal dystonia is the predominant form and lower-limb involvement is most common.

PMID:42430982 SUPPORT Human clinical

"Data on 246 PD patients (164 with and 82 without dystonia) were analyzed."

Describes the case-control study composition (164 PD patients with dystonia versus 82 without, drawn from the same source population). The 164:82 split is the study's case:control sampling ratio, not a population prevalence, and does not by itself quantify how frequently dystonia occurs in PD.

PMID:42430982 SUPPORT Human clinical

"advanced H&Y stage ≥3 (OR, 3.61; P = 0.002) was directly associated with it."

Establishes association between dystonia and advanced Hoehn and Yahr stage, supporting dystonia as a clinical marker of disease progression.

+ 1 more reference

Impulse Control Behaviors OCCASIONAL Impulsivity HP:0100710

Reward-seeking impulse control behaviors (gambling, hypersexuality, compulsive shopping, binge eating) represent a major behavioral comorbidity in PD, particularly in patients receiving dopamine agonist therapy. These behaviors arise from dopaminergic sensitization of reward-processing circuits and are distinct from classic obsessive-compulsive compulsions. Bound to HP:0100710 Impulsivity, which is the closest available HP term; preferred_term carries the more specific clinical concept. What HP lacks is a term for the dopaminergic-therapy-related ICB syndrome as such - one that distinguishes it from trait impulsivity and from HP:0000722 Compulsive behaviors - not a term for impulsivity. The frequency band is OCCASIONAL (5-29%): the meta-analytic point estimate is 19% (95% CI 15-24%) and the DOMINION cross-sectional estimate is 13.6%, so both the pooled estimate and its confidence interval sit inside that band.

Show evidence (4 references)

PMID:20457959 SUPPORT Human clinical

"An ICD was identified in 13.6% of patients (gambling in 5.0%, compulsive sexual behavior in 3.5%, compulsive buying in 5.7%, and binge-eating disorder in 4.3%), and 3.9% had 2 or more ICDs."

Peer-reviewed point-prevalence estimate from 3090 patients at 46 movement disorder centres, with the four constituent behaviors counted separately. Corroborates the preprint meta-analysis and independently places the frequency in the OCCASIONAL band.

PPR:PPR1298507 Preprint · not peer-reviewed SUPPORT Human clinical

"A random-effects meta-analysis of 27 studies (n = 17,906) found a mean event rate for at least one ICB in PD of 0.19 [95% CI = 0.15, 0.24]"

Pooled event rate across 27 studies, giving the 19% (95% CI 15-24%) estimate behind the OCCASIONAL band. A non-peer-reviewed preprint, cited alongside the peer-reviewed DOMINION prevalence above rather than as sole support.

PMID:20457959 SUPPORT Human clinical

"Impulse control disorders were more common in patients treated with a dopamine agonist than in patients not taking a dopamine agonist (17.1% vs 6.9%; odds ratio [OR], 2.72; 95% confidence interval [CI], 2.08-3.54; P < .001)."

Quantifies dopamine agonist exposure as a risk factor for this phenotype, which is the peer-reviewed counterpart of the preprint's qualitative statement below.

+ 1 more reference

Anxiety FREQUENT HP:0000739

Common non-motor symptom manifesting physically (sweating, headaches, sleep issues, racing heart, indigestion) and psychologically (panic attacks, worry, compulsive behaviors). Reported as interacting with fear and limbic circuitry rather than arising only as a reaction to motor disability.

Show evidence (2 references)

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"Anxiety is a common non-motor symptom of PD, not just a reaction. It manifests physically (sweating, headaches, sleep issues, racing heart, indigestion) and psychologically (panic attacks, worry, unease, nervousness, compulsive behaviors)."

This comprehensive review establishes anxiety as a common neuropsychiatric non-motor symptom of PD with both somatic and psychological manifestations.

PMID:42646502 SUPPORT INDIRECT REVIEW SYNTHESIS Other

"Changes in anxiety to changes in hypothesized fear and limbic circuits were reported, suggesting PD neuropathology interacts with these pathways to promote anxiety."

Points to central fear-processing and limbic circuitry in PD anxiety, rather than to depression or a reaction to motor symptoms. The source reports this as a hypothesized circuit correlation, so the quote reaches the claim by an inference step; the same sentence is graded identically on the limbic pathophysiology edge.

Freezing of Gait FREQUENT HP:0031825

Complex motor phenomenon where patients experience sudden inability to initiate or continue walking, often triggered by environmental factors (doorways, narrow spaces, turns, darkness, stress). Involves both motor and non-motor (cognitive, attentional, visuospatial) factors.

Show evidence (1 reference)

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"FOG is a common and complex symptom in PD, involving both motor and non-motor factors. It occurs when PD patients feel as if their feet are glued to the floor, especially at doorways, during turns, in narrow spaces, changing surfaces, in darkness, or under stress."

This review characterizes freezing of gait as a common, multifactorial symptom with motor and non-motor components, describing the contextual triggers and impact on quality of life and fall risk in PD.

Insomnia FREQUENT HP:0100785

Difficulty falling or staying asleep, often with early awakenings, leading to daytime fatigue and reduced quality of life. One of the most common sleep disorders in PD and correlates with cognitive decline and depression. Deliberately left with no incoming causal edge: PMID:42646502 records the frequency and the progression trend but offers no mechanism specific to insomnia, and the nearest candidate in its pathophysiology table ("sleep fragmentation, and sleep disturbances" under serotonergic raphe loss) names a broader sleep phenotype than this node. Wiring it would assert a mechanism the cited source does not.

Show evidence (1 reference)

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"It is the most common sleep disorder in PD, increasing with disease progression."

This review identifies insomnia as the most prevalent sleep disorder in PD, with frequency increasing as disease progresses and linkage to cognitive decline and depression, supporting its importance as a non-motor phenotype.

Hallucinations FREQUENT HP:0000738

Show evidence (1 reference)

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"PD psychosis (PDP) is a common neuropsychiatric condition where PwP experience hallucinations and delusions"

Supports the frequency recorded here: the review calls the syndrome in which hallucinations occur a common neuropsychiatric condition of PD.

Constitutional 1

Fatigue FREQUENT HP:0012378

Common, debilitating non-motor symptom that can occur at any disease stage, even before motor symptoms. A subjective, persistent feeling of tiredness disproportionate to activity and not relieved by rest. Categorized as physical, mental, emotional; central vs. peripheral; and primary vs. secondary (linked to mood or sleep).

Show evidence (3 references)

PMID:42646502 SUPPORT Human clinical

"Fatigue can occur at any stage, even before motor symptoms. It is a subjective, persistent feeling of tiredness or low energy disproportionate to activity and not relieved by rest"

The review emphasizes fatigue as a major quality-of-life concern in PD that is often underrecognized despite occurring across all disease stages.

PMID:42646502 SUPPORT REVIEW SYNTHESIS Human clinical

"Fatigue is a common, debilitating non-motor symptom in PD that reduces quality of life"

Supports the frequency recorded on this node. The phenomenology snippet above establishes what fatigue is in PD and when it appears, not how often.

PMID:42646502 SUPPORT INDIRECT REVIEW SYNTHESIS Human clinical

"The study found that individuals who reported exercising had fewer and milder NMS than those who did not exercise"

The review reports that people with PD who exercised had fewer and milder non-motor symptoms, and names fatigue among the non-motor symptoms that study examined. The result is an aggregate across those symptoms rather than a fatigue-specific effect size, so it bears on this node by inference.

Growth 1

Weight Loss HP:0001824

Course: PROGRESSIVE

Progressive unintentional weight loss is a well-recognized non-motor feature of Parkinson disease, arising from multiple interacting mechanisms (metabolic dysregulation, neuroendocrine/appetite-hormone disruption, gastrointestinal dysfunction, cognitive decline, and medication effects). It carries substantial morbidity and mortality.

Show evidence (1 reference)

PMID:41781031 SUPPORT Other

Establishes weight loss as a long-recognized non-motor symptom of Parkinson disease with substantial clinical impact.

🧬

Genetic Associations

SNCA (Causative)

Gene: SNCA hgnc:11138 gene page relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:9197268 SUPPORT

This landmark 1997 Science paper identified the first SNCA mutations in familial PD with autosomal dominant inheritance, establishing SNCA as a causative gene for Parkinson's disease.

CGGV:assertion_d21593ae-ed10-4442-8167-24f96f917302-2022-05-03T134931.425Z SUPPORT Other

ClinGen classifies the SNCA-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.

LRRK2 (Risk Factor)

Gene: LRRK2 hgnc:18618 gene page relationship_type: CAUSATIVE

Show evidence (3 references)

PMID:19945904 SUPPORT

"The LRRK2 G2019S mutation is the most frequent known cause of familial and sporadic Parkinson's disease."

This systematic review establishes that LRRK2 G2019S is the most common genetic cause of both familial and sporadic PD, supporting its role as the major genetic risk factor.

CGGV:assertion_2728e13a-b95a-4c55-8cba-082260094ecd-2021-05-03T160000.000Z SUPPORT Other

ClinGen classifies the LRRK2-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.

PMID:38750146 SUPPORT Model organism

"Chronic intestinal damage in genetically predisposed male mice promotes α-synuclein aggregation in the substantia nigra, loss of dopaminergic neurons and motor impairment."

Offers a candidate explanation for the incomplete, age-dependent penetrance recorded in the notes above: in human LRRK2 G2019S transgenic mice a prodromal gut-inflammatory insult is what converts the genotype into nigral alpha-synuclein aggregation, dopaminergic loss, and motor impairment, and the effect is restricted to males. Whether the same gene-environment interaction modifies penetrance in human carriers is untested.

PINK1 (Causative)

Gene: PINK1 hgnc:14581 relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:25611507 SUPPORT

This identifies PINK1 mutations in autosomal recessive parkinsonism, supporting its causative role in PD.

CGGV:assertion_1999e6c4-eb15-438a-a4ea-98989112dcbb-2023-01-18T190000.000Z SUPPORT Other

ClinGen classifies the PINK1-Parkinson disease gene-disease relationship as definitive with autosomal recessive inheritance.

GBA1 (Risk Factor)

Gene: GBA1 hgnc:4177 gene page relationship_type: RISK_FACTOR

Show evidence (2 references)

PMID:30097731 SUPPORT

"DLB shares risk loci with AD, in the APOE E4 allele, and with PD, in variation at GBA and SNCA."

This identifies GBA as a genetic risk locus shared with PD, supporting its role as a PD risk factor.

CGGV:assertion_9201c03f-10de-447c-9b84-194f14b549b6-2022-05-03T134810.206Z SUPPORT Other

ClinGen classifies the GBA1-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.

PARK7 (Causative)

Gene: PARK7 hgnc:16369 gene page relationship_type: CAUSATIVE

Show evidence (1 reference)

CGGV:assertion_d79439d2-844b-4ba6-aceb-e6b179eaaa01-2022-06-27T160000.000Z SUPPORT Other

ClinGen classifies the PARK7-Parkinson disease gene-disease relationship as definitive with autosomal recessive inheritance.

PRKN (Causative)

Gene: PRKN hgnc:8607 gene page relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:25611507 SUPPORT

This establishes Parkin (PRKN, formerly PARK2) as a gene mutated in autosomal recessive parkinsonism, supporting its causative role.

CGGV:assertion_6b39c4a0-f6bd-4afc-b2a7-f234eab5a667-2023-01-18T190000.000Z SUPPORT Other

ClinGen classifies the PRKN-Parkinson disease gene-disease relationship as definitive with autosomal recessive inheritance.

VPS35 (Causative)

Gene: VPS35 hgnc:13487 relationship_type: CAUSATIVE

Show evidence (1 reference)

CGGV:assertion_b0e546d6-8a44-4e9d-83aa-f781ec4ec166-2021-11-03T134517.796Z SUPPORT Other

ClinGen classifies the VPS35-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.

CHCHD2 (Causative)

Gene: CHCHD2 hgnc:21645 relationship_type: CAUSATIVE

Autosomal dominant

Show evidence (2 references)

PMID:25662902 SUPPORT Human clinical

"CHCHD2 mutations are associated with, and might be a cause of, autosomal dominant Parkinson's disease."

The authors' own conclusion about the gene-disease relationship, quoted rather than strengthened.

PMID:28589937 SUPPORT Model organism

"The loss of CHCHD2 in Drosophila causes abnormal matrix structures and impaired oxygen respiration in mitochondria, leading to oxidative stress, dopaminergic neuron loss and motor dysfunction with age."

Provides the mitochondrial mechanism that links CHCHD2 loss to dopaminergic degeneration, and is the basis for binding CHCHD2 to the mitochondrial dysfunction node.

PTPA (Causative)

Gene: PTPA hgnc:9308 relationship_type: CAUSATIVE

Autosomal recessive

Show evidence (3 references)

PMID:36073231 SUPPORT Human clinical

"We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability."

Establishes PTPA as a recessive cause and names the biochemical consequence.

PMID:36073231 SUPPORT Human clinical

"We first identified a homozygous PTPA variant, c.893T>G (p.Met298Arg), in patients from a South African family with early-onset parkinsonism and intellectual disability."

Documents the index family and its homozygous genotype.

PMID:37046398 SUPPORT Human clinical

"One patient with early-onset PD from a consanguineous family carried the homozygous variant p.Met329Val, while her parents and elder sister with heterozygous p.Met329Val were healthy."

Independent replication in a cohort of 2743 cases and 8177 controls, with heterozygous relatives unaffected.

VPS13C (Causative)

Gene: VPS13C hgnc:23594 relationship_type: CAUSATIVE

Autosomal recessive

Show evidence (2 references)

PMID:26942284 SUPPORT Human clinical

"This work suggests that loss of function of VPS13C is a cause of autosomal-recessive early-onset parkinsonism with a distinctive phenotype of rapid and severe progression."

Establishes biallelic VPS13C loss of function as a cause of recessive early-onset parkinsonism.

PMID:26942284 SUPPORT In vitro / ex vivo

"Silencing of VPS13C was associated with lower mitochondrial membrane potential, mitochondrial fragmentation, increased respiration rates, exacerbated PINK1/Parkin-dependent mitophagy, and transcriptional upregulation of PARK2 in response to mitochondrial damage."

Cell-model basis for binding VPS13C to the mitochondrial dysfunction node.

SYNJ1 (Causative)

Gene: SYNJ1 hgnc:11503 gene page relationship_type: CAUSATIVE

Autosomal recessive

Show evidence (2 references)

PMID:23804577 SUPPORT Human clinical

Identifies the segregating biallelic SYNJ1 variant and the phenotype.

PMID:23804577 SUPPORT BACKGROUND Other

"SYNJ1 encodes synaptojanin 1, a phosphoinositide phosphatase protein with essential roles in the postendocytic recycling of synaptic vesicles."

States the synaptic-vesicle recycling function that places SYNJ1 on the synaptic dysfunction node. The sentence restates established protein function rather than a finding of this study, so it is graded OTHER with a BACKGROUND quote role.

DNAJC6 (Causative)

Gene: DNAJC6 hgnc:15469 relationship_type: CAUSATIVE

Autosomal recessive

Show evidence (5 references)

PMID:22563501 SUPPORT Human clinical

"Using homozygosity mapping and whole exome sequencing we identified a deleterious mutation in DNAJC6 in two patients with juvenile parkinsonism."

Original identification of DNAJC6 in juvenile parkinsonism.

PMID:22563501 SUPPORT BACKGROUND Other

"DNAJC6 encodes the HSP40 Auxilin, a protein which is selectively expressed in neurons and confers specificity to the ATPase activity of its partner Hcs70 in clathrin uncoating."

States the clathrin-uncoating function that places DNAJC6 on the synaptic dysfunction node. The sentence restates established protein function rather than a finding of this study, so it is graded OTHER with a BACKGROUND quote role.

PMID:26528954 SUPPORT Human clinical

"Our findings delineate a novel form of hereditary early-onset PD."

Extends the DNAJC6 phenotype from juvenile parkinsonism to early-onset Parkinson disease, which is the basis for curating two subtype rows.

+ 2 more references

FBXO7 (Causative)

Gene: FBXO7 hgnc:13586 relationship_type: CAUSATIVE

Autosomal recessive

Show evidence (2 references)

PMID:19038853 SUPPORT Human clinical

Establishes FBXO7 as a recessive cause of the parkinsonian-pyramidal phenotype.

PMID:23933751 SUPPORT In vitro / ex vivo

"Here we show that Fbxo7 participates in mitochondrial maintenance through direct interaction with PINK1 and Parkin and acts in Parkin-mediated mitophagy."

Places FBXO7 in the PINK1/parkin mitophagy pathway, which is the basis for binding it to the mitochondrial dysfunction node.

ITSN1 (Risk Factor)

Gene: ITSN1 hgnc:6183 relationship_type: RISK_FACTOR

Show evidence (2 references)

PMID:40056900 SUPPORT Human clinical

"we discover that protein-truncating variants in ITSN1 confer a substantially increased risk of PD"

Whole-genome sequencing of 3,809 PD cases and 247,101 controls identifies ITSN1 loss-of-function variants as a PD risk factor.

PMID:40056900 SUPPORT Human clinical

"We replicate this association in three independent datasets totaling 8,407 cases and 413,432 controls"

Independent replication of the ITSN1 association.

💊

Medical Actions

Levodopa/Carbidopa

Action: Pharmacotherapy NCIT:C15986

Agent: levodopa CHEBI:15765 carbidopa CHEBI:3395

Gold standard treatment, replaces dopamine precursor.

Mechanism Target:

RESTORES Striatal Dopamine Deficiency — Levodopa supplies dopamine precursor to partially restore dopaminergic signaling in dopamine-depleted striatal circuits.

Show evidence (1 reference)

PMID:27577098 SUPPORT

"The symptomatic treatment of the motor symptoms of Parkinson disease (PD) has been constantly optimized using pharmacotherapy (L-Dopa, several dopamine agonists, inhibitors of monoamine oxidase (MAO)-B and catechol-o-methyltransferase (COMT), and amantadine), deep brain stimulation, and physiotherapy."

This review identifies L-Dopa as a core pharmacotherapy for PD motor symptoms.

Dopamine Agonists

Action: Pharmacotherapy NCIT:C15986

Platform: Small molecule

Directly stimulate dopamine receptors. Carries a class-level risk of impulse control behaviors: dopamine agonist exposure raises the odds of an ICD roughly 2- to 3.5-fold, and the association holds across pramipexole and ropinirole rather than being specific to one agent. See the Impulse Control Behaviors phenotype.

Mechanism Target:

BYPASSES Striatal Dopamine Deficiency — Dopamine agonists bypass reduced endogenous dopamine by directly stimulating dopamine receptors in downstream circuits.

ACTIVATES Postsynaptic D2/D3 Receptor Occupancy by Agonist Therapy — The agonist occupies and activates the postsynaptic receptor directly; the existing BYPASSES edge records the consequence of doing so while presynaptic dopamine is deficient.

Show evidence (2 references)

PMID:27577098 SUPPORT

This review identifies dopamine agonists as part of standard pharmacotherapy for PD.

PMID:20457959 SUPPORT Human clinical

"Dopamine agonist treatment in PD is associated with 2- to 3.5-fold increased odds of having an ICD. This association represents a drug class relationship across ICDs."

Establishes the impulse-control adverse effect as a property of the dopamine agonist drug class rather than of an individual agent, which is why it is recorded on this treatment entry and not only on the phenotype.

Impulse Control Behavior Management

Action: Therapeutic Procedure NCIT:C49236

Management of dopaminergic-therapy-related impulse control behaviors. The first-line step in practice is reduction or withdrawal of the dopamine agonist; the interventions studied beyond that are cognitive behavioural therapy, levodopa infusion, atomoxetine, naltrexone, valproic acid, and deep brain stimulation. The evidence base is small and preliminary - a narrative synthesis of 10 studies totalling 283 patients - so this is recorded as a treatable target rather than as established therapy.

Mechanism Target:

INHIBITS Impulse Control Behaviors — These interventions are studied as ways to reduce impulse control behaviors themselves, which is what connects this phenotype to the treatment graph.

Show evidence (1 reference)

PPR:PPR1298507 Preprint · not peer-reviewed SUPPORT Human clinical

"A narrative synthesis of 10 studies (n = 283) found preliminary evidence for the effectiveness of cognitive behavioural therapy, levodopa infusion, atomoxetine, naltrexone, valproic acid, and deep brain stimulation in supporting ICB reduction."

The source for the intervention list and for the strength of the claim - preliminary evidence from a narrative synthesis, not pooled effect estimates.

MAO-B Inhibitors

Action: Pharmacotherapy NCIT:C15986

Agent: selegiline CHEBI:50217 rasagiline CHEBI:63620

Prevent dopamine breakdown (selegiline, rasagiline).

Mechanism Target:

MODULATES Striatal Dopamine Deficiency — MAO-B inhibitors prolong dopamine signaling by reducing dopamine breakdown.

Show evidence (1 reference)

PMID:27577098 SUPPORT

This review lists MAO-B inhibitors among standard PD pharmacotherapies.

COMT Inhibitors

Action: Pharmacotherapy NCIT:C15986

Agent: entacapone CHEBI:4798

Extend levodopa duration (entacapone).

Mechanism Target:

MODULATES Striatal Dopamine Deficiency — COMT inhibitors extend levodopa-derived dopaminergic signaling and indirectly modulate striatal dopamine deficiency.

Show evidence (1 reference)

PMID:27577098 SUPPORT

This review lists COMT inhibitors among standard PD pharmacotherapies.

Deep Brain Stimulation

Action: deep brain stimulation Ontology label: Deep Brain Stimulation NCIT:C21024

Surgical therapy for advanced motor fluctuations.

Mechanism Target:

MODULATES Basal Ganglia Circuit Dysfunction — DBS modulates abnormal basal ganglia motor circuit activity rather than acting upstream on dopaminergic neuron loss.

Show evidence (1 reference)

PMID:27577098 SUPPORT

This review identifies deep brain stimulation as a standard symptomatic therapy for PD.

Physical Therapy

Action: Physical Therapy NCIT:C15302

Platform: Behavioral / lifestyle

Maintains mobility and reduces fall risk. Exercise programs including PWR!Moves, Rock Steady Boxing, Dance for Parkinson's, yoga, and tai chi are evidence-based approaches that specifically reduce rigidity, improve postural stability, and enhance motor fluidity through rebalancing of basal ganglia circuits.

Mechanism Target:

MODULATES Basal Ganglia Circuit Dysfunction — Structured exercise is reported to shift the excitatory/inhibitory balance within the basal ganglia rather than route around it. Cueing and compensation strategies, which do work around the circuit, are delivered alongside it; MODULATES records the claim this entry actually cites evidence for.

Show evidence (1 reference)

PMID:42646502 SUPPORT REVIEW SYNTHESIS Other

"Exercise helps reestablish the balance between excitatory and inhibitory signals in the basal ganglia, decreasing excitotoxicity and enhancing movement"

Link-level evidence for the mechanism of action asserted by this edge. Graded OTHER with quote_role REVIEW_SYNTHESIS: the sentence is the review's synthesis of its references [305-308] under the heading "Modulation of glutamate and motor circuits", not a result this publication reports.

Show evidence (4 references)

PMID:27577098 SUPPORT

This review lists physiotherapy as part of symptomatic treatment for PD.

PMID:42646502 SUPPORT Human clinical

"Stretching and range-of-motion exercises (e.g., PWR!Moves), strengthening exercises (e.g., Rock Steady Boxing), dancing (e.g., Dance for Parkinson's Disease), and yoga and tai chi help reduce stiffness"

Comprehensive review identifies multiple evidence-based exercise modalities that effectively reduce rigidity and motor stiffness in PD.

PMID:42646502 SUPPORT Human clinical

"Tai Chi was found to be effective, alongside resistance and stretching, for improving motor symptoms, physical abilities, and quality of life in early to mid-stage PD"

Tai Chi demonstrates measurable benefit for multiple motor domains including endurance, control, and postural stability in PD.

+ 1 more reference

Botulinum Neurotoxin A (BoNT/A) for Depression

Action: botulinum toxin type A therapy Ontology label: Botulinum Toxin Therapy NCIT:C157775

Botulinum toxin type A alleviates depression in Parkinson's disease by inhibiting the complement C3-C3aR signaling axis and reducing microglial synaptic phagocytosis. This represents a novel complement-targeted approach to managing depression as a non-motor symptom in PD, distinct from BoNT/A's canonical motor symptom applications.

Mechanism Target:

INHIBITS Complement C3-C3aR Activation in Depression — BoNT/A suppresses complement C3-C3aR signaling through modulation of microglial phagocytosis-related functions, reducing microglial activation and synaptic phagocytosis, thereby alleviating depression-like symptoms in PD models.

Show evidence (1 reference)

PMID:42263400 SUPPORT Model organism

"BoNT/A treatment alleviated depressive-like behaviours and reduced microglial synaptic engulfment in an MPTP model; these therapeutic effects were abolished in C3-/- and C3aR-/- mice."

Mouse PD model demonstrates that BoNT/A alleviates depression-like behavior through inhibition of the C3-C3aR complement axis, preventing microglial synaptic engulfment and protecting against synapse loss in the hippocampus.

🌍

Environmental Factors

Pesticide Exposure

Hazard type: CHEMICAL

Route: UNKNOWN

Duration: CHRONIC

Exposome domain: SPECIFIC EXTERNAL

Rotenone and paraquat are the compounds with the longest-standing link to the disease, but they are a small part of the implicated set: the PEG screen associates 53 active ingredients at FDR 0.05 or below, and 18 of its top 25 remain registered with the US EPA. Treat the per-compound estimates as a ranking of candidates rather than a list of established causes, and do not read the odds ratios as comparable potencies: each is per one standard deviation of its own compound's exposure distribution, so the column is denominated differently on every row. Note also that the paper's top five is ordered by FDR, not by odds ratio, and the two orderings differ. The largest odds ratio in the deposited Fig. 2b table, fluazifop-butyl at 1.260, ranks 32nd of 68 by p and is absent from the top five, because it also carries the table's widest confidence interval, 1.090-1.456. That is an outlier rather than the pattern: the other seven compounds in the top eight by odds ratio all sit within 6% of the median interval width and all rank in the top nine by p. Quote the paper's ordering rather than re-ranking by odds ratio. The same screen shows the exposures are heavily correlated, with 75% of the associated pesticides that either were not individually toxic to neurons or could not be tested correlating at R 0.45 or above with at least one that was, and none of the per-compound models adjust for the others. Dicofol is the most interconnected compound in that correlation network, followed by propargite and methomyl. Two points about the golf-course proximity study (PMID:40338549) that its own Results prose does not make plain. Table 3 uses "vulnerable groundwater with a golf course" as its reference, so the golf-course contrast within vulnerable groundwater regions has to be recovered by inverting the vulnerable-without-a-course row, 0.74 (0.43-1.27), giving 1.35 (0.79-2.33) at p = 0.28. That contrast is null and the paper does not report it. The paper's claim that the largest effect sizes were for a golf course in a vulnerable groundwater region rests instead on comparisons against nonvulnerable strata, 1.82 (1.09-3.03) and 1.92 (1.06-3.45), both of which reproduce exactly on inversion; the sentence reporting the second describes its comparator only as service areas without a golf course, omitting that the row is the nonvulnerable one. Quote that paper's own comparisons with their comparators named. Separately, searches of PubMed for golf-course exposure and parkinsonism, and for golf-course pesticide work generally, found no study reproducing the proximity association outside this cohort: the only other human report is an anecdotal letter describing 19 of 26 patients living within 2 miles of a course (PMID:23280848). Treat the association as unreplicated on the evidence located so far rather than as absent from the literature. The compound-level evidence is uneven. Paraquat and rotenone carry the strongest and most consistent associations; organochlorines are positive on blood-measured exposure but heterogeneous by region; and the association for several compounds depends on whether protective equipment was used, which is evidence that the exposure rather than the farming lifestyle is what matters. Manganese is deliberately not curated here: the metals meta-analysis found no association between manganese and idiopathic Parkinson disease, and manganism is a distinct toxicant parkinsonism rather than a synucleinopathy.

Ambient and occupational exposure to agricultural pesticides raises the risk of the disease. The best-resolved human evidence is a pesticide-wide association study in the Parkinson's Environment and Genes (PEG) case-control study, which tested 288 individual active ingredients against record-based exposure estimates and associated 25 of them at FDR 0.01 or below. The compounds in chemicals are that screen's associated active ingredients, with two exceptions: rotenone and paraquat carry the longest-standing link to the disease but are not hits of this screen, because paraquat dichloride was held out of it and reported separately and rotenone enters only as prior work. The one compound with its own measured mechanism carries its own entry, Trifluralin Exposure.

Show evidence (7 references)

PMID:15177059 SUPPORT

"there is general agreement that smoking and exposure to pesticides affect the probability of developing PD."

This review supports pesticide exposure as an environmental factor influencing PD risk.

PMID:37193692 SUPPORT Human clinical

"Our PWAS implicated 25 pesticides as associated with PD at a meta-analysis FDR ≤ 0.01 (8.7% of all tested pesticides), another 28 at 0.01<FDR ≤ 0.05 (9.7%), and 15 at 0.05<FDR < 0.10 (5.2%)"

Record-based pesticide-wide association study in PEG, 829 patients and 824 controls in three agricultural counties of central California, testing the 288 active ingredients with at least 25 exposed participants. Exposure came from California Pesticide Use Report application records combined with land-use maps in a GIS model, not from self-report. The per-compound odds ratios this screen reports are per one standard deviation of the log-transformed, centred and SD-scaled exposure estimate, pooled across two study waves and two locations by fixed-effects meta-analysis; they are not ever-versus-never contrasts, so the unit has to travel with any quoted figure. Each pesticide's estimate is scaled to its own standard deviation and no per-compound standard deviations are published, so an odds ratio here cannot be converted back to pounds per acre per year, and two compounds' odds ratios are not on a common scale. Models were adjusted for age, sex, race/ethnicity, education and index year, and not for smoking or for co-exposure to the correlated pesticides the same paper maps.

PMID:32919961 SUPPORT Human clinical

"Ever-use of the insecticide terbufos (HR:1.31, 95%CI:1.02-1.68) and the herbicides trifluralin (HR:1.29, 95%CI: 0.99-1.70) and 2,4,5-T (HR:1.57, 95%CI:1.21-2.04) was associated with elevated PD risk."

Agricultural Health Study, a prospective cohort independent of PEG: 38,274 pesticide applicators and 27,836 spouses followed about 20 years, with covariate-adjusted Cox regression on self-reported ever-use of 50 named pesticides, with 491 incident cases. It implicates specific compounds rather than pesticides as a class, and reaches that from a different exposure design than the record-based PEG estimates. The trifluralin interval includes 1.0, so that compound is an elevated point estimate the authors count among their positive findings rather than a conventionally significant result; its weight comes from the independence of the design, not from the interval. The same paper reports higher risk among participants with a history of head injury, which bears on the Head Trauma factor in this entry.

+ 4 more references

Mechanism Target:

TRIGGERS Mitochondrial Dysfunction — Rotenone directly inhibits mitochondrial complex I in the animal model. Human evidence concerns the association of pesticide exposure with Parkinson disease. The rat model also reproduces alpha-synuclein-containing nigral inclusions; this model observation does not establish that pathology as a human consequence of pesticide exposure.

Show evidence (2 references)

PMID:11100151 SUPPORT Model organism

"We report that chronic, systemic inhibition of complex I by the lipophilic pesticide, rotenone, causes highly selective nigrostriatal dopaminergic degeneration that is associated behaviorally with hypokinesia and rigidity"

Names the pesticide, the complex I inhibition this node holds, and the nigrostriatal degeneration downstream of it. Rat work, so it carries the mechanism without establishing it in human disease. The animal-model evidence does not by itself establish pesticide-induced mitochondrial pathology or nigral inclusions in human disease.

PMID:15177059 SUPPORT Other

"there is general agreement that smoking and exposure to pesticides affect the probability of developing PD."

Review reporting general agreement that pesticide exposure affects the probability of developing the disease. It establishes the exposure at the level of the disease and says nothing about mitochondria.

TRIGGERS Nigral Cellular Senescence — Paraquat is the one compound in this entry with a measured senescence mechanism. It induces senescence and a secretory phenotype in astrocytes in culture and in mouse brain, and clearing the senescent cells it generates protects the nigral dopaminergic population. The human arm of this exposure is the epidemiological association only; the senescence mechanism is mouse and cell-culture work.

Show evidence (2 references)

PMID:29386135 SUPPORT DIRECT Model organism

"Additionally, PQ was found to induce astrocytic senescence and an SASP in vitro and in vivo, and senescent cell depletion in the latter protects against PQ-induced neuropathology."

Names the exposure, the astrocytic senescence this edge asserts, and the depletion experiment showing the senescent cells matter for the resulting neuropathology. Cell culture and mouse, so the mechanism is not established for human paraquat exposure.

PMID:29386135 SUPPORT INDIRECT Model organism

"Similar to astrocytes in human PD tissues, astrocytes from PQ-treated mice also displayed significant loss of nuclear lamin B1 and HMGB1 (high mobility group box 1), the latter necessary for SASP initiation"

The marker comparison tying the exposure model to the human tissue finding: paraquat reproduces in mouse astrocytes the lamin B1 and HMGB1 loss seen in parkinsonian nigral astrocytes. Indirect, because matching markers in a toxicant model is not evidence that paraquat caused the human changes.

Trifluralin Exposure

Hazard type: CHEMICAL

Route: UNKNOWN

Duration: CHRONIC

Exposome domain: SPECIFIC EXTERNAL

The dose and duration of each experiment are stated in the evidence explanations because EvidenceItem has no slot for them; see issue #15581. The co-exposure result from the same paper, in which trifluralin with tribufos at 10 µM produced a 65% decrease in neuron count against 32% and 8% for the compounds alone, is not recorded as a separate claim: the combination arm ran 6 to 7 wells per combination against 117 control wells, and one pair in the same matrix came out less toxic than trifluralin alone.

Trifluralin is a dinitroaniline herbicide, still registered in the United States, that carries its own entry because it is the one compound from the PEG screen taken through to a measured lesion in human cells. A human induced-pluripotent-stem-cell midbrain dopaminergic culture shows where it acts: a dose-dependent loss of reserve respiratory capacity with basal ATP output held, alongside preferential loss of complex I and complex IV subunits. Two cohorts with different exposure designs, PEG and the Agricultural Health Study, put the exposure in the same direction, but the Agricultural Health Study interval includes no effect, so the epidemiology is consistent rather than settled. The cell work is also acute and high-dose against a chronic low-dose human exposure, so neither layer establishes the other on its own.

Show evidence (2 references)

PMID:32919961 SUPPORT Human clinical

Agricultural Health Study, 38,274 applicators and 27,836 spouses, about 20 years of follow-up, 491 incident cases, covariate-adjusted Cox regression on self-reported ever-use. The interval on the hazard ratio of 1.29 includes 1.0, so this is an elevated point estimate the authors count among their positive findings, not a conventionally significant result, and it should not be cited as a cohort confirming trifluralin without the interval. What it does carry is independence: disjoint authors from the PEG group, self-reported ever-use rather than a GIS exposure model, and different outcome ascertainment, all pointing the same direction. It is also the prior association the source paper gives as its reason for following this compound.

PMID:37193692 SUPPORT In vitro / ex vivo

"Ten PWAS pesticides led to cell death >3 standard deviations above the DMSO control mean at a concentration of 30 µM: propargite, copper sulfate (basic and pentahydrate), dicofol, folpet, naled, endothall, trifluralin, endosulfan, and diquat dibromide"

Live count of TH-tdTomato-positive neurons at day 11 in iPSC-derived midbrain dopaminergic cultures, screening 39 of the PWAS-associated pesticides over a four-point dose curve. Trifluralin is one of the ten entries, all of which were also toxic at 6 µM. Two controls bound how far this goes: five of the ten showed no substantial toxicity in a cardiomyocyte counter-screen, which is the argument for dopaminergic selectivity, and the hits reproduced in a line with SNCA corrected to two wild-type copies, so the toxicity does not depend on an alpha-synuclein background.

Mechanism Target:

TRIGGERS Mitochondrial Dysfunction — Trifluralin removes the respiratory reserve of human dopaminergic neurons without lowering their resting ATP output, and depletes complex I and complex IV subunits more than the other three complexes. This is a narrower claim than the rat rotenone work that otherwise carries this node, and it is made in human cells, but it is an acute high-dose exposure and so does not by itself establish the lesion as the consequence of chronic agricultural exposure. The route into alpha-synuclein is deliberately not claimed: two weeks of a sublethal dose produced no change in phosphorylated alpha-synuclein, recorded below as a refutation.

Show evidence (4 references)

PMID:37193692 SUPPORT In vitro / ex vivo

"We measured mitochondrial subunit abundance after 24 h exposure to 30 µM trifluralin in 3 biological replicates and demonstrated a 50% reduction of Complex I (NDUFB8) and Complex IV (COX II) when compared to DMSO treated controls"

Western blot in SNCA-triplication iPSC-derived midbrain dopaminergic neurons, 30 µM for 24 hours, n=3. The deposited source data give complex I at 49.1% and complex IV at 57.4% of control, so the stated 50% reduction is accurate for complex I and generous for complex IV. The claim recorded here is preferential loss rather than sparing of the rest: the deposited values also fall for SDHB (65.5%), ATP5A (81.6%), UQCRC2 (87.2%) and SDHA (88.7%), and every one of the six falls in all three replicates. The paper's statement that the other complexes show no significant change is a statement about significance at n=3, not an absence of effect.

PMID:37193692 SUPPORT In vitro / ex vivo

"The respiratory capacity of differentiated neurons was reduced to 9% when cells were treated with trifluralin at 90 µM, 26% at 60 µM, and 72% at 30 µM trifluralin compared to DMSO control, with the highest two doses being significantly different from DMSO control"

Mito Stress respirometry, 6 hours, n=3. These are spare respiratory capacity as a percentage of DMSO control, so 90 µM is a reduction of about 91%, not to a 9% reduction. The quoted figures are means of the per-replicate ratios; aggregating as a ratio of means instead gives 9.4%, 25.9% and 74.0%, which is why a recomputation from the deposited data does not land exactly on the published numbers. The specific point for this node is the dissociation: across the same doses ATP production ran at 112.9%, 113.1% and 103.9% of control, so reserve capacity collapsed while resting output was maintained or slightly raised. Only the 60 and 90 µM reductions are significant.

PMID:31973855 SUPPORT In vitro / ex vivo

"trifluralin can disturb the mitochondrial respiration, especially at the highest concentration, but it cannot induce oxidative stress"

Independent group, and a different species, tissue and preparation: mitochondria isolated from rat liver and then dosed in suspension, so this is a biochemical assay outside an organism rather than animal exposure. It supports the respiratory half of this link in a second system, and it matters for the node this entry conforms to: the node bundles complex I inhibition with oxidative stress, and here a group that assayed oxidative stress from trifluralin reports not finding it. Paul et al. assayed no reactive oxygen species in the dopaminergic neurons, so neither study leaves an oxidative-stress claim standing for this compound.

+ 1 more reference

Chlorpyrifos Exposure

Curated separately from the general pesticide entry because its reported mechanism is distinct. The human exposure assessment is long-term residential proximity, not occupational handling.

Show evidence (1 reference)

PMID:41382278 SUPPORT Human clinical

"RESULTS: Long-term residential exposure to CPF was associated with more than a 2.5-fold increased risk of developing PD."

The human arm of the study, a case-control analysis of 829 patients and 824 controls, gives the residential exposure association.

Mechanism Target:

TRIGGERS Autophagy-Lysosome Pathway Dysfunction — Chlorpyrifos is the one implicated pesticide whose experimental mechanism is reported as autophagic rather than mitochondrial. In zebrafish the dopaminergic loss it causes is attributed to impaired autophagic flux together with synuclein accumulation, and is reversed by restoring flux or by removing synuclein. The human arm of the same study is a residential exposure association and does not measure autophagy, so the mechanism is carried by the animal and cell work alone.

Show evidence (1 reference)

PMID:41382278 SUPPORT Model organism

"Using ZF, we found that CPF-induced dopaminergic neuron loss was at least partially due to autophagy dysfunction and synuclein accumulation, as knocking down LC3 recapitulated the dopaminergic neuron loss and restoring autophagic flux or eliminating synuclein reduced neuronal vulnerability."

The rescue experiments are what make this an autophagy claim rather than a correlation: restoring flux reduces the loss, and knocking down LC3 reproduces it. Zebrafish work, so it establishes the route in the model and not in human disease.

Trichloroethylene Exposure

Show evidence (1 reference)

PMID:37184848 SUPPORT Human clinical

"No excess risk was found for other forms of neurodegenerative parkinsonism."

The negative result for other parkinsonian syndromes in the same cohort. It is the reason this exposure is curated on this entry and not on the multiple system atrophy or dementia with Lewy bodies entries.

Mechanism Target:

PREDISPOSES Dopaminergic Neuron Loss — Service at a base whose water supply carried trichloroethylene at many times the permissible concentration is followed by a raised risk of the disease decades later. Pointed at the core lesion rather than at a mechanism node because the cohort study measures incidence only and no cited sentence follows the solvent to any particular step. The same study found no excess of other parkinsonian syndromes, which argues the association is specific to this disease rather than to parkinsonism generally.

Show evidence (1 reference)

PMID:37184848 SUPPORT Human clinical

"In multivariable models, Camp Lejeune veterans had a 70% higher risk of PD (odds ratio, 1.70; 95% CI, 1.39-2.07; P < .001)."

Cohort of 158,122 veterans with exposure data and 430 cases. It quantifies the exposure-disease association and not the neuronal loss this link targets.

Ambient Fine Particulate Matter

The study also reported associations for nitrogen dioxide and for ozone, which are separate pollutants rather than size fractions of this one and are not curated here.

Show evidence (1 reference)

PMID:30124852 SUPPORT Human clinical

"Each interquartile increment (3.8 µg/m3) of PM2.5 was associated with a 4% increase in incident PD (95% confidence interval, 1.01-1.08) after adjusting for various covariates."

The cohort association between fine particulate matter and incident disease.

Mechanism Target:

PREDISPOSES Dopaminergic Neuron Loss — A small increase in incidence per increment of fine particulate matter in a large population cohort. Pointed at the core lesion rather than at neuroinflammation, which is the usual proposal and which this entry holds a node for, because the cohort study measures incidence and nothing in it measures an inflammatory route. The effect is small and its lower confidence bound is close to unity, so it should not be read as a strong risk factor.

Show evidence (1 reference)

PMID:30124852 SUPPORT Human clinical

"Each interquartile increment (3.8 µg/m3) of PM2.5 was associated with a 4% increase in incident PD (95% confidence interval, 1.01-1.08) after adjusting for various covariates."

Population cohort of about 2.2 million adults with 38,745 incident cases. It gives the exposure-incidence association; the interval's lower bound of 1.01 is the reason the description declines to call this strong.

Lead Exposure

Recorded here partly for what it rules out. The same meta-analysis found no association for the other metals it examined, and reported copper, iron and zinc as lower in cases than controls, which is more readily explained as a consequence of the disease than as a cause of it. Manganese was null for idiopathic Parkinson disease, so manganese parkinsonism is not curated on this entry.

Show evidence (1 reference)

PMID:37022311 SUPPORT Human clinical

"We did not find associations between other metals and PD."

The null result for metals other than lead. Curated as evidence in its own right so the entry distinguishes a metal that was studied and found null from one that was never studied.

Mechanism Target:

PREDISPOSES Dopaminergic Neuron Loss — Cumulative lead measured in bone, which indexes lifetime rather than recent exposure, is associated with raised risk. Pointed at the core lesion because the meta-analysis measures risk and not any mechanistic step. Lead is the only metal this meta-analysis found positive.

Show evidence (1 reference)

PMID:37022311 SUPPORT Human clinical

"Cumulative lead levels in bone were found to be associated with increased risk of PD."

Meta-analysis of 83 case-control and 5 cohort studies. Bone lead is a cumulative measure, which matters because a blood measurement taken after diagnosis could reflect the disease rather than precede it.

Dairy Consumption

Left unbound because ECTO has no class at the level this finding is reported. Searched the EBI Ontology Lookup Service for dairy, milk, cheese and yogurt: every ECTO exposure class returned is a specific product, and the milk and cheese and yogurt children are graded by fat content, so binding one of them would assert a fat stratum. That stratum is the thing this meta-analysis specifically does not single out, since it reports raised risk for low-fat dairy as well as for dairy overall. The only term carrying the word dairy is exposure to dairy-based coffee drink via ingestion, which is a different exposure. The same meta-analysis found legumes and nuts protective.

Show evidence (1 reference)

PMID:41252180 SUPPORT Human clinical

"High consumption of dairy, low-fat dairy, and milk demonstrated 26% (odd ratio [OR], 1.26; 95% CI, 1.12-1.41), 30% (OR, 1.30; 95% CI, 1.06-1.58), and 23% (OR, 1.23; 95% CI, 1.07-1.43) increased PD risk compared with the lowest intake categories, respectively."

The pooled prospective association between dairy intake and disease risk.

Mechanism Target:

PREDISPOSES Dopaminergic Neuron Loss — High dairy and milk intake is associated with a modestly raised risk in pooled prospective cohorts, with a dose gradient per cup of milk per day and a stronger association in men. Pointed at the core lesion because the meta-analysis is dietary epidemiology with no mechanistic arm. Dairy is often discussed as a vehicle for pesticide residues or as acting through urate, but nothing cited here measures either route.

Show evidence (1 reference)

PMID:41252180 SUPPORT Human clinical

Meta-analysis of 29 prospective cohorts totalling 1,307,337 participants. Prospective design addresses the reverse-causation objection that weakens case-control dietary studies.

Helicobacter pylori Infection

Recorded with its nulls, which are the more informative half of this literature: the same meta-analysis tested a long list of common infections and found them unrelated to risk, so the positive findings are not a general effect of having been infected with something.

Show evidence (1 reference)

PMID:32017453 SUPPORT Human clinical

"Influenza virus, herpes virus, hepatitis B virus, scarlet fever, mumps virus, chicken pox, pertussis, German measles, and measles were not associated with PD risk."

The null results for nine common infections, curated so the entry distinguishes infections that were studied and found unrelated from infections nobody has examined. Influenza in particular has a long history of being proposed as a cause of parkinsonism.

Mechanism Target:

PREDISPOSES Intestinal Inflammation and Barrier Dysfunction — Gastric infection with Helicobacter pylori is the strongest of the infectious associations in the pooled analysis. Pointed at intestinal inflammation and barrier dysfunction as the node the exposure plausibly acts through, with the intermediates left unknown because the meta-analysis is seroprevalence and risk and measures no mucosal or barrier endpoint. The direction of causation is not settled by these data: gastrointestinal dysfunction is itself an early feature of the disease.

Show evidence (1 reference)

PMID:32017453 SUPPORT Human clinical

"Helicobacter pylori (HP; pooled OR = 1.653, 1.426-1.915, p < .001), hepatitis C virus (HCV; pooled OR = 1.195, 1.012-1.410, p = .035), Malassezia (pooled OR = 1.694, 1.367-2.100, p < .001), and pneumoniae (pooled OR = 1.595, 1.020-2.493, p = .041) infection were associated with increased PD risk."

Meta-analysis of 23 studies. It gives the infection-disease association and does not measure the intestinal barrier this link targets.

Hepatitis C Virus Infection

Left unbound. The only hepatitis C class in ECTO is exposure to Hepatitis C virus HCV-476, which names a single isolate, and the EBI Ontology Lookup Service returns no generic hepatitis C or hepacivirus exposure class, so binding it would assert a strain that the meta-analysis does not distinguish. Searched for hepatitis; the other hits are hepatitis B and hepatitis E, and hepatitis B is null for this disease, which is curated beside the Helicobacter pylori record above. Exposure to virus, ECTO:3000001, is a true parent and is already bound elsewhere in this knowledge base, but it names no organism and so would ground the record at a level that distinguishes nothing; the Helicobacter pylori record beside this one carries a species-level term, and an unbound record is a smaller loss than an inconsistent pair.

Show evidence (1 reference)

PMID:32017453 SUPPORT Human clinical

"CONCLUSION: Patients with infection of HP, HCV, Malassezia, pneumoniae might be an increased risk of PD. Antiviral treatment of HCV could reduce the risk of PD."

The authors' own summary, which states both the association and the treatment effect that this entry curates as separate evidence items.

Mechanism Target:

PREDISPOSES Dopaminergic Neuron Loss — Chronic hepatitis C infection carries a modestly raised risk in the same pooled analysis that reports the Helicobacter pylori association, and the interval's lower bound is close to unity, so the association is weak taken on its own. What makes it worth curating separately is the treatment arm: risk was lower among infected patients who received antiviral treatment than among those who did not, which is the closest thing in this literature to removing the exposure and watching the risk fall. Pointed at the core lesion rather than at neuroinflammation, which is the usual proposal for a systemic viral route and which this entry holds a node for, because nothing in the meta-analysis measures an inflammatory or central endpoint.

Show evidence (2 references)

PMID:32017453 SUPPORT Human clinical

The hepatitis C odds ratio, quoted in the sentence that carries all four positive infection results because they share one clause. Its lower bound of 1.012 is why the description declines to call this strong.

PMID:32017453 SUPPORT Human clinical

"After antiviral treatment against HCV reduced the risk of PD in patients with HCV infection (OR = 0.672, 0.571-0.791, p < .001)."

The treatment arm, which bears on direction of causation in a way the prevalence comparison cannot: treated and untreated patients are both infected, so the contrast is not between infected and uninfected people. It is still observational, and patients selected for antiviral treatment differ from those who are not.

Truncal Vagotomy

No ECTO term binds this exposure. Searched the committed ECTO cache and the EBI Ontology Lookup Service for vagotomy, vagus, vagal and surgical denervation, and none of those queries returned an exposure class; the nearest concepts in ECTO are chemical and environmental agents rather than surgical procedures, so the entry is deliberately left unbound rather than forced onto a broader term.

Show evidence (1 reference)

PMID:26031848 SUPPORT Human clinical

"Statistical precision of risk estimates was limited."

The authors' own statement of the study's main limitation, quoted so the entry does not present the twenty-year hazard ratio as a firm result.

Mechanism Target:

PROTECTS_AGAINST Vagal-Brainstem Alpha-Synuclein Propagation — Surgically cutting the vagal trunk is the closest thing in the human literature to an experimental test of vagal propagation, because it interrupts exactly the anatomical route this node describes. Risk after full truncal vagotomy was lower than in the general population at more than twenty years of follow-up, while selective vagotomy, which spares the trunk, showed no such reduction. The contrast between the two operations is what makes this informative about the route rather than about surgery.

Show evidence (2 references)

PMID:26031848 SUPPORT Human clinical

"Risk of PD was also decreased after truncal vagotomy when compared to the general population cohort (overall adjusted HR = 0.85; 95% CI: 0.63-1.14; follow-up >20 years, adjusted HR = 0.53; 95% CI: 0.28-0.99)."

Danish registry cohort. The headline protective figure is the twenty-year subgroup and its interval only just excludes unity; the overall estimate includes it. The authors state the precision limit themselves, which is why this link is curated as suggestive rather than established.

PMID:26031848 SUPPORT Human clinical

"In patients who underwent superselective vagotomy, risk of PD was similar to the general population (HR = 1.09; 95% CI: 0.84-1.43; follow-up of >20 years: HR = 1.16; 95% CI: 0.80-1.70)."

The comparison operation. Selective vagotomy leaves the vagal trunk intact and carries no risk reduction, which is the control that makes the truncal result bear on the propagation route specifically.

Cigarette Smoking

Curated as a protective association rather than a protective mechanism. The effect direction reverses in isolated REM sleep behaviour disorder, where smoking is a risk factor, and is null in dementia with Lewy bodies; those results are curated on their own entries and are the reason this exposure must not be propagated across the synucleinopathies.

Show evidence (1 reference)

PMID:26272284 SUPPORT Human clinical

"The pooled RR of PD was 0.59 (95% CI, 0.56-0.62) for ever smokers compared with never smokers."

The pooled inverse association between ever having smoked and the disease.

Mechanism Target:

PROTECTS_AGAINST Dopaminergic Neuron Loss — The inverse association between smoking and this disease is among the most reproducible findings in its epidemiology, and is reported with a dose-response relationship. Pointed at the core lesion because the pooled analysis measures risk and no cited sentence follows nicotine to any mechanistic step. Whether the association is protective at all remains disputed: reverse causation, in which a prodromal personality change makes people less likely to take up or continue smoking, is the standing alternative explanation and is not excluded by these data.

Show evidence (1 reference)

PMID:26272284 SUPPORT Human clinical

"The pooled RR of PD was 0.59 (95% CI, 0.56-0.62) for ever smokers compared with never smokers."

Meta-analysis of 61 case-control and 8 cohort studies. It gives the inverse association and does not establish a protective mechanism.

Caffeine Consumption

Show evidence (1 reference)

PMID:32580456 SUPPORT Human clinical

"The individuals in the healthy cohort with regular caffeine consumption had a significantly lower risk of PD during follow-up evaluation (hazard ratio (HR) = 0.797, 95% CI = 0.748-0.849, p < 0.001)."

The prospective inverse association between regular caffeine intake and incidence.

Mechanism Target:

PROTECTS_AGAINST Dopaminergic Neuron Loss — Regular caffeine intake is associated with lower incidence in prospective follow-up of healthy cohorts. Pointed at the core lesion because the pooled analysis measures incidence; adenosine A2A receptor antagonism is the usual proposed route and nothing cited here measures it. As with smoking, reverse causation is a live objection, since reduced caffeine intake can itself be a prodromal feature.

Show evidence (1 reference)

PMID:32580456 SUPPORT Human clinical

Meta-analysis of 13 studies. The estimate is taken from the healthy cohort arm, which is the one that bears on incidence rather than on progression in established disease.

Rural Living

Left without a mechanism link deliberately. Rural living, well-water drinking and farming are proxies for an unidentified exposure rather than exposures in their own right, and the most careful assessment of this literature concludes that the quantitative support for them is inconsistent even though the pesticide associations they are supposed to stand for are not. Linking a proxy to a mechanism node would assert a route that the cited work explicitly declines to support. No ECTO term binds this exposure either. Searched the EBI Ontology Lookup Service for rural, well water, farming and agricultural, and none returned a class covering residence: exposure to farm, which this work added for isolated REM sleep behaviour disorder, names an occupational setting and is narrower than the rural-living and well-water composite this record describes.

Show evidence (3 references)

PMID:11437458 SUPPORT Human clinical

"Our findings suggest that living in a rural area, drinking well water, farming, and exposure to pesticides may be a risk factor for developing PD."

The classic meta-analysis that established these composite proxies as candidate risk factors.

PMID:27055126 REFUTE Human clinical

"In contrast, associations between PD and rural living, well-water consumption, farming and the use of pesticides, herbicides, insecticides, fungicides or paraquat were less consistent when assessed quantitatively or qualitatively."

A weight-of-evidence assessment that used the smoking association as a positive control and found the rural and farming associations inconsistent by comparison. Graded REFUTE against the proxy being an established risk factor; it does not refute the compound-specific pesticide findings curated above, which rest on exposure-assessed studies rather than on residence.

PMID:15177059 SUPPORT

"While clear links to rural living, dietary factors, exposure to metals, head injury, and exposure to infectious diseases during childhood have not been established, there is general agreement that smoking and exposure to pesticides affect the probability of developing PD."

This review notes that clear links to rural living are not established, indicating mixed evidence for this risk factor.

Head Trauma

No ECTO term binds this exposure. Searched the committed ECTO cache and the EBI Ontology Lookup Service for head, trauma, injury and concussion, and none of those queries returned an exposure class, so the entry is left unbound rather than forced onto an unrelated term. The two meta-analyses cited disagree, and the disagreement tracks study design rather than exposure definition.

Show evidence (2 references)

PMID:36781627 SUPPORT

"The risk ratio of TBI among PD and controls by a combination of 15 studies using a random-effect model was 1.48 (95% CI 1.22-1.74)."

This meta-analysis supports head trauma (TBI) as a risk factor for developing PD.

PMID:30396335 REFUTE Human clinical

"However, analyses of individual diagnoses found no evidence that the risk of Alzheimer's disease, and Parkinson's disease in individuals with previous TBI compared to those without TBI."

The population-based null, curated beside the positive meta-analysis so the entry records a contested association rather than a settled one.

Mechanism Target:

PREDISPOSES Dopaminergic Neuron Loss — Traumatic brain injury raises later risk of the disease by about half again. Pointed at the core neuropathological lesion rather than at a mechanism node because no cited sentence follows the injury to any particular step: neuroinflammation is the usual proposal and this entry holds a node for it, but nothing here measures that route, so the intermediates stay unknown. The evidence is also not consistent: a population-based meta-analysis found the association for dementia but not for this disease, so the link is curated with both results.

Show evidence (2 references)

PMID:36781627 SUPPORT Human clinical

"The risk ratio of TBI among PD and controls by a combination of 15 studies using a random-effect model was 1.48 (95% CI 1.22-1.74)."

Meta-analysis of 15 studies giving a risk ratio of 1.48 for traumatic brain injury. It quantifies the exposure-disease association and not the neuronal loss this link targets.

PMID:30396335 REFUTE Human clinical

"However, analyses of individual diagnoses found no evidence that the risk of Alzheimer's disease, and Parkinson's disease in individuals with previous TBI compared to those without TBI."

Meta-analysis restricted to population-based studies, covering 3,263,207 patients across 18 studies, which found injury associated with dementia overall but not with this disease specifically. Restricting to population-based designs removes the referral and recall bias that inflates hospital-based case-control estimates, so this null is the reason the link is PREDISPOSES rather than TRIGGERS.

🔬

Biochemical Markers

Urine bis(monoacylglycerol)phosphate (BMP) isoforms

Context: Urine BMP isoforms serve as accessible biomarkers for Parkinson's disease, with genetic variation in LRRK2 and GBA1 loci significantly modulating their levels. BMP is a lysosomal lipid that accumulates in cells with impaired autophagy-lysosomal pathway function, making it a proxy marker for lysosomal dysfunction in PD.

Show evidence (1 reference)

PPR:PPR1273884 Preprint · not peer-reviewed SUPPORT Human clinical

"We conﬁrm strong associations between urine bis(monoacylglycerol)phosphate (BMP) isoforms and the variants LRRK2 p.G2019S and GBA1 p.N370S"

PPMI GWAS confirms that urine BMP isoforms are modulated by LRRK2 and GBA1 variants and represent a genetically-influenced biomarker for PD, supporting lysosomal dysfunction as a measurable biological marker.

Cerebrospinal fluid (CSF) amyloid-beta (Aβ)

Context: CSF Aβ levels are modulated by APOE ε4 allele status and show complex associations with α-synucleinopathies. Lower CSF Aβ in PD may reflect concurrent amyloid pathology or altered CSF clearance, providing a quantitative readout of amyloid metabolism that is genetically influenced.

Show evidence (1 reference)

PPR:PPR1273884 Preprint · not peer-reviewed SUPPORT Human clinical

"CSF Aβ was signiﬁcantly associated with an APOE ε4 allele, reinforcing its central role in amyloid regulation."

PPMI GWAS shows that CSF Aβ levels are genetically modulated by APOE status, with the ε4 risk allele influencing amyloid metabolism in PD cohorts.

Cerebrospinal fluid (CSF) ceramide isoforms

Context: CSF ceramides are sphingolipids involved in lysosomal function and autophagy, with genetic variants at MCF2L2 and GMNN loci influencing their levels. Ceramide accumulation reflects impaired lysosomal lipid degradation and provides a direct readout of autophagy-lysosomal pathway dysfunction.

Show evidence (1 reference)

PPR:PPR1273884 Preprint · not peer-reviewed SUPPORT Human clinical

"Novel associations were detected between CSF ceramide isoforms the MCF2L2 and GMNN loci"

PPMI GWAS identifies novel genetic associations between CSF ceramide isoforms and MCF2L2/GMNN loci, implicating these loci in lysosomal lipid metabolism dysregulation in PD.

Cerebrospinal fluid (CSF) tau

Context: CSF tau levels, including total tau and phosphorylated tau, show complex associations with PD and are influenced by genetic variation at the TP63 locus. These tau biomarkers reflect both shared amyloid-tau pathology with Alzheimer's disease and PD-specific tau dysregulation.

Show evidence (1 reference)

PPR:PPR1273884 Preprint · not peer-reviewed SUPPORT Human clinical

"between CSF tau and the TP63 locus"

PPMI GWAS identifies a novel genetic association between CSF tau and the TP63 locus, suggesting TP63-mediated pathways influence tau metabolism or clearance in PD.

Lysosomal lipid biomarkers

Context: Multiple lysosomal lipid biomarkers (including ceramides, lactosylceramides, and sphingomyelins) are collectively associated with multiple PD risk loci (MAPT, SIPA1L2, MCCC1, RAB29). This locus-level convergence on a single lipid class is read as pathway-level evidence implicating autophagy-lysosomal clearance, rather than as a measured direction of change in PD.

Show evidence (1 reference)

PPR:PPR1273884 Preprint · not peer-reviewed SUPPORT Human clinical

"Multiple PD risk loci, including MAPT, SIPA1L2, MCCC1, and RAB29, were associated with lysosomal lipid biomarkers"

PPMI GWAS shows that multiple established PD risk loci converge on lysosomal lipid biomarker dysregulation, suggesting that impaired lysosomal function is a shared mechanism across genetically heterogeneous PD and providing biomarker evidence for pathway-level convergence.

🔬

Diagnosis

Motor Severity Rating (UPDRS)

The Unified Parkinson's Disease Rating Scale (UPDRS), and its Movement-Disorder-Society-sponsored revision (MDS-UPDRS), are the clinician-administered instruments for rating motor and non-motor severity in PD. Hoehn and Yahr staging is modeled separately in the stages: section above, using the original five-stage scale.

clinical assessment NCIT:C124351

UPDRS LOINC:77717-7

No reference_ranges band is recorded: UPDRS's individual item codes (Posture, Speech, Gait - parkinsons, Rigidity Neck, Depression scale, etc.) all resolve in LOINC but are never reproduced here. A LOINC code for the original (unmodified) Hoehn and Yahr stage was searched for and not found. Monarch KG queries run against api-v3.monarchinitiative.org/v3/api/search: "Hoehn" returns total: 0, "Hoehn and Yahr" returns total: 0, and "parkinson stage" returns total: 0; "Hoen" returns total: 1, LOINC:77714-4 Modified Hoen and Yahr stage [UPDRS]. That code asserts the modified 0.5-increment Hoehn and Yahr scale, which this entry does not use: the stages: section above carries the original five-stage scale, and PMID:15372591 (the MDS Task Force report, already cited there) recommends that, absent clinimetric validation of the modified version, "the original five-point scales should be maintained." LOINC:77714-4 is therefore left unbound rather than bound against evidence this entry does not support.

Show evidence (2 references)

PMID:19025984 SUPPORT Human clinical

"Movement disorder specialists and study coordinators administered the UPDRS (55 items) and MDS-UPDRS (65 items) to 877 English speaking (78% non-Latino Caucasian) patients with Parkinson's disease from 39 sites."

Establishes UPDRS and its MDS-sponsored revision as the clinician-administered instruments used at scale to assess PD severity, rather than citing an incidental outcome measure from a single rehabilitation case report.

PMID:19025984 SUPPORT Human clinical

"The combined clinimetric results of this study support the validity of the MDS-UPDRS for rating PD."

Supports the clinimetric validity of the MDS-UPDRS revision, which correlated highly with the original UPDRS (rho = 0.96) bound here.

🪜

Stages

Stage 1: Unilateral Disease

Symptoms are present on one side of the body only. Mild unilateral involvement with minimal or no functional impairment. Patients may exhibit resting tremor, rigidity, or bradykinesia on one limb or side. Daily activities are not significantly affected.

Original Hoehn and Yahr staging scale from 1967 (PMID:6067254). A modified scale with 0.5 increments (Stages 1.5, 2.5) has been widely adopted but lacks formal clinimetric validation.

Show evidence (2 references)

PMID:27918765 SUPPORT

"the Hoehn and Yahr scale, with the lowest grade indicating unilateral involvement with minimal or no functional impairment"

This describes Stage 1 (the lowest grade) as unilateral involvement with minimal or no functional impairment.

PMID:34461264 SUPPORT Model organism

"Clinical findings indicate that LID typically only occurs following the progression of PD motor symptoms from the unilateral (Hoehn and Yahr (HY) Stage I) to the bilateral stage (HY Stage II)."

This identifies Stage I as the unilateral phase of PD motor symptoms.

Stage 2: Bilateral Disease Without Balance Impairment

Symptoms are present on both sides of the body or at the midline. Bilateral involvement without impairment of balance. Patients show bilateral tremor, rigidity, and bradykinesia but maintain normal postural reflexes and physical independence.

Show evidence (2 references)

PMID:34461264 SUPPORT Model organism

"Clinical findings indicate that LID typically only occurs following the progression of PD motor symptoms from the unilateral (Hoehn and Yahr (HY) Stage I) to the bilateral stage (HY Stage II)."

This identifies Stage II as the bilateral stage of PD motor symptom progression.

PMID:15372591 SUPPORT

"the scale fulfills at least some criteria for reliability and validity, especially for the midranges of the scale (Stages 2-4)."

The MDS Task Force report validates the reliability of midrange stages (2-4) of the Hoehn and Yahr scale.

Stage 3: Bilateral Disease With Postural Instability

Mild to moderate bilateral disease with early postural instability. The first sign of impaired righting reflexes appears. Patients remain physically independent in daily activities but have clinically evident balance impairment.

Show evidence (2 references)

PMID:20181069 SUPPORT

"The modified Hoehn and Yahr scale was 3: mild to moderate bilateral disease; some postural instability; physically independent."

This directly defines Stage 3 as mild to moderate bilateral disease with some postural instability while remaining physically independent.

PMID:15372591 SUPPORT

"Because the HY scale is weighted heavily toward postural instability as the primary index of disease severity, it does not capture completely impairments or disability from other motor features of PD and gives no information on nonmotor problems."

This highlights that the Hoehn and Yahr scale weights postural instability as a primary severity index, providing context for why balance impairment becomes central at Stage 3.

Stage 4: Severe Disability, Still Ambulatory

Fully developed, severely disabling disease. Patients remain ambulatory but have marked loss of independence in daily activities. More than half require assistance with most activities of daily living, despite retained ability to complete walk-based assessments.

Show evidence (2 references)

PMID:34125001 SUPPORT

"Her disease severity was classified as Hoehn and Yahr stage 4. The unified Parkinson's disease rating scale (UPDRS) part 3, 10-m walk test (10MWT), timed up-and-go test (TUG), Berg balance scale (BBS), and 30-s chair stand test (30-s CST) were used for assessment before and after intervention."

This stage 4 case report shows that advanced patients can remain ambulatory enough to perform walk-based assessments despite severe motor impairment.

PMID:40162911 SUPPORT

"In the H-Y Stage 4 group, more than half of the patients required assistance with most ADLs, except feeding and bowel control."

This directly supports substantial dependence in daily activities as a defining functional feature of Stage 4 disease.

Stage 5: Wheelchair-Bound or Bedridden

Patient is confined to wheelchair or bedridden unless aided. Complete dependence on caregivers for all activities. Represents the most severe stage of motor disability in Parkinson's disease.

Show evidence (1 reference)

PMID:27918765 SUPPORT

"the highest grade defining patients with complete confinement to wheelchair or bed."

This directly defines Stage 5 (the highest grade) as complete confinement to wheelchair or bed.

📊

Prevalence

Population aged 65 years and older (worldwide)

Point prevalence 2500.0 per 100,000 (2000.0–3000.0) >1 in 1,000

Parkinson disease affects 2-3% of the population aged 65 years and older, making it the second-most common neurodegenerative disorder. Prevalence rises steeply with age.

Show evidence (1 reference)

PMID:28332488 SUPPORT Human clinical

"Parkinson disease is the second-most common neurodegenerative disorder that affects 2-3% of the population ≥65 years of age."

This Nature Reviews Disease Primers review states that PD affects 2-3% of people aged 65 and older, supporting the point-prevalence estimate.

📊

Related Datasets

Large-scale metagenomics of Parkinson's disease gut microbiome bioproject:PRJNA834801

Shotgun metagenomics from the NeuroGenetics Research Consortium (NGRC) with over 30% of species, genes and pathways showing altered abundances in PD. Identified polymicrobial clusters and competitive relationships.

human gut metagenome WGS

fecal sample OBI:0002503

Conditions: Parkinson's disease healthy controls

PMID:36357667

Nature Communications 2022 - largest PD metagenomics to date

Show evidence (1 reference)

PMID:37449597 SUPPORT

"This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."

This supports the relevance of gut microbiome datasets to PD mechanisms.

Multi-omics analysis of PD gut microbiome gene expression bioproject:PRJNA782492

Integrated metagenomics and metatranscriptomics analyzing microbiome gene co-expression networks in Parkinson's disease. Observed significant depletion of hub genes in PD patients.

human gut metagenome WGS

fecal sample OBI:0002503

Conditions: Parkinson's disease healthy controls

npj Biofilms and Microbiomes 2025 - multi-omics approach

Show evidence (1 reference)

PMID:37449597 SUPPORT

"This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."

This supports the relevance of gut microbiome datasets to PD mechanisms.

Longitudinal gut microbiome in Parkinson's disease bioproject:PRJNA808166

Longitudinal study investigating gut microbiome changes in PD patients and impact of device-assisted therapies. Tracks microbiome alterations with disease progression.

human gut metagenome

fecal sample OBI:0002503

Conditions: Parkinson's disease baseline Parkinson's disease follow-up

Frontiers Aging Neuroscience 2022 - longitudinal design

Show evidence (1 reference)

PMID:37449597 SUPPORT

"This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."

This supports the relevance of gut microbiome datasets to PD mechanisms.

PD gut microbiome meta-analysis cohort bioproject:PRJNA530401

Metagenomic sequencing data from PD patients and controls contributing to cross-cohort meta-analyses. Identified alterations linked to intestinal inflammation including reduced butyrate producers.

human gut metagenome WGS

fecal sample OBI:0002503

Conditions: Parkinson's disease healthy controls

npj Parkinson's Disease 2021 - meta-analysis contributing cohort

Show evidence (1 reference)

PMID:37449597 SUPPORT

"This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."

This supports the relevance of gut microbiome datasets to PD mechanisms.

Metabolomics of sebum reveals lipid dysregulation in Parkinson's disease metabolights:MTBLS2266

LC-MS sebum metabolomics in Parkinson's disease, including drug-naive and medicated cohorts, compared with well-matched controls to identify lipid pathway alterations.

human METABOLOMICS n=274

Conditions: Parkinson's disease drug-naive Parkinson's disease medicated Parkinson's disease healthy controls

Findings

Sebum metabolomics in PD shows alterations in lipid metabolism pathways, including the carnitine shuttle, sphingolipid metabolism, arachidonic acid metabolism and fatty acid biosynthesis.

Show evidence (1 reference)

metabolights:MTBLS2266 SUPPORT

"Pathway enrichment analysis shows alterations in lipid metabolism related to the carnitine shuttle, sphingolipid metabolism, arachidonic acid metabolism and fatty acid biosynthesis."

The dataset description reports lipid pathway alterations detected in sebum metabolomics for PD.

LC-MS profiling of 274 participants detected metabolites predictive of PD phenotype.

Show evidence (1 reference)

metabolights:MTBLS2266 SUPPORT

"We used liquid chromatography-mass spectrometry (LC-MS) to analyse 274 samples from participants (80 drug naïve PD, 138 medicated PD and 56 well matched control subjects) and detected metabolites that could predict PD phenotype."

The dataset description specifies LC-MS profiling and the PD/control cohort sizes.

PMID:33707447

Metabolomics profiling of sebum as a non-invasive biofluid for PD.

Show evidence (1 reference)

metabolights:MTBLS2266 SUPPORT

"Here, we use a metabolomics profiling approach to identify changes to lipids in PD observed in sebum, a non-invasively available biofluid."

Establishes that the dataset focuses on PD sebum metabolomics.

Metabolomic Changes in Idiopathic and GBA1 Parkinson’s Disease metabolights:MTBLS10743

Mass spectrometry metabolomics comparing idiopathic Parkinson's disease and GBA1-associated Parkinson's disease cohorts with controls.

human METABOLOMICS

Conditions: idiopathic Parkinson's disease GBA1-associated Parkinson's disease healthy controls

Findings

Metabolomic signatures differ between GBA1-PD and idiopathic PD in sebum and serum with good specificity and sensitivity.

Show evidence (1 reference)

metabolights:MTBLS10743 SUPPORT

"Differences in metabolomic signatures were seen between ... GBA1-PD and iPD in sebum and serum with good specificity and sensitivity."

The dataset description reports discriminative metabolomic signatures between GBA1-PD and idiopathic PD.

Serum pathways implicated include sphingolipid metabolism, amino sugar metabolism and amino acid pathways, while sebum features are hypothesised to be lipid degradation products.

Show evidence (1 reference)

metabolights:MTBLS10743 SUPPORT

"Significant pathways in serum included sphingolipid metabolism, amino sugar metabolism and amino acid pathways, whereas significant features between groups in sebum are hypothesised to be lipid degradation products."

The dataset description lists pathway-level differences in serum and hypothesized lipid degradation products in sebum.

Preprint dataset describing metabolic changes in idiopathic vs GBA1 PD.

Show evidence (1 reference)

metabolights:MTBLS10743 SUPPORT

"Here, we use mass spectrometry based metabolomics to analyse serum and sebum samples from 50 genotyped participants and find differences in lipid and sugar regulation, oxidative stress and the production of amino acids and neurotransmitters which distinguish ... GBA1-PD from iPD."

Establishes the dataset's serum and sebum metabolomics design distinguishing GBA1-PD from idiopathic PD.

A multi-region single nucleus transcriptomic atlas of Parkinson's disease cellxgene:d5d0df8f-4eee-49d8-a221-a288f50a1590

Single-nucleus RNA-seq atlas of Parkinson's disease spanning multiple brain regions, providing cell-type-resolved transcriptomic profiles of dopaminergic neurons and glial populations in PD and healthy controls.

human SINGLE CELL RNA SEQ

brain tissue UBERON:0000955

Conditions: Parkinson's disease healthy controls

PMID:39317733

CZI CELLxGENE collection. DOI 10.1038/s41597-024-04117-y. Multi-region snRNA-seq atlas enabling virtual cell model training on PD-relevant cell states.

🧫

Experimental Models

Midbrain organoids with dopaminergic differentiation ORGANOID

Three-dimensional midbrain organoids reproduce aspects of human midbrain development. The review concludes they reliably reproduce mitochondrial and lysosomal dysfunction and, in SNCA triplication models, alpha-synuclein accumulation, but seldom progressive dopaminergic neurodegeneration or mature Lewy pathology.

Organism

Homo sapiens NCBITaxon:9606

Cell source

Human pluripotent stem cells differentiated toward midbrain fate

Culture

3D self-organizing midbrain organoid cultures

Publication

PMID:42727800

Pathograph links

Mitochondrial Dysfunction recapitulates fidelity: moderate observes: cellular Organoids reproduce mitochondrial dysfunction as reported in the reviewed organoid studies.

Limitations: Reported across organoid studies generally; the review does not tie this to a single genotype or cell population.

Show evidence (1 reference)

PMID:42727800 SUPPORT REVIEW SYNTHESIS In vitro / ex vivo

"Organoids reliably reproduce mitochondrial and lysosomal dysfunction"

The review synthesizes organoid studies as reproducing mitochondrial dysfunction, which supports treating midbrain organoids as informative for this node.

Autophagy-Lysosome Pathway Dysfunction recapitulates fidelity: moderate observes: cellular Organoids reproduce lysosomal dysfunction as reported in the reviewed organoid studies.

Limitations: Reported across organoid studies generally; the review does not tie this to a single genotype or cell population.

Show evidence (1 reference)

PMID:42727800 SUPPORT REVIEW SYNTHESIS In vitro / ex vivo

"Organoids reliably reproduce mitochondrial and lysosomal dysfunction"

The review synthesizes organoid studies as reproducing lysosomal dysfunction, which supports treating midbrain organoids as informative for this node.

Alpha-Synuclein Aggregation partially recapitulates fidelity: moderate observes: cellular Alpha-synuclein accumulation is reproduced in SNCA triplication organoid models.

Limitations: Accumulation is shown only in SNCA triplication models; the review reports that organoids rarely mature into Lewy pathology.

Divergences from the human mechanism

boundary omission qualifying

Organoid cultures last weeks to months and lack the decades of neuronal aging over which alpha-synuclein matures into Lewy bodies in patients, so the model captures early accumulation but rarely the mature inclusion stage of this node.

Show evidence (1 reference)

PMID:42727800 SUPPORT REVIEW SYNTHESIS In vitro / ex vivo

"in SNCA triplication models, α-synuclein accumulation"

The review reports alpha-synuclein accumulation in SNCA triplication organoid models, supporting the aggregation node only for that genetic setting.

Dopaminergic Neuron Loss partially recapitulates fidelity: low observes: cellular Organoids contain dopaminergic neurons, but the progressive, age-dependent course of their loss in patients is rarely reproduced.

Limitations: The review states organoids seldom show progressive neurodegeneration, so the progressive course of this node is rarely reproduced in the reported studies. The review does not state that dopaminergic neuron loss is absent from organoids.

Divergences from the human mechanism

boundary omission qualifying

The slow, decades-long progression of nigral dopaminergic neuron loss in patients falls outside an organoid culture's lifespan, so the model can show dopaminergic vulnerability but rarely the progressive degeneration this node describes.

Show evidence (1 reference)

PMID:42727800 SUPPORT REVIEW SYNTHESIS In vitro / ex vivo

"but seldom progressive neurodegeneration or mature Lewy pathology"

The review reports that organoids seldom reproduce progressive neurodegeneration, which supports treating them as only partially informative for this node: the progressive course of the loss is rarely captured.

🐁

Animal Models

Drosophila Dap160 heterozygous null with human alpha-synuclein expression

A genetic-interaction model for ITSN1 haploinsufficiency. Halving the fly ortholog Dap160 worsens alpha-synuclein-induced photoreceptor degeneration and age-dependent motor decline, while Dap160 overexpression lessens the eye degeneration. Dap160 heterozygotes without alpha-synuclein have no eye or motor phenotype.

Species

Drosophila melanogaster

Genotype

Heterozygous amorphic Dap160 (ITSN1 ortholog) allele with pan-neuronal (elav-GAL4) or eye-specific (GMR-GAL4) expression of human wild-type alpha-synuclein (UAS-SNCA)

Publication

PMID:40056900

Pathograph links

Dopaminergic Neuron Loss perturbs fidelity: low observes: organism Reduced Dap160 dosage enhances the neurodegeneration and motor decline caused by overexpressed human alpha-synuclein.

Limitations: Alpha-synuclein is overexpressed from a transgene rather than present at endogenous levels, the degeneration readout is in photoreceptors rather than dopaminergic neurons, and the motor assay uses pan-neuronal expression, so neither readout measures dopaminergic neuron loss directly.

Readouts

Alpha-synuclein-induced rough-eye degeneration

Direction: INCREASED

Interpretation: Larger disorganized eye area in Dap160 heterozygotes expressing alpha-synuclein than in alpha-synuclein flies alone.

Show evidence (1 reference)

PMID:40056900 SUPPORT Model organism

"Flies carrying a heterozygous null variant in Dap160 (the Drosophila ortholog of ITSN1)31 had exacerbated α-synuclein-induced degeneration, with more severe disorganization covering a larger eye area"

Reports the eye-degeneration measurement and its direction.

Climbing speed in alpha-synuclein-expressing flies

Direction: DECREASED

Interpretation: Dap160 heterozygosity worsens the age-dependent loss of climbing speed and increase in stumbling caused by neuronal alpha-synuclein.

Show evidence (1 reference)

PMID:40056900 SUPPORT Model organism

"Heterozygous loss of Dap160 worsened the phenotypes of α-synuclein-expressing flies across all ages"

Reports the locomotor readout across ages.

Alpha-Synuclein Aggregation measures fidelity: low observes: cellular Dap160 colocalizes with alpha-synuclein aggregates at synaptic boutons.

Limitations: Aggregate burden itself was not quantified across Dap160 genotypes, so the model places the ITSN1 ortholog at aggregates but does not show that ITSN1 dosage changes aggregation.

Show evidence (1 reference)

PMID:40056900 SUPPORT Model organism

"Dap160 co-localized with α-synuclein aggregates in 42.9% of 245 analyzed synaptic boutons"

Places the ITSN1 ortholog at alpha-synuclein aggregates in fly synapses, supporting the link to this node.

🧮

Computational Models

Alpha-Synuclein Aggregation BST Model KINETIC

Biochemical Systems Theory (BST) model of alpha-synuclein aggregation kinetics in dopaminergic neurons. Integrates dopamine metabolism, ubiquitin-proteasome system, and lysosomal degradation pathways. Simulates effects of oxidative stress and proteasome inhibition on synuclein accumulation.

Repository ↗ PMID:19136028

Pathograph links

Alpha-Synuclein Aggregation Models alpha-synuclein aggregation kinetics and degradation-pathway effects in dopaminergic neurons.

First comprehensive kinetic model of PD-related protein aggregation

Whole Dopaminergic Neuron SBML Model SBML KINETIC

Large-scale Systems Biology Markup Language (SBML) model of dopaminergic neuron containing 139 reactions and 111 metabolites. Captures dopamine synthesis, vesicular storage, release, reuptake, and degradation alongside mitochondrial function and oxidative stress.

Repository ↗ PMID:24196439

Pathograph links

Striatal Dopamine Deficiency Models dopamine synthesis, storage, release, reuptake, and degradation in dopaminergic-neuron physiology.

Mitochondrial Dysfunction Models mitochondrial metabolism alongside dopamine handling in dopaminergic neurons.

Enables simulation of drug effects on dopaminergic neurotransmission

Basal Ganglia Spiking Neural Network PHYSIOLOGICAL

Computational model of the basal ganglia circuit capturing dopamine-modulated dynamics between striatum, globus pallidus, subthalamic nucleus, and substantia nigra. Simulates pathological beta-band oscillations and motor dysfunction in PD.

PMID:29666208

Pathograph links

Basal Ganglia Circuit Dysfunction Models dopamine-modulated basal ganglia circuit dynamics, beta-band oscillations, and DBS effects.

Models circuit-level effects of dopamine depletion and DBS therapy

Alpha-Synuclein Prion-like Spreading Model AGENT_BASED

Network diffusion model simulating prion-like propagation of misfolded alpha-synuclein through brain connectome. Uses graph-theoretical approach to predict spatial patterns of neurodegeneration from initial seeding sites.

Pathograph links

Alpha-Synuclein Aggregation Models connectome-based propagation of misfolded alpha-synuclein pathology.

Predicts Braak staging patterns from connectivity-based spreading

PD Map Cohort-Specific Probabilistic Boolean Models SBML-qual CaSQ, pyMaBoSS, CellDesigner BOOLEAN_NETWORK

Probabilistic Boolean Networks (PBNs) built from the Parkinson's disease map, the largest curated repository of PD pathway diagrams. Pathways enriched in the Parkinson's Progression Markers Initiative (PPMI) cohort were exported from the PD map in CellDesigner SBML format, translated to SBML-qual with CaSQ, and parameterised against cohort miRNA and transcriptomic data so that each model represents a specific PD subgroup (prodromal, SWEDD, parkinsonism). Simulating the resulting models with pyMaBoSS reveals subtype-specific differences in dopamine transcription, PI3K/AKT signalling, FOXO3 activity, mTOR-MAPK signalling and PRKN mitophagy. The probabilistic parameterisation, rather than plain Boolean logic, is what lets cohort-level data enter the model.

Repository ↗ PMID:39429779

Pathograph links

Autophagy-Lysosome Pathway Dysfunction recapitulates fidelity: moderate observes: molecular PRKN mitophagy is one of the enriched PD map pathways converted into a cohort-parameterised Boolean model, and autophagy/mitophagy activity is one of the axes on which the subtypes separate.

Limitations: The model is parameterised from cohort-level miRNA and transcriptomic data rather than from direct measurement of autophagic flux, so it represents transcriptional regulation of the pathway rather than the degradative process itself.

Divergences from the human mechanism

proxy quantity qualifying

The model represents transcriptional regulation of the autophagy-lysosome pathway. The node describes the degradative process itself -- flux through that pathway -- which transcript abundance constrains but does not measure.

calibration provenance qualifying

Node transition probabilities were fitted to cohort-level miRNA and transcriptomic data, not to any direct assay of autophagic flux.

scale extrapolation qualifying

A molecular signalling network standing for a cell-scale degradative process.

Readouts

PRKN-mitophagy model activity across PD subgroups

Direction: ALTERED

Interpretation: Mitophagy and autophagy activities differ between the SWEDD, prodromal and parkinsonism subgroups rather than moving in one direction across all of PD.

Show evidence (1 reference)

PMID:39429779 SUPPORT Computational

"differences in autophagy and mitophagy activities were observed, suggesting unique disease mechanisms within each PD subtype"

Reports the subtype-dependent autophagy/mitophagy readout this link records.

Show evidence (1 reference)

PMID:39429779 SUPPORT Computational

"The enriched pathways included dopamine transcription pathways, PI3k/AKT signaling, FOXO3 activity, mTOR-MAPK signaling, and PRKN mitophagy"

Names PRKN mitophagy among the pathways modelled, linking this model to the autophagy-lysosome node.

Striatal Dopamine Deficiency partially recapitulates fidelity: low observes: molecular Dopamine transcription pathways are among the enriched PD map diagrams converted to Boolean models and show distinct behaviour across subtypes.

Limitations: The model represents transcriptional regulation of dopamine synthesis in a cohort-parameterised signalling network; it does not represent striatal dopamine concentration, nigrostriatal terminal loss, or the presynaptic deficit that defines this node clinically.

Divergences from the human mechanism

proxy quantity invalidating

The model's quantity is transcriptional regulation of dopamine-synthesis genes. The node's quantity is dopamine concentration in the striatum. These are different measurements separated by transcription, translation, synthesis, transport and terminal survival, and the model cannot be read as reporting the second. This is the divergence behind the link's LOW fidelity, and it is invisible to the scale comparison alone.

boundary omission qualifying

Nigrostriatal terminal loss and the presynaptic deficit that clinically defines this node are not in the model.

scale extrapolation qualifying

Two scale steps: a molecular network inferring the dopaminergic tone of an anatomical structure.

calibration provenance qualifying

Parameterised from cohort-level omics rather than from striatal dopamine measurement in the cohorts the model stratifies.

Show evidence (1 reference)

PMID:39429779 SUPPORT INDIRECT Computational

"These models revealed distinct behaviors in key molecular pathways across PD subtypes, including dopamine transcription, PI3K/AKT signaling, FOXO3 activity, mTOR-MAPK signaling, and PRKN mitophagy"

Supports a transcription-level dopamine claim. Indirect: the quote asserts subtype-specific behaviour of dopamine-transcription pathways, and striatal dopamine deficiency follows only by an inference step across transcription, synthesis and terminal survival -- which is also why fidelity here is LOW.

Findings

Cohort-level and real-world patient data were integrated into the logical models to represent subtype-specific pathway deregulation.

Show evidence (1 reference)

PMID:39429779 SUPPORT Computational

"By integrating cohort-level and real-world patient data, we modeled PD's subtype-specific pathway deregulations, providing a refined representation of its molecular landscape"

States the data-integration step that makes these models cohort-specific.

Curated as part of the Boolean/logical modelling track; see docs/superpowers/plans/2026-08-28-boolean-modeling-and-pathographs.md. Literature-referenced, not runnable in-repo: dismech-perturb has no SBML-qual execution path yet. Note this is a *probabilistic* Boolean network — cohort data enter as node transition probabilities, so it is not a plain deterministic Boolean model.

Show evidence (2 references)

PMID:39429779 SUPPORT Computational

"we employed systems medicine approaches using the PD map, a detailed repository of PD-related interactions and applied Probabilistic Boolean Networks (PBNs) to capture the stochastic nature of molecular dynamics"

Establishes the PD map as the knowledge source and PBNs as the modelling formalism for this entry.

PMID:39429779 SUPPORT Computational

"The pathways identified via the enrichment analysis were exported from the PD map in CellDesigner SBML format and translated into SBML-qual files by the CaSQ tool"

Documents the CaSQ map-to-model translation and the SBML-qual format recorded in model_format.

{ }

Source YAML

click to show

name: Parkinson's Disease
creation_date: '2025-12-18T17:01:35Z'
description: >-
  Parkinson's disease is a progressive neurodegenerative movement disorder caused
  by the loss of dopaminergic neurons in the substantia nigra pars compacta,
  producing striatal dopamine deficiency and basal ganglia circuit dysfunction.
  It manifests as bradykinesia, resting tremor, rigidity, and postural instability,
  with non-motor features. The pathological hallmark is intraneuronal aggregation
  of misfolded alpha-synuclein (Lewy bodies), with mitochondrial dysfunction and
  oxidative stress contributing to neurodegeneration.
category: Complex
parents:
- Neurodegenerative Disease
- Movement Disorder
disease_term:
  preferred_term: Parkinson disease
  term:
    id: MONDO:0005180
    label: Parkinson disease
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0008199
      label: late-onset Parkinson disease
    mapping_predicate: skos:narrowMatch
    mapping_source: manual curation
    mapping_justification: >
      MONDO:0008199 (late-onset Parkinson disease, OMIM:168600, "PARK"/"LOPD";
      onset after ~age 50) is the common sporadic/idiopathic adult-onset form and
      a child of MONDO:0005180. This entry curates Parkinson disease at the broad
      MONDO:0005180 level, and its pathophysiology (α-synucleinopathy and
      dopaminergic neurodegeneration, SNCA/LRRK2/GBA1) substantively covers the
      late-onset form. Recorded as a narrowMatch so coverage tooling resolves
      MONDO:0008199 to this entry rather than flagging it as uncurated.
has_subtypes:
- name: PARK1
  display_name: SNCA-associated Parkinson disease (PARK1)
  description: >-
    Autosomal-dominant Parkinson disease caused by a mutation in SNCA. The
    mutation was identified in a large Italian kindred and in three unrelated
    families of Greek origin with autosomal dominant inheritance, and was the
    finding that established alpha-synuclein as a Mendelian cause of the
    disease. MONDO's separate PARK4 term covers the SNCA locus multiplications;
    see that row for the distinction.
  subtype_term:
    preferred_term: autosomal dominant Parkinson disease 1
    term:
      id: MONDO:0008200
      label: autosomal dominant Parkinson disease 1
  genes:
  - preferred_term: SNCA
    term:
      id: hgnc:11138
      label: SNCA
  evidence:
  - reference: PMID:9197268
    reference_title: "Mutation in the alpha-synuclein gene identified in families with Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A mutation was identified in the alpha-synuclein gene, which codes for a presynaptic protein thought to be involved in neuronal plasticity, in the Italian kindred and in three unrelated families of Greek origin with autosomal dominant inheritance for the PD phenotype."
    explanation: Establishes SNCA point mutation as a dominant Mendelian cause of Parkinson disease, the entity MONDO labels PARK1.
- name: PARK4
  display_name: SNCA multiplication Parkinson disease (PARK4)
  description: >-
    Autosomal-dominant Parkinson disease caused by duplication or triplication of
    the SNCA locus rather than by a coding change, so the mechanism is increased
    wild-type alpha-synuclein gene dosage. Clinical severity tracks copy number.
    HGNC records PARK1 and PARK4 as previous symbols of SNCA, so the two MONDO
    terms are one gene distinguished by allelic mechanism, not two loci.
  subtype_term:
    preferred_term: autosomal dominant Parkinson disease 4
    term:
      id: MONDO:0011562
      label: autosomal dominant Parkinson disease 4
  genes:
  - preferred_term: SNCA
    term:
      id: hgnc:11138
      label: SNCA
  evidence:
  - reference: PMID:18571778
    reference_title: Genomic investigation of alpha-synuclein multiplication and parkinsonism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SNCA dosage is responsible for parkinsonism, autonomic dysfunction, and dementia observed within each family."
    explanation: Attributes the phenotype in five multiplication families to SNCA copy number, which is the defining mechanism of this subtype.
  - reference: PMID:18571778
    reference_title: Genomic investigation of alpha-synuclein multiplication and parkinsonism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The severity of clinical presentation is correlated with SNCA dosage and does not appear to be overtly affected by the presence of other genes in the multiplicated region."
    explanation: Supports the dose-severity relationship and excludes neighbouring genes in the duplicated interval as the driver.
- name: PARK6
  display_name: PINK1 early-onset Parkinson disease (PARK6)
  description: >-
    Autosomal-recessive early-onset Parkinson disease caused by biallelic PINK1
    variants affecting the kinase domain. PINK1 is mitochondrially located, and
    its loss links the subtype to the mitochondrial quality-control arm of the
    pathograph.
  subtype_term:
    preferred_term: autosomal recessive early-onset Parkinson disease 6
    term:
      id: MONDO:0011613
      label: autosomal recessive early-onset Parkinson disease 6
  genes:
  - preferred_term: PINK1
    term:
      id: hgnc:14581
      label: PINK1
  evidence:
  - reference: PMID:15087508
    reference_title: "Hereditary early-onset Parkinson's disease caused by mutations in PINK1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we show that mutations in PINK1 (PTEN-induced kinase 1) are associated with PARK6."
    explanation: Identifies PINK1 as the gene at the PARK6 locus, which is the MONDO term bound here.
  - reference: PMID:15087508
    reference_title: "Hereditary early-onset Parkinson's disease caused by mutations in PINK1."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Cell culture studies suggest that PINK1 is mitochondrially located and may exert a protective effect on the cell that is abrogated by the mutations, resulting in increased susceptibility to cellular stress."
    explanation: Supports the mitochondrial localization and loss-of-protection mechanism that places this subtype on the mitochondrial dysfunction node.
- name: PARK15
  display_name: FBXO7 parkinsonian-pyramidal syndrome (PARK15)
  description: >-
    Autosomal-recessive early-onset parkinsonism combined with pyramidal tract
    signs, caused by biallelic FBXO7 variants. Its defining feature is that
    combination of early-onset progressive parkinsonism with pyramidal tract
    involvement, which is the phenotype the discovery study delineated as
    PARK15.
  subtype_term:
    preferred_term: parkinsonian-pyramidal syndrome
    term:
      id: MONDO:0009830
      label: parkinsonian-pyramidal syndrome
  genes:
  - preferred_term: FBXO7
    term:
      id: hgnc:13586
      label: FBXO7
  evidence:
  - reference: PMID:19038853
    reference_title: "FBXO7 mutations cause autosomal recessive, early-onset parkinsonian-pyramidal syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclusively show that recessive FBXO7 mutations cause progressive neurodegeneration with extrapyramidal and pyramidal system involvement, delineating a novel genetically defined entity that we propose to designate as PARK15."
    explanation: Establishes FBXO7 as the cause of the parkinsonian-pyramidal entity MONDO binds here, and names it PARK15.
  - reference: PMID:19038853
    reference_title: "FBXO7 mutations cause autosomal recessive, early-onset parkinsonian-pyramidal syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An FBXO7 homozygous truncating mutation (Arg498Stop) was found in an Italian family, while compound heterozygous mutations (a splice-site IVS7 + 1G/T mutation and a missense Thr22Met mutation) were present in a Dutch family."
    explanation: Documents the biallelic FBXO7 genotypes in the two families, supporting recessive inheritance for this subtype.
- name: PARK17
  display_name: VPS35 late-onset Parkinson disease (PARK17)
  description: >-
    Autosomal-dominant late-onset Parkinson disease caused by the recurrent
    VPS35 p.Asp620Asn variant. VPS35 is a component of the retromer complex.
    Penetrance is high but incomplete, and mean age of onset in the affected
    individuals of the discovery families was 53 years.
  subtype_term:
    preferred_term: Parkinson disease 17
    term:
      id: MONDO:0013625
      label: Parkinson disease 17
  genes:
  - preferred_term: VPS35
    term:
      id: hgnc:13487
      label: VPS35
  evidence:
  - reference: PMID:21763483
    reference_title: "A mutation in VPS35, encoding a subunit of the retromer complex, causes late-onset Parkinson disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found a missense mutation, c.1858G>A (p.Asp620Asn), in the VPS35 gene in all seven affected family members who are alive."
    explanation: Identifies the recurrent VPS35 variant that defines this subtype.
  - reference: PMID:21763483
    reference_title: "A mutation in VPS35, encoding a subunit of the retromer complex, causes late-onset Parkinson disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "By screening additional PD cases, we saw the same variant cosegregating with the disease in an autosomal-dominant mode with high but incomplete penetrance in two further families with five and ten affected members, respectively."
    explanation: Supports autosomal-dominant transmission with reduced penetrance in two replication families.
  - reference: PMID:21763483
    reference_title: "A mutation in VPS35, encoding a subunit of the retromer complex, causes late-onset Parkinson disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean age of onset in the affected individuals was 53 years."
    explanation: Source for the age of onset stated in this subtype description.
- name: PARK19A
  display_name: DNAJC6 juvenile parkinsonism (PARK19A)
  description: >-
    Autosomal-recessive juvenile parkinsonism caused by a DNAJC6 variant
    identified by homozygosity mapping. DNAJC6 encodes auxilin, the
    neuron-specific clathrin-uncoating co-chaperone, so the subtype sits on the
    synaptic-vesicle recycling arm of the pathograph rather than the
    mitochondrial one. Parkinsonism is usually not the presenting feature:
    developmental delay, intellectual disability, seizures, other movement
    disorders and neuropsychiatric features occur in the majority of
    juvenile-onset individuals and often precede it. In the two siblings of the
    PMID:42414182 case series, levodopa gave only mild benefit and dose escalation
    provoked an adverse motor reaction.
  subtype_term:
    preferred_term: juvenile onset Parkinson disease 19A
    term:
      id: MONDO:0014231
      label: juvenile onset Parkinson disease 19A
  genes:
  - preferred_term: DNAJC6
    term:
      id: hgnc:15469
      label: DNAJC6
  evidence:
  - reference: PMID:42414182
    reference_title: "Novel Homozygous Pathogenic Variant in DNAJC6 Causes Rapid Progressive Parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Both patients exhibited developmental regression, parkinsonism with dystonia, cognitive decline, dysphagia, and marked sialorrhea, with severe, accelerated functional deterioration."
    explanation: Describes the juvenile phenotype in the two siblings (aged 17 and 14), including developmental regression and rapid functional decline.
  - reference: PMID:42414182
    reference_title: "Novel Homozygous Pathogenic Variant in DNAJC6 Causes Rapid Progressive Parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Levodopa produced only mild benefit; in the older sibling, dose escalation provoked an adverse reaction with sustained upgaze/ophthalmoparesis, opisthotonus, and hypertension."
    explanation: Reports poor levodopa response and a dose-related adverse reaction in the older sibling; the treatment-response sentence in this subtype's description rests on it.
  - reference: PMID:22563501
    reference_title: "A deleterious mutation in DNAJC6 encoding the neuronal-specific clathrin-uncoating co-chaperone auxilin, is associated with juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Using homozygosity mapping and whole exome sequencing we identified a deleterious mutation in DNAJC6 in two patients with juvenile parkinsonism."
    explanation: Identifies DNAJC6 in juvenile parkinsonism, the phenotype MONDO files as PARK19A.
  - reference: PMID:22563501
    reference_title: "A deleterious mutation in DNAJC6 encoding the neuronal-specific clathrin-uncoating co-chaperone auxilin, is associated with juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mutation was associated with abnormal transcripts and marked reduced DNAJC6 mRNA level."
    explanation: Supports a loss-of-expression consequence for the reported DNAJC6 allele.
  - reference: PMID:33983693
    reference_title: "DNAJC6 Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "Developmental delay, intellectual disability, seizures, other movement disorders (e.g., dystonia, spasticity, myoclonus), and neuropsychiatric features occur in the majority of individuals with juvenile onset and often precede parkinsonism."
    explanation: >-
      The GeneReviews chapter's account of the extra-parkinsonian features that
      distinguish the juvenile form, and of the fact that they usually come first.
      Graded REVIEW_SYNTHESIS because the chapter synthesises the reported cases
      rather than reporting its own.
- name: PARK19B
  display_name: DNAJC6 early-onset Parkinson disease (PARK19B)
  description: >-
    Autosomal-recessive early-onset Parkinson disease caused by homozygous
    DNAJC6 variants, with onset in the third to fifth decade and slow
    progression. It
    is the milder end of the DNAJC6 spectrum and is separated from PARK19A by
    onset and course rather than by gene.
  subtype_term:
    preferred_term: Parkinson disease 19B, early-onset
    term:
      id: MONDO:0800369
      label: Parkinson disease 19B, early-onset
  genes:
  - preferred_term: DNAJC6
    term:
      id: hgnc:15469
      label: DNAJC6
  evidence:
  - reference: PMID:26528954
    reference_title: "DNAJC6 Mutations Associated With Early-Onset Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified two families with different novel homozygous DNAJC6 mutations segregating with PD."
    explanation: Reports biallelic DNAJC6 variants segregating in two early-onset PD families.
  - reference: PMID:33983693
    reference_title: "DNAJC6 Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "A minority of individuals with DNAJC6 Parkinson disease develop early-onset parkinsonism with symptom onset in the third to fourth decade and absence of additional neurologic features."
    explanation: >-
      The basis for separating this row from PARK19A: a minority present with
      parkinsonism alone and later onset. The chapter gives the window as the third
      to fourth decade where PMID:26528954 reports third to fifth; both are kept
      rather than reconciled, since they are different case series.
  - reference: PMID:26528954
    reference_title: "DNAJC6 Mutations Associated With Early-Onset Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All these cases fulfilled the criteria for a clinical diagnosis of early-onset PD, had symptoms onset in the third-to-fifth decade, and slow disease progression."
    explanation: Source for the onset window and slow course that distinguish this subtype from the juvenile DNAJC6 form.
- name: PARK20
  display_name: SYNJ1 early-onset parkinsonism (PARK20)
  description: >-
    Autosomal-recessive early-onset parkinsonism with dystonia and cognitive
    deterioration, caused by biallelic SYNJ1 variants. Synaptojanin 1 is a
    phosphoinositide phosphatase required for postendocytic synaptic-vesicle
    recycling, placing this subtype alongside the DNAJC6 forms. Levodopa
    response was poor in the index family.
  subtype_term:
    preferred_term: early-onset Parkinson disease 20
    term:
      id: MONDO:0014233
      label: early-onset Parkinson disease 20
  genes:
  - preferred_term: SYNJ1
    term:
      id: hgnc:11503
      label: SYNJ1
  evidence:
  - reference: PMID:23804577
    reference_title: "Mutation in the SYNJ1 gene associated with autosomal recessive, early-onset Parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we report the identification, by homozygosity mapping and exome sequencing, of a SYNJ1 homozygous mutation (p.Arg258Gln) segregating with disease in an Italian consanguineous family with Parkinsonism, dystonia, and cognitive deterioration."
    explanation: Identifies the biallelic SYNJ1 variant and the phenotype that defines this subtype.
  - reference: PMID:23804577
    reference_title: "Mutation in the SYNJ1 gene associated with autosomal recessive, early-onset Parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Response to levodopa was poor, and limited by side effects."
    explanation: Source for the poor levodopa response stated in this subtype description.
- name: PARK22
  display_name: CHCHD2 late-onset Parkinson disease (PARK22)
  description: >-
    Late-onset Parkinson disease segregating as an autosomal-dominant trait in
    Japanese families with CHCHD2 variants. The evidence is weaker than for the
    other dominant loci curated here: the discovery study found three variants
    in four of 341 autosomal-dominant index cases and stated that its own
    finding needed confirmation in other populations, and the ClinGen
    Gene-Disease Validity table lists no CHCHD2-Parkinson disease assertion
    (checked 2026-09-25).
  subtype_term:
    preferred_term: Parkinson disease 22, autosomal dominant
    term:
      id: MONDO:0014742
      label: Parkinson disease 22, autosomal dominant
  genes:
  - preferred_term: CHCHD2
    term:
      id: hgnc:21645
      label: CHCHD2
  evidence:
  - reference: PMID:25662902
    reference_title: "CHCHD2 mutations in autosomal dominant late-onset Parkinson's disease: a genome-wide linkage and sequencing study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three CHCHD2 mutations in four of 341 index cases from independent families with autosomal dominant Parkinson's disease were detected by CHCHD2 mutation screening"
    explanation: Gives the yield behind the CHCHD2-PD claim in the discovery cohort.
  - reference: PMID:25662902
    reference_title: "CHCHD2 mutations in autosomal dominant late-onset Parkinson's disease: a genome-wide linkage and sequencing study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CHCHD2 mutations are associated with, and might be a cause of, autosomal dominant Parkinson's disease."
    explanation: The authors' own hedged conclusion, quoted to keep this subtype's confidence level explicit rather than asserting an established Mendelian locus.
- name: PARK23
  display_name: VPS13C early-onset Parkinson disease (PARK23)
  description: >-
    Autosomal-recessive early-onset parkinsonism caused by biallelic truncating
    VPS13C variants, with rapid severe progression and early cognitive decline.
    VPS13C loss lowers mitochondrial membrane potential and increases
    PINK1/parkin-dependent mitophagy, which is why this subtype is wired to the
    mitochondrial dysfunction node.
  subtype_term:
    preferred_term: autosomal recessive early-onset Parkinson disease 23
    term:
      id: MONDO:0014796
      label: autosomal recessive early-onset Parkinson disease 23
  genes:
  - preferred_term: VPS13C
    term:
      id: hgnc:23594
      label: VPS13C
  evidence:
  - reference: PMID:26942284
    reference_title: Loss of VPS13C Function in Autosomal-Recessive Parkinsonism Causes Mitochondrial Dysfunction and Increases PINK1/Parkin-Dependent Mitophagy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This work suggests that loss of function of VPS13C is a cause of autosomal-recessive early-onset parkinsonism with a distinctive phenotype of rapid and severe progression."
    explanation: Establishes biallelic VPS13C loss of function as a cause of recessive early-onset parkinsonism.
  - reference: PMID:26942284
    reference_title: Loss of VPS13C Function in Autosomal-Recessive Parkinsonism Causes Mitochondrial Dysfunction and Increases PINK1/Parkin-Dependent Mitophagy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "VPS13C mutations are associated with a distinct form of early-onset parkinsonism characterized by rapid and severe disease progression and early cognitive decline"
    explanation: Source for the rapid progression and early cognitive decline stated in this subtype description.
- name: PARK25
  display_name: PTPA early-onset parkinsonism with intellectual disability (PARK25)
  description: >-
    Autosomal-recessive early-onset parkinsonism accompanied by intellectual
    disability, caused by biallelic missense PTPA variants that impair
    activation of the PP2A phosphatase. Motor symptoms in the reported families
    responded to levodopa and to subthalamic deep brain stimulation.
  subtype_term:
    preferred_term: Parkinson disease 25, autosomal recessive early-onset, with impaired intellectual development
    term:
      id: MONDO:0957576
      label: Parkinson disease 25, autosomal recessive early-onset, with impaired intellectual development
  genes:
  - preferred_term: PTPA
    term:
      id: hgnc:9308
      label: PTPA
  evidence:
  - reference: PMID:36073231
    reference_title: PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability."
    explanation: Establishes the gene, inheritance mode and combined motor plus cognitive phenotype that define this subtype.
  - reference: PMID:36073231
    reference_title: PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The affected subjects display juvenile-onset parkinsonism and intellectual disability."
    explanation: Describes the phenotype in the two discovery families.
  - reference: PMID:37046398
    reference_title: "Cross-Ethnic Variant Screening and Burden Analysis of PTPA in Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One patient with early-onset PD from a consanguineous family carried the homozygous variant p.Met329Val, while her parents and elder sister with heterozygous p.Met329Val were healthy."
    explanation: Independent replication in a third consanguineous family, with unaffected heterozygous relatives supporting recessive inheritance.
gene_sets:
- gene_set: MYGENESET:KEGG_PARKINSONS_DISEASE
  relationship: CANONICAL_PATHWAY
  note: >-
    KEGG Parkinson disease pathway.
- gene_set: MYGENESET:WP_PARKINSONS_DISEASE_PATHWAY
  relationship: CANONICAL_PATHWAY
  note: >-
    WikiPathways Parkinson disease pathway.
mechanistic_hypotheses:
- hypothesis_group_id: canonical_synucleinopathy_dopaminergic_neurodegeneration_model
  hypothesis_label: Canonical α-Synucleinopathy and Dopaminergic Neurodegeneration Model
  status: CANONICAL
  description: >-
    Misfolded α-synuclein aggregates into oligomers and Lewy bodies, propagates trans-synaptically in a prion-like manner, and induces progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta. The resulting striatal dopamine deficiency causes the cardinal motor signs (bradykinesia, rigidity, tremor, postural instability), while broader Lewy pathology in autonomic, brainstem, and cortical regions accounts for the non-motor symptoms (REM-sleep behavior disorder, hyposmia, constipation, cognitive impairment). Pathway evidence implicates impaired autophagy/lysosomal clearance (GBA), mitochondrial dysfunction (PINK1/Parkin), and oxidative stress as upstream amplifiers; loss of dopaminergic feedback to the indirect/direct basal ganglia circuits explains the motor circuit signature.
  notes: >-
    Retained as CANONICAL. The 2026 falcon
    hypothesis-search report
    (kb/hypotheses/Parkinsons_Disease/canonical_synucleinopathy_dopaminergic_neurodegeneration_model;
    openscientist timed out) confirms misfolded α-synuclein
    aggregation, Lewy-body formation, and progressive substantia-nigra
    pars-compacta dopaminergic neuron loss as the central
    mechanism. Three qualifications: (1) the prion-like cell-to-cell
    propagation model is well-validated in mouse and primate
    models (intracerebral PFF injection seeds endogenous
    aggregates and produces motor deficits), but its rate-limiting
    role in human sporadic PD remains debated; (2) GBA1
    heterozygosity, mitochondrial dysfunction (PINK1/Parkin),
    impaired autophagy/lysosomal clearance, and gut-brain axis
    (vagal Lewy pathology, microbiome) are increasingly
    recognized upstream amplifiers — particularly the gut-first
    Braak hypothesis, supported by hyposmia and REM-sleep
    behavior disorder preceding motor symptoms by 10-20 years;
    (3) LRRK2 G2019S and other genetic PD subtypes display Lewy-pathology
    variability, indicating molecular heterogeneity
    within the unified clinical syndrome. Anti-α-synuclein
    immunotherapies (prasinezumab, cinpanemab) have shown
    target engagement but limited clinical efficacy, suggesting
    aggregation may be a downstream marker rather than the
    rate-limiting therapeutic target.
  evidence:
  - reference: PMID:37048085
    reference_title: "Microglia Mediated Neuroinflammation in Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dopaminergic neuronal loss in substantia nigra pars compacta of the brain and aggregation of intracellular protein α-synuclein are the pathological characterizations"
    explanation: >
      Canonical mechanism review used as the seed reference for the
      hypothesis-search deep-research run.
- hypothesis_group_id: body_first_enteric_alpha_synuclein_model
  hypothesis_label: Body-First Enteric α-Synuclein Initiation Model
  status: ALTERNATIVE
  description: >-
    Alpha-synuclein pathology initiates in the enteric nervous system or other
    peripheral autonomic sites, then propagates through vagal connections to
    the dorsal motor nucleus and broader brainstem before joining the central
    alpha-synuclein propagation and dopaminergic-neurodegeneration cascade.
    This model best explains Parkinson disease presentations with early
    constipation, REM-sleep behavior disorder, autonomic dysfunction, and
    early peripheral/cardiac sympathetic denervation.
  notes: >-
    Evidence is strongest for the gut-to-brain propagation route in animal
    models where truncal vagotomy or alpha-synuclein deficiency blocks spread.
    Human clinical and imaging studies support a body-first subtype pattern,
    but microbiome dysbiosis and enteric seeding remain unresolved as causal
    triggers versus modifiers or consequences. The consequence reading now has a
    curated counterpart: Striatal Dopamine Deficiency carries a downstream edge
    to Gut Microbiome Dysbiosis, sourced to a rat nigrostriatal lesion that
    shifts gram-negative bacterial classes and lowers short-chain fatty acids.
    That edge is deliberately not tagged to this hypothesis group, because it
    describes a consequence of established dopaminergic loss rather than the
    origin site of alpha-synuclein pathology.

    The 2026 OpenScientist hypothesis-search report
    (kb/hypotheses/Parkinsons_Disease/body_first_enteric_alpha_synuclein_model)
    judges this model PARTIALLY SUPPORTED and recommends retaining ALTERNATIVE
    status: it is one well-supported origin-site pathway (an estimated ~20-30%
    of PD) within the multi-origin Synuclein Origin and Connectome (SOC)
    framework, not a universal disease mechanism. Convergent support spans
    mouse gut-to-brain transmission (vagotomy and α-syn knockout each block
    spread), human truncal-vagotomy epidemiology (reduced PD risk at long
    follow-up), gut-microbiota dependence in α-syn-overexpressing mice, and a
    distinct body-first clinical-imaging signature (more symmetric nigrostriatal
    degeneration, early cardiac sympathetic denervation). Key qualifications:
    (1) the upstream trigger for enteric α-syn misfolding is unknown; (2)
    enteric α-syn immunohistochemistry lacks diagnostic specificity (positive
    also in controls); (3) LRRK2-associated PD is frequently α-syn seed
    amplification assay (SAA)-negative, showing α-syn-independent parkinsonian
    pathways; (4) 6-43% of cases deviate from caudo-rostral Braak staging, iRBD
    prodrome is heterogeneous, FMT trials are inconsistent, and anti-α-syn
    immunotherapies have failed in established PD.
  evidence:
  - reference: PMID:38519273
    reference_title: "Brain-first vs. body-first Parkinson's disease: An update on recent evidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the initial pathology starts either in the olfactory bulb or amygdala leading to a brain-first subtype, or in the enteric nervous system leading to a body-first subtype."
    explanation: >-
      Recent review-level synthesis of human imaging, clinical, and pathology
      studies explicitly frames enteric-origin body-first PD as an alternative
      subtype within the ASOC model.
  - reference: PMID:31255487
    reference_title: "Transneuronal Propagation of Pathologic α-Synuclein from the Gut to the Brain Models Parkinson's Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Truncal vagotomy and α-syn deficiency prevented the gut-to-brain spread of α-synucleinopathy and associated neurodegeneration and behavioral deficits."
    explanation: >-
      Mouse gut-to-brain transmission experiments support the vagus nerve and
      alpha-synuclein as required components of the body-first propagation
      route.
  - reference: PMID:39241780
    reference_title: "Gut-induced alpha-Synuclein and Tau propagation initiate Parkinson's and Alzheimer's disease co-pathology and behavior impairments."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Truncal vagotomy and α-Syn deficiency significantly inhibited synucleinopathy or tauopathy spreading."
    explanation: >-
      Gut-inducible mouse models provide independent support that vagotomy and
      alpha-synuclein deficiency inhibit gut-origin propagation into the brain.
  - reference: PMID:26031848
    reference_title: "Vagotomy and subsequent risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Full truncal vagotomy is associated with a decreased risk for subsequent PD, suggesting that the vagal nerve may be critically involved in the pathogenesis of PD."
    explanation: >-
      Danish register-based cohort provides human epidemiological support that
      complete disruption of vagal afferents from the gut reduces later PD
      risk, consistent with a vagal gut-to-brain propagation route.
  - reference: PMID:28446653
    reference_title: "Vagotomy and Parkinson disease: A Swedish register-based matched-cohort study."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Overall, vagotomy was not associated with PD risk (HR 0.96, 95% CI 0.78-1.17)."
    explanation: >-
      Qualifies the vagotomy epidemiology above. In the larger Swedish register
      cohort (9,430 vagotomized patients) vagotomy as a whole showed no
      association with later Parkinson disease; the protective signal is
      confined to the truncal subgroup at long latency, so the vagotomy
      literature is weaker corroboration of a vagal gut-to-brain route than the
      subgroup hazard ratios alone imply.
  - reference: PMID:28446653
    reference_title: "Vagotomy and Parkinson disease: A Swedish register-based matched-cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Taken together, these data provide preliminary and indirect support for the Braak and prion-like hypotheses for PD prodromal development."
    explanation: >-
      The same authors grade their own truncal-vagotomy result as preliminary
      and indirect with respect to the gut-to-brain propagation hypothesis,
      which is the level of support the body-first model can currently claim
      from human surgical epidemiology.
  - reference: PMID:41105632
    reference_title: "Distinct cutaneous α-synuclein signatures in body-first and brain-first Parkinson's disease subtypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Body-first PD patients displayed a distal-to-proximal α-syn gradient (DL, 86.1% versus C7. 55.7%), contrasting with the proximal-dominant pattern in brain-first PD patients (DL, 40.5% versus C7, 50.8%)."
    explanation: >-
      Skin-biopsy pathology in 205 patients shows the distal-predominant
      cutaneous alpha-synuclein gradient predicted by a peripheral,
      autonomically distributed origin, contrasting with the proximal-dominant
      pattern of the brain-first group.
  - reference: PMID:41105632
    reference_title: "Distinct cutaneous α-synuclein signatures in body-first and brain-first Parkinson's disease subtypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Subtype classification was based on the presence of REM sleep behaviour disorder preceding motor symptoms."
    explanation: >-
      Records the circularity limit on that result: subtype membership was
      assigned from the REM-sleep-behavior-disorder proxy rather than from an
      observed origin site, so the cutaneous gradient is a correlated feature of
      the proxy-defined groups, not a direct measurement of where pathology
      began.
  - reference: PMID:27912057
    reference_title: "Gut Microbiota Regulate Motor Deficits and Neuroinflammation in a Model of Parkinson's Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "gut microbiota are required for motor deficits, microglia activation, and αSyn pathology. Antibiotic treatment ameliorates, while microbial re-colonization promotes, pathophysiology in adult animals, suggesting that postnatal signaling between the gut and the brain modulates disease."
    explanation: >-
      In α-synuclein-overexpressing mice the gut microbiota are causally
      required for α-syn pathology and motor deficits, supporting a gut-origin
      contribution to the body-first cascade.
  - reference: PMID:34334424
    reference_title: "Asymmetric Dopaminergic Dysfunction in Brain-First versus Body-First Parkinson's Disease Subtypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nigrostriatal degeneration was significantly more symmetric in patients with RBD versus patients without RBD or with unknown RBD status in both FDOPA (p = 0.001) and DaT SPECT (p = 0.001) datasets."
    explanation: >-
      Body-first (RBD+) PD shows the more symmetric nigrostriatal degeneration
      predicted by symmetric bilateral vagal propagation, differentiating it
      from brain-first PD on molecular imaging.
  - reference: PMID:27044604
    reference_title: "Evaluation of alpha-synuclein immunohistochemical methods for the detection of Lewy-type synucleinopathy in gastrointestinal biopsies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Positive alpha-synuclein staining was observed by all 5 judges in most of the slides from control cases, regardless of the staining methods that were used."
    explanation: >-
      Qualifies the model: enteric α-synuclein immunohistochemistry stains
      control gut biopsies too, so it lacks the specificity needed to establish
      enteric α-syn as a disease-defining body-first biomarker.
- hypothesis_group_id: brain_first_central_alpha_synuclein_model
  hypothesis_label: Brain-First Central α-Synuclein Initiation Model
  status: ALTERNATIVE
  description: >-
    Alpha-synuclein pathology initiates within central nervous system sites
    such as the olfactory bulb or amygdala and spreads centrifugally to
    brainstem and peripheral autonomic structures. This model best explains
    Parkinson disease presentations where central dopaminergic or olfactory
    involvement precedes prominent autonomic and enteric manifestations.
  notes: >-
    The model is supported mainly by subtype-level human imaging, clinical,
    and neuropathological patterns. It competes with, rather than refutes, the
    body-first model because both origin routes may exist within clinically
    diagnosed Parkinson disease.

    The 2026 OpenScientist hypothesis-search report
    (kb/hypotheses/Parkinsons_Disease/brain_first_central_alpha_synuclein_model)
    judges this model PARTIALLY SUPPORTED and recommends retaining ALTERNATIVE
    status. Supporting evidence is convergent at the subtype level: large-scale
    neuropathological trajectory modelling (81.9% of Lewy-body donors have
    earliest pathology in the olfactory bulb), multimodal imaging showing
    asymmetric central dopaminergic loss preceding peripheral autonomic
    denervation in RBD-negative PD, and primate/mouse olfactory-bulb PFF
    injection reproducing olfactory-to-limbic-to-brainstem spread. Key
    qualifications: (1) no prospective longitudinal human study has tracked
    α-syn pathology from a CNS origin outward; (2) RBD as a body-first proxy is
    unreliable (PSG-confirmed prevalence 17.8-62.5% by ascertainment); (3)
    structural MRI is conflicting - a 255-patient PPMI cohort found no gray
    matter volume asymmetry difference between putative subtypes; (4) dermal SAA
    cannot differentiate subtypes in established disease and origin-site is not
    yet integrated into NSD-ISS/SynNeurGe biological staging; (5) α-syn strain
    differences that might determine origin route remain uncharacterized between
    subtypes.
  evidence:
  - reference: PMID:38519273
    reference_title: "Brain-first vs. body-first Parkinson's disease: An update on recent evidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the initial pathology starts either in the olfactory bulb or amygdala leading to a brain-first subtype, or in the enteric nervous system leading to a body-first subtype."
    explanation: >-
      The ASOC model explicitly defines an olfactory bulb/amygdala origin as
      the brain-first subtype that competes with the enteric body-first route.
  - reference: PMID:38519273
    reference_title: "Brain-first vs. body-first Parkinson's disease: An update on recent evidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These subtypes should be distinguishable early in the disease course on a range of imaging, clinical, and neuropathological markers."
    explanation: >-
      Human subtype distinguishability supports representing brain-first and
      body-first disease routes as alternative mechanistic hypothesis groups.
  - reference: PMID:32830221
    reference_title: "Brain-first versus body-first Parkinson's disease: a multimodal imaging case-control study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the PDRBD- data were compatible with a brain-first trajectory, characterized by primary loss of putaminal FDOPA uptake followed by a secondary loss of cardiac MIBG signal and 11C-donepezil signal."
    explanation: >-
      Primary multimodal imaging data support a brain-first trajectory in
      RBD-negative de novo PD, where central dopaminergic dysfunction appears
      before peripheral autonomic marker loss.
  - reference: PMID:38879548
    reference_title: "Disease progression modelling reveals heterogeneity in trajectories of Lewy-type α-synuclein pathology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most donors (81.9%) show earliest pathology in the olfactory bulb, followed by accumulation in either limbic (60.8%) or brainstem (21.1%) regions."
    explanation: >-
      Data-driven neuropathological trajectory modelling of 814 brain donors
      shows olfactory-bulb-initiated (brain-first) pathology is the predominant
      spread pattern, the strongest large-scale support for a central origin.
  - reference: PMID:35989519
    reference_title: "Lewy Body Disease Primate Model with α-Synuclein Propagation from the Olfactory Bulb."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Severe α-Syn pathology was observed within the olfactory pathway and limbic system, while mild α-Syn pathology was seen in a wide range of brain regions, including the substantia nigra pars compacta, locus coeruleus, and even dorsal motor nucleus of the vagus nerve."
    explanation: >-
      Marmoset olfactory-bulb PFF injection reproduces the predicted centrifugal
      olfactory-to-limbic-to-brainstem propagation reaching the substantia nigra,
      demonstrating anatomical plausibility of a central origin.
  - reference: PMID:35943058
    reference_title: "Gray Matter Volume Loss in Proposed Brain-First and Body-First Parkinson's Disease Subtypes."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "the degree of putaminal DaT asymmetry was not associated with reduced GMV or higher GMV asymmetry. Furthermore, RBD-negative and RBD-positive patients did not demonstrate a significant difference in GMV or GMV asymmetry."
    explanation: >-
      A 255-patient PPMI structural MRI study found no gray-matter-volume
      asymmetry difference between putative brain-first and body-first PD,
      failing to support a core structural prediction of the model.
  - reference: PMID:41105632
    reference_title: "Distinct cutaneous α-synuclein signatures in body-first and brain-first Parkinson's disease subtypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Body-first PD patients displayed a distal-to-proximal α-syn gradient (DL, 86.1% versus C7. 55.7%), contrasting with the proximal-dominant pattern in brain-first PD patients (DL, 40.5% versus C7, 50.8%)."
    explanation: >-
      Skin-biopsy pathology gives the brain-first group a proximal-dominant
      cutaneous alpha-synuclein pattern with lower overall peripheral burden,
      the peripheral distribution a centrally initiated, centrifugally
      spreading process would predict.
  - reference: PMID:41714532
    reference_title: "Stage-specific interactions among PLM, RBD, and OSAHS in parkinson's disease and MSA."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MSA exhibited more severe disturbances than PD: RBD prevalence 47.1% vs 17.8%"
    explanation: >-
      Polysomnography in 264 Parkinson disease patients puts REM-sleep behavior
      disorder prevalence at 17.8%, the low end of the range that makes an
      RBD-only proxy an unstable basis for assigning brain-first versus
      body-first membership.
  - reference: PMID:29084403
    reference_title: "High Frequency of Sleep Disorders in Parkinson's Disease and Its Relationship with Quality of Life."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We observed sleep disorders in 96.5% of the participants, with REM-sleep behavior disorder found in 62.5%, obstructive sleep apnea in 62.5%, insomnia in 55.7%, and restless legs syndrome in 28.4%."
    explanation: >-
      Video-polysomnography in a separate Parkinson disease outpatient cohort
      puts REM-sleep behavior disorder prevalence at 62.5%. Read against the
      17.8% figure above, the roughly threefold spread in ascertained RBD
      prevalence is what limits an RBD-only origin-site proxy; the two cohorts
      differ in population and objectives, so the contrast bounds the proxy's
      stability rather than isolating a single ascertainment method.
  - reference: PMID:31797870
    reference_title: "Structural heterogeneity of α-synuclein fibrils amplified from patient brain extracts."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "there was a greater structural heterogeneity among α-synuclein fibrils from the PD brain compared to those from the MSA brain, possibly reflecting on the greater variability of disease phenotypes evident in PD."
    explanation: >-
      Fibrils amplified from PD brain show conformational strain heterogeneity;
      whether strain differences determine brain-first versus body-first origin
      remains uncharacterized, qualifying the mechanistic basis of the model.
- hypothesis_group_id: synaptic_vesicle_endocytosis_convergence
  hypothesis_label: Synaptic Vesicle Endocytosis Dysfunction as a Convergent PD Mechanism
  status: EMERGING
  description: >-
    A growing set of PD genes act in synaptic vesicle recycling and
    clathrin-mediated endocytosis rather than in alpha-synuclein handling
    directly: SYNJ1, DNAJC6, SH3GL2, LRRK2, VPS35, and now ITSN1. This
    hypothesis holds that disrupted presynaptic vesicle endocytosis is a
    convergence point that predisposes to PD, upstream of or parallel to
    alpha-synuclein aggregation, and that it is an early feature preceding
    overt neurodegeneration. ITSN1 is the newest entrant: rare
    protein-truncating variants carry a large odds ratio, and the fly ortholog
    interacts genetically and physically with alpha-synuclein. Open: whether
    the endocytic defect acts mainly by mishandling alpha-synuclein or by an
    independent route, and whether ITSN1's effect is specific to PD given its
    separate association with autism.
  evidence:
  - reference: PMID:40056900
    reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study adds to the growing evidence that vesicle trafficking
      dysfunction is a key driver in PD pathogenesis.
    explanation: >-
      The ITSN1 discovery paper frames its own finding as part of a
      vesicle-trafficking convergence, the claim this hypothesis groups.
  - reference: PMID:40056900
    reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Interestingly, ITSN1 appears to interact with Synaptojanin-1 (SYNJ1),
      which is associated with early-onset PD.
    explanation: >-
      Places ITSN1 in the same endocytic pathway as an established PD gene,
      supporting convergence rather than an isolated locus.
  notes: >-
    Seeded from the ITSN1 lead (Impetus Grants, Ryan Dhindsa). The
    Synaptic Dysfunction pathophysiology node already carries DNAJC6, SYNJ1 and
    ITSN1. An OpenScientist run was commissioned on this group to test whether
    the vesicle-endocytosis convergence is supported beyond the ITSN1 discovery
    paper; its assessment will be added separately.
pathophysiology:
- name: Dopaminergic Neuron Loss
  conforms_to: "parkinsonism_dopaminergic_degeneration#Nigrostriatal Dopaminergic Neurodegeneration"
  description: >
    Progressive degeneration of dopaminergic neurons in the substantia nigra
    pars compacta is the core neuropathological lesion of Parkinson's disease.
    Motor signs emerge once an estimated 60-80% of these neurons are lost and
    the resulting loss of nigrostriatal dopamine input can no longer be
    compensated.
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  locations:
  - preferred_term: substantia nigra
    term:
      id: UBERON:0002038
      label: substantia nigra
  biological_processes:
  - preferred_term: Dopamine Biosynthesis
    term:
      id: GO:0042416
      label: dopamine biosynthetic process
  downstream:
  - target: Striatal Dopamine Deficiency
    causal_link_type: DIRECT
    description: >
      Degeneration of substantia nigra pars compacta neurons removes the
      nigrostriatal projection, depleting dopamine in the striatum.
    evidence:
    - reference: PMID:28332488
      reference_title: "Parkinson disease."
      supports: SUPPORT
      snippet: "Neuronal loss in the substantia nigra, which causes striatal dopamine deficiency, and intracellular inclusions containing aggregates of α-synuclein are the neuropathological hallmarks of Parkinson disease."
      explanation: >
        This Nature Reviews Disease Primers review states that substantia nigra
        neuronal loss causes striatal dopamine deficiency, supporting this
        causal edge.
  evidence:
  - reference: PMID:37048085
    reference_title: "Microglia Mediated Neuroinflammation in Parkinson's Disease."
    supports: SUPPORT
    snippet: "Tremor, shaking, movement problems, and difficulty with balance and coordination are among the hallmarks, and dopaminergic neuronal loss in substantia nigra pars compacta of the brain and aggregation of intracellular protein α-synuclein are the pathological characterizations."
    explanation: This review confirms that dopaminergic neuronal loss in the substantia nigra pars compacta is a pathological hallmark of Parkinson's disease, supporting the core mechanism of dopaminergic neuron degeneration.
- name: Striatal Dopamine Deficiency
  biological_scale: TISSUE
  conforms_to: "parkinsonism_dopaminergic_degeneration#Striatal Dopamine Deficiency and Basal Ganglia Circuit Dysfunction"
  description: >
    Degeneration of nigrostriatal dopaminergic terminals depletes dopamine in
    the striatum, the principal input nucleus of the basal ganglia. Reduced
    striatal dopamine withdraws normal modulation of medium spiny projection
    neurons and is the proximate biochemical deficit linking nigral neuron
    loss to the motor features of Parkinson's disease.
  cell_types:
  - preferred_term: Striatal medium spiny neuron
    term:
      id: CL:1001474
      label: medium spiny neuron
  biological_processes:
  - preferred_term: Dopaminergic synaptic transmission
    term:
      id: GO:0001963
      label: synaptic transmission, dopaminergic
    modifier: DECREASED
  - preferred_term: Dopamine Secretion
    term:
      id: GO:0014046
      label: dopamine secretion
    modifier: DECREASED
  locations:
  - preferred_term: striatum
    term:
      id: UBERON:0002435
      label: striatum
  downstream:
  - target: Basal Ganglia Circuit Dysfunction
    causal_link_type: DIRECT
    description: >
      Loss of striatal dopamine unbalances the direct and indirect basal
      ganglia pathways.
    evidence:
    - reference: PMID:18781672
      reference_title: "Functional organization of the basal ganglia: therapeutic implications for Parkinson's disease."
      supports: SUPPORT
      snippet: "Dopaminergic depletion in Parkinson's disease disrupts the corticostriatal balance leading to increased activity the indirect circuit and reduced activity in the direct circuit."
      explanation: >
        This review states that dopaminergic depletion disrupts the
        corticostriatal balance, raising indirect-pathway and lowering
        direct-pathway activity, supporting striatal dopamine deficiency as the
        cause of basal ganglia circuit dysfunction.
  - target: Intestinal Tight Junction Protein Loss
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      Selective nigrostriatal dopaminergic lesioning is followed by loss of
      intestinal tight junction protein, establishing a brain-to-gut direction
      alongside the gut-to-brain chain curated elsewhere in this entry. Neither
      lesion study identifies the mediating route, whether autonomic, endocrine,
      or humoral, so the link is recorded with unknown intermediates.
    evidence:
    - reference: PMID:42732868
      reference_title: "Striatal 6-hydroxydopamine lesion in rats induces dysregulation of the gut barrier."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Together, these findings demonstrate that neurotrauma in the DA system can compromise gut integrity and microbial composition, supporting a brain-to-gut axis in PD pathophysiology"
      explanation: >
        States the edge directly. The lesion was placed in the striatum, and
        nigral dopaminergic loss was confirmed in the same animals by
        apomorphine-induced rotation and reduced tyrosine hydroxylase
        expression, so the gut findings are anchored to a verified central
        lesion rather than to the injection alone.
    - reference: PMID:37271045
      reference_title: "Nigrostriatal 6-hydroxydopamine lesions increase alpha-synuclein levels and permeability in rat colon."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "6-OHDA decreased the Zonula occludens protein 1 barrier integrity score, suggesting increased colonic permeability."
      explanation: >
        Independent replication of this edge's own outcome by a different
        group, which is what lifts it above a single-study claim. The lesion is
        nigrostriatal and the readout is the junctional protein named in the
        target node.
    - reference: PMID:37271045
      reference_title: "Nigrostriatal 6-hydroxydopamine lesions increase alpha-synuclein levels and permeability in rat colon."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "6-OHDA-induced nigrostriatal dopaminergic damage leads to increased aSyn levels and glial cell activation particularly in the colon, suggesting that the gut-brain axis interactions in PD are bidirectional and the detrimental process may start in the brain."
      explanation: >
        The authors' directional conclusion. Graded indirect for this edge
        because the consequences it names are colonic alpha-synuclein and glial
        activation rather than the junctional protein, so it supports the
        brain-to-gut direction without reporting this edge's own outcome.
  - target: Gut Microbiome Dysbiosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      The same nigrostriatal lesion shifts gram-negative bacterial classes and
      lowers short-chain fatty acid levels, so PD-associated dysbiosis is in part
      a consequence of central dopaminergic loss rather than only a proposed
      upstream trigger of it. This edge closes a feedback loop with the
      body-first chain instead of replacing it.
    evidence:
    - reference: PMID:42732868
      reference_title: "Striatal 6-hydroxydopamine lesion in rats induces dysregulation of the gut barrier."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "6-OHDA-lesioned rats also exhibited alterations in specific gram-negative bacterial classes and reduced short-chain fatty acid levels (SCFAs)."
      explanation: >
        Reports the microbial compositional and metabolite shift in the lesioned
        animals, supporting central dopaminergic injury as an upstream cause of
        the dysbiotic state and not merely a correlate of it.
  evidence:
  - reference: PMID:28332488
    reference_title: "Parkinson disease."
    supports: SUPPORT
    snippet: "Neuronal loss in the substantia nigra, which causes striatal dopamine deficiency, and intracellular inclusions containing aggregates of α-synuclein are the neuropathological hallmarks of Parkinson disease."
    explanation: >
      This review identifies striatal dopamine deficiency as a defining
      neuropathological hallmark of Parkinson's disease.
- name: Basal Ganglia Circuit Dysfunction
  description: >
    Striatal dopamine loss shifts the basal ganglia-thalamocortical motor
    circuit toward excessive inhibitory output: the indirect pathway becomes
    hyperactive and the direct pathway hypoactive, increasing inhibitory drive
    from the globus pallidus pars interna onto the motor thalamus and cortex.
    This aberrant circuit activity, rather than neuron loss alone, generates
    the cardinal motor signs of Parkinson's disease.
  cell_types:
  - preferred_term: Striatal medium spiny neuron
    term:
      id: CL:1001474
      label: medium spiny neuron
  - preferred_term: GABAergic neuron
    term:
      id: CL:0000617
      label: GABAergic neuron
  biological_processes:
  - preferred_term: GABAergic synaptic transmission
    term:
      id: GO:0051932
      label: synaptic transmission, GABAergic
    modifier: DYSREGULATED
  locations:
  - preferred_term: basal ganglia
    term:
      id: UBERON:0002420
      label: basal ganglion
  downstream:
  - target: Resting Tremor
    causal_link_type: UNKNOWN
    evidence:
    - reference: PMID:17955331
      reference_title: "The Rotterdam Study: objectives and design update."
      supports: SUPPORT
      snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
      explanation: >
        This identifies resting tremor as a cardinal parkinsonian sign; its
        precise circuit origin within basal ganglia dysfunction remains
        debated, so the edge directness is left UNKNOWN.
  - target: Bradykinesia
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:17955331
      reference_title: "The Rotterdam Study: objectives and design update."
      supports: SUPPORT
      snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
      explanation: This establishes bradykinesia as a cardinal parkinsonian sign downstream of basal ganglia circuit dysfunction.
    - reference: PMID:19127584
      reference_title: "The basal ganglia in Parkinson's disease: current concepts and unexplained observations."
      supports: SUPPORT
      snippet: "In the parkinsonian state, dopamine depletion shifts the BG toward inhibiting cortically generated movements by increasing the gain in the globus pallidus pars externa-subthalamic nucleus-globus pallidus pars interna network and reducing activity in \"direct\" cortico-putaminal-globus pallidus pars interna projections."
      explanation: >
        This review describes how parkinsonian basal ganglia circuit
        dysfunction inhibits cortically generated movements, supporting
        bradykinesia as a direct downstream consequence.
  - target: Rigidity
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:17955331
      reference_title: "The Rotterdam Study: objectives and design update."
      supports: SUPPORT
      snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
      explanation: This identifies rigidity as a cardinal parkinsonian sign downstream of basal ganglia circuit dysfunction.
    - reference: PMID:19127584
      reference_title: "The basal ganglia in Parkinson's disease: current concepts and unexplained observations."
      supports: SUPPORT
      snippet: "In the parkinsonian state, dopamine depletion shifts the BG toward inhibiting cortically generated movements by increasing the gain in the globus pallidus pars externa-subthalamic nucleus-globus pallidus pars interna network and reducing activity in \"direct\" cortico-putaminal-globus pallidus pars interna projections."
      explanation: >
        This review describes dopamine-depletion-driven basal ganglia output
        changes that inhibit cortically generated movements, supporting a
        mechanistic basal ganglia circuit contribution to parkinsonian motor
        signs including rigidity.
  - target: Postural Instability
    causal_link_type: UNKNOWN
    evidence:
    - reference: PMID:17955331
      reference_title: "The Rotterdam Study: objectives and design update."
      supports: SUPPORT
      snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
      explanation: >
        This supports impaired postural reflexes as a cardinal parkinsonian
        sign; postural instability has a recognized non-dopaminergic
        component, so the edge directness is left UNKNOWN.
  - target: Freezing of Gait
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      Freezing is attributed to global motor-circuit dysfunction arising from the
      excitatory/inhibitory imbalance within the basal ganglia, and its
      responsiveness to the dopaminergic medication cycle marks a motor
      component. The intermediates are not resolved: the same source attributes
      freezing additionally to impaired cognitive, attentional and visuospatial
      networks outside this node.
    evidence:
    - reference: PMID:42646502
      reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: "Glutamate and GABA Dysfunction | Imbalance between excitatory (glutamatergic) and inhibitory (GABAergic) signaling within the regulatory circuits of the basal ganglia, inducing excitotoxic hyperactivity. | Global motor circuit dysfunction: Incoordination, postural instability, and motor blocks (Freezing of gait)."
      explanation: >
        The review's own pathophysiology table places freezing of gait
        downstream of excitatory/inhibitory imbalance in the basal ganglia
        circuits, which is the mechanism this node carries.
    - reference: PMID:42646502
      reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      quote_role: REVIEW_SYNTHESIS
      snippet: "FOG increases fall risk and lowers quality of life, often occurring during the “off” phase of dopaminergic medication, suggesting a motor component."
      explanation: >
        Timing against the dopaminergic medication cycle is the review's own
        argument that freezing has a motor-circuit component; it is an
        inference from treatment response rather than a direct observation of
        the circuit.
  evidence:
  - reference: PMID:18781672
    reference_title: "Functional organization of the basal ganglia: therapeutic implications for Parkinson's disease."
    supports: SUPPORT
    snippet: "The parkinsonian state is characterized by disruption of the internal balance of the BG leading to hyperactivity in the two main entry points of the network (striatum and STN) and excessive inhibitory output from the GPi."
    explanation: >
      This review characterizes the parkinsonian basal ganglia by disrupted
      internal balance and excessive inhibitory GPi output, supporting basal
      ganglia circuit dysfunction as a distinct mechanism node.
  - reference: PMID:30897356
    reference_title: "Circuit Mechanisms of Parkinson's Disease."
    supports: SUPPORT
    snippet: "We will then describe the basal ganglia-thalamocortical circuit, the major locus of PD-related circuit dysfunction, and some of the models that have influenced its study."
    explanation: >
      This review identifies the basal ganglia-thalamocortical circuit as the
      major locus of PD-related circuit dysfunction.
- name: Alpha-Synuclein Aggregation
  conforms_to: "parkinsonism_dopaminergic_degeneration#Alpha-Synuclein Aggregation and Lewy Pathology"
  description: >
    Misfolded alpha-synuclein protein accumulates to form Lewy bodies and
    Lewy neurites. These aggregates spread through the nervous system in a
    prion-like manner, contributing to neurodegeneration.
  biological_processes:
  - preferred_term: inclusion body assembly
    term:
      id: GO:0070841
      label: inclusion body assembly
  downstream:
  - target: Dopaminergic Neuron Loss
    evidence:
    - reference: PMID:38245249
      reference_title: "The pathogenesis of Parkinson's disease."
      supports: SUPPORT
      snippet: "Biochemical studies, investigation of transplanted neurons in patients with Parkinson's disease, and cell and animal model studies suggest that abnormal aggregation of α-synuclein and spreading of pathology between the gut, brainstem, and higher brain regions probably underlie the development and progression of Parkinson's disease."
      explanation: This indicates that α-synuclein aggregation drives disease development and progression, supporting downstream dopaminergic neuron loss.
  - target: Neuroinflammation
    evidence:
    - reference: PMID:36598534
      reference_title: "Role of α-synuclein in microglia: autophagy and phagocytosis balance neuroinflammation in Parkinson's disease."
      supports: SUPPORT
      snippet: "α-Syn is a crucial marker of PD, and its accumulation leads to microglia M1-like phenotype polarization, activation of NLRP3 inflammasomes, and impaired autophagy and phagocytosis in microglia."
      explanation: This links α-synuclein accumulation to microglial activation, supporting neuroinflammation as a downstream effect.
  - target: Nigral Cellular Senescence
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Alpha-synuclein pathology is one of the two recorded routes into the nigral senescence node.
      Injected preformed fibrils drive the senescence marker changes in mouse glia, and reduced
      SATB1 protein in human PD midbrain connects that pathology to the dopaminergic-neuron arm of
      the same node. What links fibril uptake to the arrest is not established.
    evidence:
    - reference: PMID:34359864
      reference_title: "Alpha-Synuclein Preformed Fibrils Induce Cellular Senescence in Parkinson's Disease Models."
      supports: SUPPORT
      directness: DIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Our results demonstrate that α-syn PFF-induced toxicity reduces the levels of Lamin B1 and HMGB1, both established markers of cellular senescence, in correlation with an increase in the levels of p21, a cell cycle-arrester and senescence marker, in both reactive astrocytes and microglia in mouse brains."
      explanation: >-
        Alpha-synuclein fibrils shift the same three markers that this entry's senescence node
        describes, in astrocytes and microglia of injected mouse brain. Mouse work, so it carries
        the direction of the edge without establishing it in patients.
  evidence:
  - reference: PMID:38245249
    reference_title: "The pathogenesis of Parkinson's disease."
    supports: SUPPORT
    snippet: "Parkinson's disease is a progressive neurodegenerative condition associated with the deposition of aggregated α-synuclein."
    explanation: This authoritative Lancet review establishes that aggregated α-synuclein deposition is a defining feature of Parkinson's disease pathogenesis.
  - reference: PMID:38245249
    reference_title: "The pathogenesis of Parkinson's disease."
    supports: SUPPORT
    snippet: "Biochemical studies, investigation of transplanted neurons in patients with Parkinson's disease, and cell and animal model studies suggest that abnormal aggregation of α-synuclein and spreading of pathology between the gut, brainstem, and higher brain regions probably underlie the development and progression of Parkinson's disease."
    explanation: This provides direct evidence for the prion-like spreading mechanism of α-synuclein pathology across neural networks, supporting the mechanism of trans-neuronal propagation.
  - reference: PMID:36598534
    reference_title: "Role of α-synuclein in microglia: autophagy and phagocytosis balance neuroinflammation in Parkinson's disease."
    supports: SUPPORT
    snippet: "Parkinson's disease (PD) is the second most common neurodegenerative disease, and is characterized by accumulation of α-synuclein (α-syn)."
    explanation: Confirms that α-synuclein accumulation is a key pathological characterization of PD, reinforcing the central role of protein aggregation in disease pathology.
- name: Mitochondrial Dysfunction
  conforms_to:
  - "parkinsonism_dopaminergic_degeneration#Mitochondrial Complex I Inhibition and Oxidative Stress"
  - "mitochondrial_dysfunction#Bioenergetic Decline and Oxidative Stress"
  - "mitochondrial_dysfunction#Impaired Mitophagy and Quality Control"
  description: >
    Impaired mitochondrial function, particularly complex I deficiency,
    leads to oxidative stress and neuronal death. Multiple PD genes
    (PINK1, Parkin, DJ-1) regulate mitochondrial quality control.
  genes:
  - preferred_term: PINK1
    term:
      id: hgnc:14581
      label: PINK1
  - preferred_term: PRKN
    term:
      id: hgnc:8607
      label: PRKN
  - preferred_term: FBXO7
    term:
      id: hgnc:13586
      label: FBXO7
  - preferred_term: VPS13C
    term:
      id: hgnc:23594
      label: VPS13C
  - preferred_term: CHCHD2
    term:
      id: hgnc:21645
      label: CHCHD2
  biological_processes:
  - preferred_term: mitochondrion organization
    term:
      id: GO:0007005
      label: mitochondrion organization
  - preferred_term: Oxidative phosphorylation (complex I deficiency)
    term:
      id: GO:0006119
      label: oxidative phosphorylation
    modifier: DECREASED
  - preferred_term: Mitophagy (PINK1/Parkin quality control)
    term:
      id: GO:0000422
      label: autophagy of mitochondrion
    modifier: DECREASED
  - preferred_term: Reactive oxygen species metabolism (oxidative stress)
    term:
      id: GO:0072593
      label: reactive oxygen species metabolic process
    modifier: INCREASED
  downstream:
  - target: Dopaminergic Neuron Loss
    evidence:
    - reference: PMID:27911343
      reference_title: "PINK1, Parkin, and Mitochondrial Quality Control: What can we Learn about Parkinson's Disease Pathobiology?"
      supports: SUPPORT
      snippet: "For the past 30 years, mitochondrial dysfunction has been hypothesized to play a central role in the pathobiology of this devastating neurodegenerative disease."
      explanation: This supports mitochondrial dysfunction as a central driver of neurodegeneration in PD, consistent with dopaminergic neuron loss.
  evidence:
  - reference: PMID:38245249
    reference_title: "The pathogenesis of Parkinson's disease."
    supports: SUPPORT
    snippet: "At a cellular level, abnormal mitochondrial, lysosomal, and endosomal function can be identified in both monogenic and sporadic Parkinson's disease, suggesting multiple potential treatment approaches."
    explanation: This establishes that mitochondrial dysfunction is a common cellular feature across both genetic and sporadic forms of PD, supporting its central role in disease pathogenesis.
  - reference: PMID:25611507
    reference_title: "The roles of PINK1, parkin, and mitochondrial fidelity in Parkinson's disease."
    supports: SUPPORT
    snippet: "Biochemical and genetic studies reveal that the products of two genes that are mutated in autosomal recessive parkinsonism, PINK1 and Parkin, normally work together in the same pathway to govern mitochondrial quality control, bolstering previous evidence that mitochondrial damage is involved in Parkinson's disease."
    explanation: This directly supports the role of PINK1 and Parkin genes in mitochondrial quality control and confirms that mitochondrial damage is involved in PD pathogenesis.
  - reference: PMID:27911343
    reference_title: "PINK1, Parkin, and Mitochondrial Quality Control: What can we Learn about Parkinson's Disease Pathobiology?"
    supports: SUPPORT
    snippet: "For the past 30 years, mitochondrial dysfunction has been hypothesized to play a central role in the pathobiology of this devastating neurodegenerative disease. The identifications of mutations in genes encoding PINK1 (PTEN-induced kinase 1) and Parkin (E3 ubiquitin ligase) in familial PD and their functional association with mitochondrial quality control provided further support to this hypothesis."
    explanation: This review confirms the long-standing central role of mitochondrial dysfunction in PD and validates the connection between PINK1/Parkin mutations and mitochondrial quality control defects.
  - reference: PMID:2154550
    reference_title: "Mitochondrial complex I deficiency in Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These results indicated a specific defect of Complex I activity in the substantia nigra of patients with Parkinson's disease."
    explanation: Direct human postmortem evidence of substantia nigra complex I deficiency in Parkinson's disease, anchoring the node's human relevance beyond the rotenone animal model.
  - reference: PMID:23933751
    reference_title: "The Parkinson's disease-linked proteins Fbxo7 and Parkin interact to mediate mitophagy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Cells with reduced Fbxo7 expression showed deficiencies in translocation of Parkin to mitochondria, ubiquitination of mitofusin 1 and mitophagy."
    explanation: Supports binding FBXO7 to this node, by showing that reduced FBXO7 impairs the parkin-dependent mitophagy step the node describes.
  - reference: PMID:26942284
    reference_title: Loss of VPS13C Function in Autosomal-Recessive Parkinsonism Causes Mitochondrial Dysfunction and Increases PINK1/Parkin-Dependent Mitophagy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Silencing of VPS13C was associated with lower mitochondrial membrane potential, mitochondrial fragmentation, increased respiration rates, exacerbated PINK1/Parkin-dependent mitophagy, and transcriptional upregulation of PARK2 in response to mitochondrial damage."
    explanation: Supports binding VPS13C to this node, by showing that VPS13C loss lowers mitochondrial membrane potential and fragments mitochondria.
  - reference: PMID:28589937
    reference_title: "Loss of Parkinson's disease-associated protein CHCHD2 affects mitochondrial crista structure and destabilizes cytochrome c."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The loss of CHCHD2 in Drosophila causes abnormal matrix structures and impaired oxygen respiration in mitochondria, leading to oxidative stress, dopaminergic neuron loss and motor dysfunction with age."
    explanation: Supports binding CHCHD2 to this node, and links its loss to the dopaminergic neuron loss this node feeds.
- name: PGC-1alpha Transcriptional Program Repression
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >
    Reduced activity of the PPARGC1A-encoded transcriptional coactivator
    PGC-1alpha downregulates the nuclear-encoded bioenergetic program it
    drives - mitochondrial biogenesis, respiratory-chain subunit expression,
    and antioxidant defenses - in nigral dopaminergic neurons. Two routes
    converge on this node. In the parkin-dependent route, loss of parkin E3
    ligase function allows its substrate PARIS (ZNF746) to accumulate and
    transcriptionally repress the PPARGC1A promoter. In sporadic disease,
    PGC-1alpha-responsive bioenergetic gene sets are already underexpressed
    in laser-captured human nigral dopaminergic neurons at subclinical
    stages, placing this lesion early in the cascade rather than as a
    terminal consequence of neuron loss. The therapeutic corollary is not
    symmetric: restoring PGC-1alpha rescues dopaminergic neurons in cellular
    models, but sustained supraphysiological expression is itself toxic to
    the nigrostriatal system (see the HUMAN_MODEL_MISMATCH discussion
    pd_pgc1a_therapeutic_window).
  molecular_functions:
  - preferred_term: transcription coactivator activity
    term:
      id: GO:0003713
      label: transcription coactivator activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: mitochondrial biogenesis program
    term:
      id: GO:0007005
      label: mitochondrion organization
    modifier: DECREASED
  cell_types:
  - preferred_term: nigral dopaminergic neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  downstream:
  - target: Mitochondrial Dysfunction
    causal_link_type: DIRECT
    description: >
      Loss of PGC-1alpha coactivation lowers expression of nuclear-encoded
      respiratory-chain subunits, producing the electron-transport deficit
      already curated on the Mitochondrial Dysfunction node.
    evidence:
    - reference: PMID:20926834
      reference_title: "PGC-1α, a potential therapeutic target for early intervention in Parkinson's disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "These gene sets pinpoint defects in mitochondrial electron transport, glucose utilization, and glucose sensing and reveal that they occur early in disease pathogenesis."
      explanation: >
        A meta-analysis of 185 laser-captured human dopaminergic neuron and
        substantia nigra transcriptomes places the PGC-1alpha-responsive
        bioenergetic deficit upstream of, and early relative to, overt
        mitochondrial failure.
    - reference: PMID:20926834
      reference_title: "PGC-1α, a potential therapeutic target for early intervention in Parkinson's disease."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Activation of PGC-1α results in increased expression of nuclear-encoded subunits of the mitochondrial respiratory chain and blocks the dopaminergic neuron loss induced by mutant α-synuclein or the pesticide rotenone in cellular disease models."
      explanation: >
        Rescue in the opposite direction - restoring PGC-1alpha raises
        respiratory-chain subunit expression and prevents dopaminergic loss
        in cellular models - supports the direction of this causal edge.
  - target: Oxidative Stress
    causal_link_type: DIRECT
    description: >
      PGC-1alpha coordinates the antioxidant arm of the mitochondrial stress
      response, so its repression lowers reactive-oxygen-species buffering
      capacity in nigral neurons.
    evidence:
    - reference: PMID:42430091
      reference_title: "The Role of PGC-1α in Neurodegenerative Diseases: Molecular Mechanisms, Translational Challenges, and Therapeutic Potential."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Current findings indicate that PGC-1α supports mitochondrial biogenesis, oxidative phosphorylation, antioxidant defense, mitophagy, autophagy, protein quality control, and inflammatory balance."
      explanation: >
        Review evidence that antioxidant defense is part of the PGC-1alpha
        output program, which is the basis for the edge to Oxidative Stress.
  evidence:
  - reference: PMID:21376232
    reference_title: "PARIS (ZNF746) repression of PGC-1α contributes to neurodegeneration in Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PARIS is a KRAB and zinc finger protein that accumulates in models of parkin inactivation and in human PD brain."
    explanation: >
      Establishes that the repressor upstream of PGC-1alpha accumulates in
      human Parkinson disease brain, not only in experimental models.
  - reference: PMID:21376232
    reference_title: "PARIS (ZNF746) repression of PGC-1α contributes to neurodegeneration in Parkinson's disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Conditional knockout of parkin in adult animals leads to progressive loss of dopamine (DA) neurons in a PARIS-dependent manner."
    explanation: >
      Genetic epistasis in adult conditional parkin knockout mice shows the
      dopaminergic loss is routed through PARIS, the PPARGC1A repressor.
  - reference: PMID:20926834
    reference_title: "PGC-1α, a potential therapeutic target for early intervention in Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genes controlling cellular bioenergetics that are expressed in response to peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) are underexpressed in Parkinson's disease patients."
    explanation: >
      Direct human transcriptomic evidence that the PGC-1alpha-responsive
      program is underexpressed in Parkinson disease, which is the claim this
      node asserts.
  notes: >
    PPARGC1A is deliberately not added to the `genetic` section: it is not an
    established Mendelian Parkinson disease gene, but a downstream
    transcriptional node reached from PRKN (via PARIS/ZNF746) and, in
    sporadic disease, from as-yet-unresolved upstream regulation.
- name: MAPK Dysregulation
  description: >
    Dysregulation of mitogen-activated protein kinase (MAPK) signaling, particularly
    through overactivation of the JNK and p38 cascades, accelerates neurodegeneration
    and promotes alpha-synuclein accumulation and microglial activation. While basal
    MAPK activity is essential for neuroprotection and neuronal growth, pathological
    MAPK overactivation inhibits neuroprotective PI3K/AKT and PP2A pathways and
    activates detrimental GSK-3β and PTEN signaling, driving dopaminergic neurotoxicity.
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  - preferred_term: Microglia
    term:
      id: CL:0000129
      label: microglial cell
  biological_processes:
  - preferred_term: MAPK cascade
    term:
      id: GO:0000165
      label: MAPK cascade
    modifier: INCREASED
  - preferred_term: JNK cascade
    term:
      id: GO:0007254
      label: JNK cascade
    modifier: INCREASED
  - preferred_term: p38MAPK cascade
    term:
      id: GO:0038066
      label: p38MAPK cascade
    modifier: INCREASED
  downstream:
  - target: Alpha-Synuclein Aggregation
    description: MAPK dysregulation promotes alpha-synuclein accumulation.
    evidence:
    - reference: PMID:42320726
      reference_title: "Molecular crosstalk between MAPK signaling and neuroprotective pathways in Parkinson's disease: from pathogenesis to therapeutic potential."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "detailing how its dysregulation promotes the accumulation of alpha-synuclein and the activation of microglia"
      explanation: >
        The paper identifies MAPK dysregulation as promoting alpha-synuclein accumulation, supporting this downstream causal link.
  - target: Neuroinflammation
    description: MAPK overactivation drives microglial activation and pro-inflammatory cytokine release.
    evidence:
    - reference: PMID:42320726
      reference_title: "Molecular crosstalk between MAPK signaling and neuroprotective pathways in Parkinson's disease: from pathogenesis to therapeutic potential."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "detailing how its dysregulation promotes the accumulation of alpha-synuclein and the activation of microglia"
      explanation: >
        The paper identifies MAPK dysregulation as promoting microglial activation, a key driver of neuroinflammation in PD.
  - target: Dopaminergic Neuron Loss
    description: MAPK-driven oxidative stress, impaired neuroprotection, and neuroinflammation converge to promote dopaminergic neurotoxicity.
    evidence:
    - reference: PMID:42320726
      reference_title: "Molecular crosstalk between MAPK signaling and neuroprotective pathways in Parkinson's disease: from pathogenesis to therapeutic potential."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Preclinical evidence strongly supports the use of MAPK inhibitors to mitigate dopaminergic neurotoxicity and reduce proinflammatory cytokine release"
      explanation: >
        The paper's discussion of MAPK inhibitors as a strategy to reduce dopaminergic neurotoxicity indicates that MAPK dysregulation drives neuronal loss.
  evidence:
  - reference: PMID:42320726
    reference_title: "Molecular crosstalk between MAPK signaling and neuroprotective pathways in Parkinson's disease: from pathogenesis to therapeutic potential."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "While basal MAPK activity is essential for neuroprotection and neuronal growth, its overactivation, specifically via the JNK and p38 cascades, accelerates neurodegeneration."
    explanation: >
      This review establishes MAPK/JNK/p38 overactivation as a central driver of PD neurodegeneration, providing strong evidence for MAPK dysregulation as a distinct pathophysiological node.
  - reference: PMID:42320726
    reference_title: "Molecular crosstalk between MAPK signaling and neuroprotective pathways in Parkinson's disease: from pathogenesis to therapeutic potential."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "highlights critical crosstalk between MAPK and other vital pathways, including the inhibition of the neuroprotective PI3K/AKT and PP2A pathways and the detrimental activation of GSK-3β and PTEN signaling."
    explanation: >
      This describes the broader signaling context of MAPK dysregulation, including inhibition of neuroprotective and activation of pro-degenerative pathways.
- name: Neuroinflammation
  description: >
    Sustained glial activation in the PD brain, driven principally by microglia,
    with pro-inflammatory cytokine release (TNF-α, IL-1β, IL-6), M1-like phenotype
    polarization, and complement cascade activation. Reactive astrocytes feed this
    state through their own release of inflammatory mediators; that arm is modeled
    separately as Reactive Astrogliosis.
  conforms_to:
  - "neuroinflammation_glial_activation#Reactive Microglial and Astrocytic Activation"
  - "neuroinflammation_glial_activation#Proinflammatory Cytokine and Chemokine Release"
  cell_types:
  - preferred_term: Microglia
    term:
      id: CL:0000129
      label: microglial cell
  - preferred_term: Astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: Microglial activation
    term:
      id: GO:0001774
      label: microglial cell activation
    modifier: INCREASED
  - preferred_term: TNF-alpha production
    term:
      id: GO:0032640
      label: tumor necrosis factor production
    modifier: INCREASED
  - preferred_term: IL-1beta production
    term:
      id: GO:0032611
      label: interleukin-1 beta production
    modifier: INCREASED
  - preferred_term: IL-6 production
    term:
      id: GO:0032635
      label: interleukin-6 production
    modifier: INCREASED
  downstream:
  - target: Dopaminergic Neuron Loss
    evidence:
    - reference: PMID:37048085
      reference_title: "Microglia Mediated Neuroinflammation in Parkinson's Disease."
      supports: SUPPORT
      snippet: "Neuroinflammation has emerged as an involving mechanism at the initiation and development of PD."
      explanation: This indicates neuroinflammation contributes to PD progression, supporting dopaminergic neuron loss downstream.
    - reference: PMID:15668962
      reference_title: "Microglial activation and dopamine terminal loss in early Parkinson's disease."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "In vivo demonstration of parallel changes in microglial activation and corresponding dopaminergic terminal loss in the affected nigrostriatal pathway in early PD supports that neuroinflammatory responses by intrinsic microglia contribute significantly to the progressive degeneration process of the disease"
      explanation: >-
        In 10 early, drug-naive PD patients, midbrain microglial activation measured by
        [11C](R)-PK11195 PET rose as putaminal dopamine transporter binding fell and as motor
        severity worsened. The authors read this as microglia contributing to the degeneration, but
        the data are a correlation, so they support the edge to dopaminergic neuron loss only
        indirectly.
    - reference: PMID:16182554
      reference_title: "In vivo imaging of microglial activation with [11C](R)-PK11195 PET in idiopathic Parkinson's disease."
      supports: REFUTE
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "Levels of microglial activation did not correlate with clinical severity or putamen ... dopa uptake."
      explanation: >-
        In 18 PD patients, PET microglial activation did not track putaminal dopaminergic function or
        clinical severity, and stayed stable over 2 years in 8 patients followed. This argues against
        a simple dose-response link between microglial activation and ongoing dopaminergic loss, and
        is the opposite of the correlation reported in PMID:15668962.
  - target: Complement C3-C3aR Activation in Depression
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      Microglial neuroinflammation drives complement cascade activation (C3-C3aR axis) as part of
      the broader innate immune response, with convergent upregulation of complement and coagulation
      pathways in depression associated with PD. This complement-mediated branch contributes to
      depression-like behavior via microglial synaptic pruning, distinct from dopaminergic motor pathology.
    evidence:
    - reference: PMID:42263400
      reference_title: "The complement C3-microglial axis in depression of Parkinson's disease: from mechanism to therapeutic intervention."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In MPTP-treated male and female mice, hippocampal complement components (C1Q, C3, C3aR) and downstream signalling (p-STAT3, p-P65) were elevated, accompanied by microglial synapse phagocytosis and depressive-like behaviours."
      explanation: Mouse model demonstrates that neuroinflammatory upregulation of complement cascades drives hippocampal complement component elevation and microglial synaptic engulfment, manifesting as depressive-like behavior independent of motor phenotype.
  evidence:
  - reference: PMID:38245249
    reference_title: "The pathogenesis of Parkinson's disease."
    supports: SUPPORT
    snippet: "Recent work has also highlighted maladaptive immune and inflammatory responses, possibly triggered in the gut, that accelerate the pathogenesis of Parkinson's disease."
    explanation: This establishes that maladaptive immune and inflammatory responses play an active role in accelerating PD pathogenesis, supporting the neuroinflammation mechanism.
  - reference: PMID:37048085
    reference_title: "Microglia Mediated Neuroinflammation in Parkinson's Disease."
    supports: SUPPORT
    snippet: "Neuroinflammation has emerged as an involving mechanism at the initiation and development of PD. It is a complex network of interactions comprising immune and non-immune cells in addition to mediators of the immune response. Microglia, the resident macrophages in the CNS, take on the leading role in regulating neuroinflammation and maintaining homeostasis."
    explanation: This directly supports the role of microglia-mediated neuroinflammation in PD initiation and progression, confirming the importance of microglial activation in disease pathology.
  - reference: PMID:36598534
    reference_title: "Role of α-synuclein in microglia: autophagy and phagocytosis balance neuroinflammation in Parkinson's disease."
    supports: SUPPORT
    snippet: "Neuroinflammation driven by microglia is an important pathological manifestation of PD. α-Syn is a crucial marker of PD, and its accumulation leads to microglia M1-like phenotype polarization, activation of NLRP3 inflammasomes, and impaired autophagy and phagocytosis in microglia."
    explanation: This links α-synuclein accumulation to microglial activation and pro-inflammatory M1 phenotype polarization, supporting the mechanism by which neuroinflammation contributes to neurodegeneration in PD.
  - reference: PMID:3399080
    reference_title: "Reactive microglia are positive for HLA-DR in the substantia nigra of Parkinson's and Alzheimer's disease brains."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We detected large numbers of HLA-DR-positive reactive microglia (macrophages), along with Lewy bodies and free melanin, in the substantia nigra of all cases studied with Parkinson's disease (5) and parkinsonism with dementia (PD) (5)."
    explanation: >-
      Post-mortem tissue shows reactive microglia in the substantia nigra in every PD case examined,
      against one of 11 age-matched controls. This is the primary neuropathological observation of
      microglial activation in PD.
  - reference: PMID:16182554
    reference_title: "In vivo imaging of microglial activation with [11C](R)-PK11195 PET in idiopathic Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Compared to 11 normal controls, the PD patients showed significantly increased mean levels of ... binding in the pons, basal ganglia and frontal and temporal cortical regions."
    explanation: >-
      [11C](R)-PK11195 PET in 18 living PD patients shows increased binding of this marker of
      activated microglia across subcortical and cortical regions, extending the post-mortem
      finding to living patients.
  - reference: PMID:8015728
    reference_title: "Tumor necrosis factor-alpha (TNF-alpha) increases both in the brain and in the cerebrospinal fluid from parkinsonian patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The concentrations of TNF-alpha in the brain and CSF were significantly higher in parkinsonian patients than those in controls."
    explanation: Direct measurement in PD striatum and CSF supports the node's increased TNF-alpha production.
  - reference: PMID:7700568
    reference_title: "Interleukin-1 beta, interleukin-6, epidermal growth factor and transforming growth factor-alpha are elevated in the brain from parkinsonian patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The concentrations of IL-1 beta, IL-6, EGF, and TGF-alpha in the dopaminergic, striatal regions were significantly higher in parkinsonian patients than those in controls, whereas those in the cerebral cortex did not show significant differences between parkinsonian and control subjects."
    explanation: >-
      Direct measurement in PD brain supports increased IL-1beta and IL-6 production, limited to the
      dopaminergic striatal regions. The authors suggest the rise may be partly compensatory, so this
      supports the elevated cytokines but not that they are only harmful.
- name: Reactive Astrogliosis
  biological_scale: CELLULAR
  description: >
    Conversion of astrocytes from a homeostatic, broadly neuroprotective state —
    neurotrophic factor secretion, blood-brain barrier regulation, and
    water-electrolyte and glutamate homeostasis — to a reactive state that releases
    inflammatory mediators, fails to clear synaptic glutamate, and triggers
    oxidative stress. Studies indicate that mutations in PD-associated genes may
    induce functional alterations in astrocytes; the cited review names no
    individual genes, so no per-gene claim is made here. Whether astrocytes protect
    or accelerate dopaminergic degeneration is regulated by bidirectional
    astrocyte-neuron and astrocyte-glia crosstalk.
  cell_types:
  - preferred_term: Astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: Astrocyte activation
    term:
      id: GO:0048143
      label: astrocyte activation
    modifier: INCREASED
  - preferred_term: Astrocytic clearance of synaptic glutamate
    term:
      id: GO:0098712
      label: L-glutamate import across plasma membrane
    modifier: DECREASED
  downstream:
  - target: Dopaminergic Neuron Loss
    evidence:
    - reference: PMID:42599550
      reference_title: "Astrocytes orchestrate neuroprotection and pathogenesis via bidirectional neuronal interactions in Parkinson's disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Activated astrocytes accelerate neuronal degeneration by releasing inflammatory mediators, disrupting glutamate homeostasis, and triggering oxidative stress."
      explanation: States that reactive astrocytes accelerate neuronal degeneration, which is the edge this asserts.
  - target: Neuroinflammation
    description: >
      Reactive astrocytes release inflammatory mediators, adding an astrocytic arm
      to the glial inflammatory state that microglia principally drive.
    evidence:
    - reference: PMID:42599550
      reference_title: "Astrocytes orchestrate neuroprotection and pathogenesis via bidirectional neuronal interactions in Parkinson's disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Activated astrocytes accelerate neuronal degeneration by releasing inflammatory mediators, disrupting glutamate homeostasis, and triggering oxidative stress."
      explanation: Names release of inflammatory mediators as a mechanism of activated astrocytes, supporting the edge into the neuroinflammatory node.
  - target: Oxidative Stress
    evidence:
    - reference: PMID:42599550
      reference_title: "Astrocytes orchestrate neuroprotection and pathogenesis via bidirectional neuronal interactions in Parkinson's disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Activated astrocytes accelerate neuronal degeneration by releasing inflammatory mediators, disrupting glutamate homeostasis, and triggering oxidative stress."
      explanation: Names triggering of oxidative stress as a mechanism of activated astrocytes.
  - target: Blood-Brain Barrier Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      Astrocytes are one of the cell types regulating the blood-brain barrier, so
      loss of that homeostatic function on reactive conversion is a route into
      barrier breakdown. The cited review establishes the astrocytic BBB-regulatory
      role but does not itself report barrier breakdown caused by reactive
      astrocytes, so this edge is left uncited rather than over-claimed.
  evidence:
  - reference: PMID:42599550
    reference_title: "Astrocytes orchestrate neuroprotection and pathogenesis via bidirectional neuronal interactions in Parkinson's disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Recent studies indicate that mutations in PD-associated genes may induce functional alterations in astrocytes."
    explanation: Supports a genetic contribution to astrocyte dysfunction in PD, hedged as "may induce functional alterations" and naming no individual gene.
  - reference: PMID:42599550
    reference_title: "Astrocytes orchestrate neuroprotection and pathogenesis via bidirectional neuronal interactions in Parkinson's disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Furthermore, bidirectional regulatory interactions exist between astrocytes and both dopaminergic neurons and other glial cells in PD."
    explanation: Identifies bidirectional astrocyte-neuron and astrocyte-glia crosstalk as the regulator of which arm predominates.
- name: Complement C3-C3aR Activation in Depression
  description: >
    Elevated complement cascade activation, particularly the C3-C3aR signaling axis,
    drives microglial synaptic engulfment and loss. In depression associated with
    Parkinson disease, hippocampal complement components (C1Q, C3, C3aR) and downstream
    signaling (p-STAT3, p-P65) are upregulated, promoting microglial phagocytosis of
    synapses and contributing to depressive symptoms. This represents a distinct
    complement-mediated pathogenic pathway in depression, separable from canonical
    dopaminergic motor circuit involvement.
  cell_types:
  - preferred_term: Microglia
    term:
      id: CL:0000129
      label: microglial cell
  locations:
  - preferred_term: hippocampal formation
    term:
      id: UBERON:0002421
      label: hippocampal formation
  biological_processes:
  - preferred_term: complement activation
    term:
      id: GO:0006956
      label: complement activation
    modifier: INCREASED
  - preferred_term: synapse pruning
    term:
      id: GO:0098883
      label: synapse pruning
    modifier: INCREASED
  downstream:
  - target: Depression
    causal_link_type: DIRECT
    description: >
      Complement C3-C3aR-mediated microglial synaptic engulfment leads to hippocampal
      synaptic loss and dysfunction, manifesting as depression and mood disturbance
      in Parkinson disease.
    evidence:
    - reference: PMID:42263400
      reference_title: "The complement C3-microglial axis in depression of Parkinson's disease: from mechanism to therapeutic intervention."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In MPTP-treated male and female mice, hippocampal complement components (C1Q, C3, C3aR) and downstream signalling (p-STAT3, p-P65) were elevated, accompanied by microglial synapse phagocytosis and depressive-like behaviours. Genetic deletion of C3 rescued both MPTP-induced motor and depressive-like behavioural deficits and prevented hippocampal synaptic loss associated with microglial synaptic engulfment."
      explanation: >
        Elevation of hippocampal complement components strongly correlates with microglial
        synaptic phagocytosis and depressive-like behaviors in MPTP mice. C3 deletion
        rescued depressive deficits and prevented synaptic loss, demonstrating causal
        linkage of complement activation to depression in PD models.
  evidence:
  - reference: PMID:42263400
    reference_title: "The complement C3-microglial axis in depression of Parkinson's disease: from mechanism to therapeutic intervention."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In MPTP-treated male and female mice, hippocampal complement components (C1Q, C3, C3aR) and downstream signalling (p-STAT3, p-P65) were elevated, accompanied by microglial synapse phagocytosis and depressive-like behaviours."
    explanation: >
      MPTP mouse model demonstrates upregulation of complement cascade components in
      hippocampus alongside microglial synaptic phagocytosis and depression-like behaviors,
      establishing the complement pathway as a mechanism driving depression in PD.
  - reference: PMID:42263400
    reference_title: "The complement C3-microglial axis in depression of Parkinson's disease: from mechanism to therapeutic intervention."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "DPD exhibits distinct sex-specific immune signatures, with convergent complement pathway activation driving microglial synaptic pruning and depressive symptoms."
    explanation: >
      Human plasma proteomic analysis from PPMI cohort reveals that depression in PD
      exhibits sex-specific complement pathway dysregulation, establishing complement
      activation as a mechanism contributing to depressive symptoms.
  - reference: PMID:42263400
    reference_title: "The complement C3-microglial axis in depression of Parkinson's disease: from mechanism to therapeutic intervention."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The antidepressant effect of BoNT/A is mediated through inhibition of the C3-C3aR signalling axis."
    explanation: >
      Mouse model studies demonstrate that complement pathway inhibition (via BoNT/A
      blocking C3-C3aR signaling) alleviates depressive-like symptoms and reduces
      microglial synaptic engulfment, providing mechanistic validation of C3-C3aR
      as a therapeutic target in depression.
- name: Serotonergic Raphe Neuron Loss
  biological_scale: CELLULAR
  description: >
    Degeneration of serotonergic neurons in the raphe nuclei removes serotonergic
    modulation of limbic circuitry. This is a non-dopaminergic arm of the
    neurodegeneration and is the mechanism the reviewed literature attributes the
    neuropsychiatric non-motor symptoms to, distinguishing them from the motor
    signs produced by nigrostriatal dopamine loss.
  cell_types:
  - preferred_term: serotonergic neuron
    term:
      id: CL:0000850
      label: serotonergic neuron
  locations:
  - preferred_term: raphe nuclei
    term:
      id: UBERON:0004684
      label: raphe nuclei
  downstream:
  - target: Anxiety
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      Loss of serotonergic modulation of limbic and fear circuitry is the route
      by which PD neuropathology is reported to promote anxiety. The
      intermediates within those circuits are not resolved in the cited source.
    evidence:
    - reference: PMID:42646502
      reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: "Serotonin ↓ | Impairment and loss of serotonergic neurons within the raphe nuclei, which are responsible for modulating the limbic circuits and circadian rhythms. | Neuropsychiatric and vegetative symptoms: Depression, anxiety, sleep fragmentation, and sleep disturbances."
      explanation: >
        The review's own pathophysiology table places anxiety downstream of
        raphe serotonergic neuron loss acting through limbic circuits, which is
        the mechanism this node carries.
    - reference: PMID:42646502
      reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: "Changes in anxiety to changes in hypothesized fear and limbic circuits were reported, suggesting PD neuropathology interacts with these pathways to promote anxiety."
      explanation: >
        Corroborates the limbic route, but the source states it as a
        hypothesized circuit correlation rather than a demonstrated mechanism,
        so the quote reaches the claim by an inference step.
  - target: Apathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      Loss of serotonergic modulation is one of the two transmitter deficits the
      reviewed literature attributes apathy to. The source names dopamine
      alongside serotonin and states the relation as a belief rather than a
      demonstrated mechanism, so this edge carries the serotonergic arm only and
      resolves no intermediates.
    evidence:
    - reference: PMID:42646502
      reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: "apathy is thought to be related to losses of dopamine and serotonin"
      explanation: >
        Places apathy downstream of serotonergic loss. The quote is hedged
        ("thought to be related") and names dopamine in the same breath, so the
        claim follows by an inference step and this edge does not exclude a
        parallel dopaminergic route.
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Serotonin ↓ | Impairment and loss of serotonergic neurons within the raphe nuclei, which are responsible for modulating the limbic circuits and circadian rhythms. | Neuropsychiatric and vegetative symptoms: Depression, anxiety, sleep fragmentation, and sleep disturbances."
    explanation: >
      Establishes the node itself: raphe serotonergic neuron loss as a distinct
      non-dopaminergic mechanism in PD.
- name: Posterior Cortical and Limbic Atrophy
  biological_scale: TISSUE
  description: >
    Atrophy of posterior visual-association cortex together with limbic and
    thalamic structures accompanies the psychosis syndrome of Parkinson disease.
    It is the anatomical correlate the reviewed literature links hallucinations
    to, and is distinct from the nigrostriatal degeneration driving motor signs.
  locations:
  - preferred_term: precuneus
    term:
      id: UBERON:0006093
      label: precuneus cortex
  - preferred_term: occipital lobe
    term:
      id: UBERON:0002021
      label: occipital lobe
  - preferred_term: hippocampus
    term:
      id: UBERON:0002421
      label: hippocampal formation
  downstream:
  - target: Hallucinations
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      Hallucinations in PD psychosis are reported as linked to atrophy of
      visual-association, limbic and thalamic regions. The source states an
      anatomical association rather than a demonstrated causal sequence, and
      names no intermediate steps.
    evidence:
    - reference: PMID:42646502
      reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      quote_role: REVIEW_SYNTHESIS
      snippet: "Hallucinations in PD are linked to cortical atrophy in areas like the cuneus, precuneus, occipital gyrus, lingual and fusiform gyri, supramarginal and angular gyri, anterior cingulate, hippocampus, and thalamus."
      explanation: >
        Places the hallucination phenotype downstream of the atrophy this node
        describes. The quote asserts a link rather than causation, so the
        claim follows by an inference step.
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "Hallucinations in PD are linked to cortical atrophy in areas like the cuneus, precuneus, occipital gyrus, lingual and fusiform gyri, supramarginal and angular gyri, anterior cingulate, hippocampus, and thalamus."
    explanation: >
      Names atrophy in the posterior-cortical and limbic regions this node
      records and that its locations bind, which is the node's central
      assertion.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Abnormal brain connections lead to false perceptions."
    explanation: >
      The review's framing sentence for PD psychosis. It asserts a
      connectivity basis for false perceptions and names no anatomy, so it
      supports the node only as general context.
- name: Autophagy-Lysosome Pathway Dysfunction
  biological_scale: CELLULAR
  conforms_to: "disabled_macroautophagy#Failure of Cytoplasmic Quality Control"
  description: >
    Impairment of the autophagy-lysosome pathway disrupts clearance of misfolded
    proteins including alpha-synuclein. Multiple PD genes (GBA, LRRK2, VPS35,
    ATP13A2) regulate lysosomal function, and their mutations impair protein
    degradation capacity leading to toxic protein accumulation.
  genes:
  - preferred_term: GBA1
    term:
      id: hgnc:4177
      label: GBA
  - preferred_term: LRRK2
    term:
      id: hgnc:18618
      label: LRRK2
  - preferred_term: SNCA
    term:
      id: hgnc:11138
      label: SNCA
  - preferred_term: PRKN
    term:
      id: hgnc:8607
      label: PRKN
  - preferred_term: PINK1
    term:
      id: hgnc:14581
      label: PINK1
  - preferred_term: VPS35
    term:
      id: hgnc:13487
      label: VPS35
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: Autophagy
    term:
      id: GO:0006914
      label: autophagy
  - preferred_term: Chaperone-mediated Autophagy
    term:
      id: GO:0061684
      label: chaperone-mediated autophagy
  downstream:
  - target: Alpha-Synuclein Aggregation
    evidence:
    - reference: PMID:31761667
      reference_title: "Autophagy lysosomal pathway dysfunction in Parkinson's disease; evidence from human genetics."
      supports: SUPPORT
      snippet: "α-synuclein, encoded by the SNCA gene, is degraded mainly by the ALP, and mutations/multiplications in SNCA may lead to impairment of chaperone mediated autophagy or other ALP functions."
      explanation: This shows that autophagy-lysosome pathway dysfunction impairs α-synuclein clearance, supporting aggregation downstream.
  - target: Dopaminergic Neuron Loss
    evidence:
    - reference: PMID:31761667
      reference_title: "Autophagy lysosomal pathway dysfunction in Parkinson's disease; evidence from human genetics."
      supports: SUPPORT
      snippet: "In recent years, multiple lines of evidence from human genetic and molecular studies have highlighted the importance of the autophagy lysosomal pathway (ALP) in Parkinson's disease (PD)."
      explanation: This supports ALP dysfunction as a key PD mechanism contributing to neuronal degeneration.
  evidence:
  - reference: PMID:31761667
    reference_title: "Autophagy lysosomal pathway dysfunction in Parkinson's disease; evidence from human genetics."
    supports: SUPPORT
    snippet: "In recent years, multiple lines of evidence from human genetic and molecular studies have highlighted the importance of the autophagy lysosomal pathway (ALP) in Parkinson's disease (PD). Genes such as GBA and LRRK2, which harbor some of the most common mutations associated with PD, have essential roles in the ALP."
    explanation: This review establishes the genetic basis for autophagy-lysosome dysfunction in PD, identifying key genes and their mechanistic roles.
  - reference: PMID:31761667
    reference_title: "Autophagy lysosomal pathway dysfunction in Parkinson's disease; evidence from human genetics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Numerous other PD-related genes, such as PRKN, PINK1, TMEM175, SMPD1, CTSD, CTSB and many more, have also been reported to have important roles in the ALP."
    explanation: Supports binding PRKN and PINK1 to this node in addition to the mitochondrial node, since the same review places both in the autophagy-lysosome pathway.
  - reference: PMID:31761667
    reference_title: "Autophagy lysosomal pathway dysfunction in Parkinson's disease; evidence from human genetics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "mutations/multiplications in SNCA may lead to impairment of chaperone mediated autophagy or other ALP functions"
    explanation: Supports binding SNCA to this node, since SNCA variation is reported to impair chaperone-mediated autophagy, one of the two processes bound on the node.
  - reference: PMID:24819384
    reference_title: "Mutation in VPS35 associated with Parkinson's disease impairs WASH complex association and inhibits autophagy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Autophagy is impaired in cells expressing PD-mutant VPS35 or lacking WASH."
    explanation: Supports binding VPS35 to this node, by showing that the Parkinson-causing VPS35 allele impairs autophagy in cells.
  - reference: PMID:24819384
    reference_title: "Mutation in VPS35 associated with Parkinson's disease impairs WASH complex association and inhibits autophagy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The VPS35 D620N mutation causes a rare form of autosomal-dominant Parkinson's disease (PD). Here we show that this mutant associates poorly with the WASH complex and impairs WASH recruitment to endosomes."
    explanation: Gives the step at which the VPS35 allele acts, namely loss of WASH complex recruitment to endosomes upstream of the autophagy defect.
- name: LRRK2 GTPase Domain Dysregulation
  description: >
    Leucine-rich repeat kinase 2 (LRRK2) mutations disrupt the conformational dynamics of its ROC
    (Ras of complex proteins) G-domain, impairing GTPase activity and nucleotide (GTP/GDP) cycling.
    The arginine residue at position 1398 acts as a critical GTP-γ-phosphate sensor that regulates
    the ROC domain's active-to-inactive state transition. Pathogenic ROC/GTPase-domain mutations
    (e.g., R1441C/G/H) impair GTP hydrolysis, stabilize the constitutively active GTP-bound state,
    and enhance Rab29-dependent recruitment of LRRK2 to the trans-Golgi network. This dysregulation
    impairs vesicular trafficking, autophagosome-lysosome fusion, and clearance of alpha-synuclein
    aggregates, promoting neurodegeneration. Protective variants (e.g., R1398H) stabilize the
    GDP-bound inactive state and reduce disease risk, suggesting that GTPase domain normalization
    rather than kinase inhibition may be a disease-modifying therapeutic strategy.
  genes:
  - preferred_term: LRRK2
    term:
      id: hgnc:18618
      label: LRRK2
  cell_types:
  - preferred_term: Dopaminergic neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: Autophagy
    term:
      id: GO:0006914
      label: autophagy
    modifier: DECREASED
  - preferred_term: Intracellular protein localization
    term:
      id: GO:0008104
      label: intracellular protein localization
    modifier: DYSREGULATED
  - preferred_term: Vesicle-mediated transport
    term:
      id: GO:0016192
      label: vesicle-mediated transport
    modifier: DECREASED
  downstream:
  - target: Autophagy-Lysosome Pathway Dysfunction
    description: Dysregulated LRRK2 GTPase activity impairs Rab29-dependent autophagosome-lysosome fusion and alpha-synuclein clearance.
  - target: Dopaminergic Neuron Loss
    description: Impaired protein clearance and autophagy promote accumulation of toxic protein aggregates and neuronal death.
  evidence:
  - reference: PPR:PPR1263597
    reference_title: "R1398 is the GTP-𝛾-phosphate sensor that drives the ROC G-domain switching mechanism unique to Parkinson's disease-associated LRRK2"
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "A naturally occurring protective variant, R1398H, provides an alternative route for understanding how reduced disease risk may be achieved by tuning the regulatory GTPase domain rather than the kinase domain itself."
    explanation: Preprint demonstrates that GTPase domain tuning via protective R1398H variant may be a disease-modifying strategy, supporting the model that ROC domain conformational control is critical for LRRK2-related PD.
  - reference: PPR:PPR1263597
    reference_title: "R1398 is the GTP-𝛾-phosphate sensor that drives the ROC G-domain switching mechanism unique to Parkinson's disease-associated LRRK2"
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Purified ROC carrying R1398H is folded but resolves as a stable homodimer corresponding to the GDP-bound off state previously defined for wild-type ROC."
    explanation: Biochemical analysis demonstrates that the protective R1398H variant stabilizes the inactive GDP-bound state, providing structural evidence for GTPase domain regulation as a disease-modifying mechanism.
  - reference: PPR:PPR1263597
    reference_title: "R1398 is the GTP-𝛾-phosphate sensor that drives the ROC G-domain switching mechanism unique to Parkinson's disease-associated LRRK2"
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "R1398H reduces GTP hydrolysis, selectively weakens GTP-state stabilization while preserving GDP binding, and decreases Rab29-dependent trans-Golgi recruitment of full-length LRRK2."
    explanation: The protective variant reduces aberrant trans-Golgi recruitment, supporting the model that GTPase domain normalization may prevent pathological LRRK2 localization and consequent autophagy impairment.
- name: Gut Microbiome Dysbiosis
  conforms_to: "gut_dysbiosis#Age-Associated Gut Microbiota Alteration"
  description: >
    Parkinson disease cohorts show reproducible but modest gut microbiome
    shifts, including depletion of short-chain-fatty-acid-producing taxa and
    enrichment of genera linked to mucin or inflammatory biology. In the
    body-first model, dysbiosis is modeled as a plausible upstream trigger or
    modifier of intestinal inflammation and barrier dysfunction, not as an
    established direct cause of alpha-synuclein initiation.
  cell_types:
  - preferred_term: Enteroendocrine Cell
    term:
      id: CL:0000164
      label: enteroendocrine cell
  locations:
  - preferred_term: intestine
    term:
      id: UBERON:0000160
      label: intestine
  downstream:
  - target: Intestinal Inflammation and Barrier Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    description: >
      PD-associated dysbiosis may promote a pro-inflammatory intestinal state
      and barrier dysfunction, but the direction and necessity of this link
      remain unresolved in humans.
    evidence:
    - reference: PMID:33692356
      reference_title: "Meta-analysis of the Parkinson's disease gut microbiome suggests alterations linked to intestinal inflammation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This dysbiosis might result in a pro-inflammatory status which could be linked to the recurrent gastrointestinal symptoms affecting PD patients."
      explanation: >
        Cross-cohort microbiome meta-analysis supports a dysbiosis-to-inflammation
        interpretation but phrases the causal link as a possibility.
    - reference: PMID:34220443
      reference_title: "Serum and Fecal Markers of Intestinal Inflammation and Intestinal Barrier Permeability Are Elevated in Parkinson's Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A causal relationship has not been established, but gut dysbiosis is prevalent in PD and may lead to intestinal inflammation and barrier dysfunction."
      explanation: >
        Human marker data support modeling dysbiosis upstream of barrier and
        inflammatory changes while explicitly preserving causal uncertainty.
  evidence:
  - reference: PMID:33692356
    reference_title: "Meta-analysis of the Parkinson's disease gut microbiome suggests alterations linked to intestinal inflammation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found significant alterations in the PD-associated microbiome, which are robust to study-specific technical heterogeneities, although differences in microbiome structure between PD and controls are small."
    explanation: >
      Meta-analysis across ten 16S datasets supports a reproducible
      PD-associated gut microbiome signature, while noting small effect sizes.
  - reference: PMID:36332796
    reference_title: "Gut microbiome and Parkinson's disease: Perspective on pathogenesis and treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Alterations in the gut microbiome and associated metabolites may contribute to pathogenesis in PD."
    explanation: >
      Review-level evidence supports gut microbiome changes as plausible
      contributors to PD pathogenesis, but not as proven initiators.
- name: Intestinal Tight Junction Protein Loss
  biological_scale: MOLECULAR
  description: >
    Selective nigrostriatal dopaminergic injury depletes tight junction protein
    in the intestinal epithelium. In the 6-hydroxydopamine rat lesion model,
    zona occludens-1 falls in both ileum and colon and more markedly in the
    colon, while the enterocyte brush border is spared, making this a junctional
    lesion rather than generalized epithelial damage. The junctional loss is
    accompanied by rising circulating lipopolysaccharide and intestinal fatty
    acid-binding protein, the expected consequence of a leakier paracellular
    route. This node is where a brain-to-gut arm joins the body-first enteric
    chain curated elsewhere in this entry rather than running beside it. Its
    downstream target is the same barrier node the dysbiosis chain feeds, so the
    two directions converge and close a loop. Its human counterpart is only
    partly settled. Colonic biopsies from people with Parkinson disease show
    reduced occludin and disorganized staining of both junctional proteins,
    which agrees with the model, but no fall in zona occludens-1 by immunoblot
    and no measurable permeability change, which does not. That divergence is
    recorded as a HUMAN_MODEL_MISMATCH discussion rather than smoothed over here.
  cell_types:
  - preferred_term: intestinal epithelial cell
    term:
      id: CL:0002563
      label: intestinal epithelial cell
  biological_processes:
  - preferred_term: tight junction organization
    term:
      id: GO:0120193
      label: tight junction organization
    modifier: DECREASED
  cellular_components:
  - preferred_term: bicellular tight junction
    term:
      id: GO:0005923
      label: bicellular tight junction
    modifier: DECREASED
  locations:
  - preferred_term: colon
    term:
      id: UBERON:0001155
      label: colon
  - preferred_term: ileum
    term:
      id: UBERON:0002116
      label: ileum
  downstream:
  - target: Intestinal Inflammation and Barrier Dysfunction
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >
      Depletion of tight junction protein raises paracellular permeability and
      permits translocation of luminal microbial product, measurable as rising
      circulating lipopolysaccharide and intestinal fatty acid-binding protein.
      The step to the barrier half of the target node is direct; the step to its
      inflammatory half runs through that translocation and the immune
      activation it provokes, which is why the link is recorded with known
      intermediates rather than as direct.
    evidence:
    - reference: PMID:42732868
      reference_title: "Striatal 6-hydroxydopamine lesion in rats induces dysregulation of the gut barrier."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "6-OHDA lesioning led to increased circulating lipopolysaccharide (LPS) and intestinal fatty acid-binding protein (iFABP), consistent with impaired gut barrier function."
      explanation: >
        Measures the translocation readouts in the same animals in which the
        junctional protein was depleted, supporting the step from tight junction
        loss to a functionally leaky barrier.
  evidence:
  - reference: PMID:42732868
    reference_title: "Striatal 6-hydroxydopamine lesion in rats induces dysregulation of the gut barrier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "the tight junction protein zona occludens-1 (ZO-1) had marked reductions in both the ileum and more profoundly in the colon, indicating regional vulnerability"
    explanation: >
      Establishes the node itself and its regional gradient, with the colon more
      affected than the ileum.
  - reference: PMID:42732868
    reference_title: "Striatal 6-hydroxydopamine lesion in rats induces dysregulation of the gut barrier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Immunostaining for Villin, an actin-binding protein in microvilli, revealed no changes to the enterocyte brush border in either the ileum or colon."
    explanation: >
      A negative result that narrows the node. The brush border is intact, so
      the lesion is specific to the junctional compartment rather than reflecting
      broad enterocyte injury.
  - reference: PMID:37271045
    reference_title: "Nigrostriatal 6-hydroxydopamine lesions increase alpha-synuclein levels and permeability in rat colon."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "6-OHDA decreased the Zonula occludens protein 1 barrier integrity score, suggesting increased colonic permeability."
    explanation: >
      Independent replication of the same junctional protein deficit after
      nigrostriatal lesioning, reported by a different group in a separate study.
- name: Intestinal Inflammation and Barrier Dysfunction
  conforms_to: "gut_dysbiosis#Intestinal Barrier Dysfunction and Microbial Translocation"
  description: >
    Sporadic Parkinson disease is associated with elevated intestinal
    inflammatory and permeability markers. These changes may create a local
    milieu that increases alpha-synuclein expression or exposes enteric neurons
    to amyloidogenic microbial or dietary compounds, but whether they initiate
    body-first PD or arise secondary to gut autonomic dysfunction remains open.
  biological_processes:
  - preferred_term: Inflammatory Response
    term:
      id: GO:0006954
      label: inflammatory response
  downstream:
  - target: Enteric Alpha-Synuclein Seeding
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    description: >
      Local gut inflammation and barrier leakiness may increase enteric
      alpha-synuclein expression or amyloidogenic exposure, providing a
      permissive setting for enteric alpha-synuclein seeding.
    evidence:
    - reference: PMID:34220443
      reference_title: "Serum and Fecal Markers of Intestinal Inflammation and Intestinal Barrier Permeability Are Elevated in Parkinson's Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Gut dysbiosis is common in PD and can result in local inflammatory changes and barrier dysfunction/disruption, which may increase alpha-synuclein expression and facilitate its exposure to amyloidogenic compounds found in the gut, thus possibly contributing to key pathogenic events in PD; prospective evidence is nevertheless scarce"
      explanation: >
        Human marker study discussion supports a plausible route from
        dysbiosis/inflammation/barrier disruption to enteric alpha-synuclein
        seeding but explicitly notes scarce prospective evidence.
    - reference: PMID:42295088
      reference_title: "Peripheral Immune Challenge Drives Enteric α-Synuclein and Tau Pathology in LRRK2 G2019S Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Overall, our findings demonstrate that chronic peripheral inflammation synergizes with LRRK2 G2019S to trigger early intestinal inflammation and α-synuclein/tau co-pathology in the absence of overt neurodegeneration."
      explanation: >-
        Supplies the missing directionality for this edge in a model system:
        chronic low-dose LPS exposure produces colonic immune infiltration and
        then enteric alpha-synuclein accumulation and phosphorylation. The
        effect is conditional on the LRRK2 G2019S genotype, so it does not show
        that inflammation alone seeds enteric alpha-synuclein in sporadic human
        disease.
    - reference: PMID:42327194
      reference_title: "Gut bacterial Infection drives Parkinsonian pathology in LRRK2 G2019S Knock-in Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In parallel, recurrent infection induced pronounced intestinal p-αSyn accumulation and expansion of pathology beyond the epithelial layer in KI mice, supporting a gut-brain axis mechanism linking intestinal inflammation to neurodegeneration."
      explanation: >-
        Independent inflammatory trigger, same edge: recurrent Citrobacter
        rodentium infection drives colonic inflammation and barrier dysfunction
        followed by intestinal phosphorylated alpha-synuclein accumulation.
        Again genotype-conditional - wild-type mice were largely resistant - so
        it supports a gene-environment route into enteric seeding rather than a
        general one.
  evidence:
  - reference: PMID:34220443
    reference_title: "Serum and Fecal Markers of Intestinal Inflammation and Intestinal Barrier Permeability Are Elevated in Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Calprotectin and zonulin are markers of intestinal inflammation and barrier permeability, respectively."
    explanation: >
      Establishes the measured marker interpretation for this intestinal
      inflammation and barrier dysfunction node.
  - reference: PMID:34220443
    reference_title: "Serum and Fecal Markers of Intestinal Inflammation and Intestinal Barrier Permeability Are Elevated in Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mean calprotectin was higher in PD, both in serum (14.26 mcg/ml ± 4.50 vs. 5.94 mcg/ml ± 3.80, p = 0.0125) and stool (164.54 mcg/g ± 54.19 vs. 56.19 mcg/g ± 35.88, p = 0.0048)."
    explanation: >
      Case-control data support elevated intestinal inflammatory markers in PD.
- name: Enteric Alpha-Synuclein Seeding
  description: >
    In the body-first model, misfolded alpha-synuclein appears first in enteric
    or peripheral autonomic neural tissue and serves as the initiating seed for
    subsequent gut-to-brain spread. Direct causal support comes primarily from
    animal models that seed pathologic alpha-synuclein in the gastrointestinal
    wall.
  cell_types:
  - preferred_term: Enteric Neuron
    term:
      id: CL:0007011
      label: enteric neuron
  locations:
  - preferred_term: enteric nervous system
    term:
      id: UBERON:0002005
      label: enteric nervous system
  biological_processes:
  - preferred_term: inclusion body assembly
    term:
      id: GO:0070841
      label: inclusion body assembly
  downstream:
  - target: Vagal-Brainstem Alpha-Synuclein Propagation
    causal_link_type: DIRECT
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    description: >
      Enteric alpha-synuclein seeds can propagate first to vagal brainstem
      nuclei and then to additional brain regions.
    evidence:
    - reference: PMID:31255487
      reference_title: "Transneuronal Propagation of Pathologic α-Synuclein from the Gut to the Brain Models Parkinson's Disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Spread of pathologic α-syn in brain, as assessed by phosphorylation of serine 129 of α-syn, was observed first in the dorsal motor nucleus, then in caudal portions of the hindbrain"
      explanation: >
        Gut-seeded mouse alpha-synuclein pathology first appears in vagal
        brainstem regions, supporting the enteric seeding to vagal propagation
        edge.
    - reference: PMID:39241780
      reference_title: "Gut-induced alpha-Synuclein and Tau propagation initiate Parkinson's and Alzheimer's disease co-pathology and behavior impairments."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Gut pathology was initially observed, and α-Syn or Tau pathology was subsequently propagated into the DMV or NTS and then to other brain regions."
      explanation: >
        Independent gut-inducible mouse models support propagation from gut
        pathology to vagal brainstem nuclei and then broader brain regions.
  - target: Constipation
    causal_link_type: UNKNOWN
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    description: >
      Enteric or autonomic involvement is a plausible contributor to early
      constipation in body-first PD, but this edge remains clinically inferred.
    evidence:
    - reference: PMID:34220443
      reference_title: "Serum and Fecal Markers of Intestinal Inflammation and Intestinal Barrier Permeability Are Elevated in Parkinson's Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "most people with sporadic PD develop gastrointestinal symptoms related to decreased transit time, constipation preceding the motor dysfunction with more than a decade in some cases"
      explanation: >
        Supports constipation as an early gastrointestinal manifestation
        compatible with body-first PD, without proving enteric seeding as its
        cause.
  evidence:
  - reference: PMID:31255487
    reference_title: "Transneuronal Propagation of Pathologic α-Synuclein from the Gut to the Brain Models Parkinson's Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "fibrils were injected into the duodenal and pyloric muscularis layer"
    explanation: >
      The gut-to-brain transmission model experimentally seeds pathologic
      alpha-synuclein in the gastrointestinal wall.
  - reference: PMID:34220443
    reference_title: "Serum and Fecal Markers of Intestinal Inflammation and Intestinal Barrier Permeability Are Elevated in Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The coexistence of an amyloidogenic gut microbiota with intestinal inflammation (leading to local overexpression of alpha-synuclein) and altered intestinal barrier permeability (exposing alpha-synuclein to the amyloidogenic xenobiotics) may play a key role in triggering the initial alpha-synuclein conformational changes in some people with sporadic PD"
    explanation: >
      Human review/discussion within the marker study supports enteric
      alpha-synuclein seeding as a plausible but not proven event in some
      sporadic PD cases.
- name: Vagal-Brainstem Alpha-Synuclein Propagation
  description: >
    Pathologic alpha-synuclein seeded in the gastrointestinal wall can propagate
    through vagal connections to the dorsal motor nucleus, nucleus tractus
    solitarius, caudal hindbrain, and ultimately midbrain and forebrain regions.
    Vagotomy experiments provide the strongest causal evidence for this
    body-first conduit.
  locations:
  - preferred_term: vagus nerve
    term:
      id: UBERON:0001759
      label: vagus nerve
  - preferred_term: midbrain
    term:
      id: UBERON:0001891
      label: midbrain
  downstream:
  - target: Alpha-Synuclein Aggregation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    intermediate_mechanisms:
    - dorsal motor nucleus and nucleus tractus solitarius involvement
    - caudal hindbrain and higher brain region propagation
    description: >
      Vagal-brainstem propagation links gut-origin pathology to the broader
      central alpha-synuclein aggregation cascade.
    evidence:
    - reference: PMID:31255487
      reference_title: "Transneuronal Propagation of Pathologic α-Synuclein from the Gut to the Brain Models Parkinson's Disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Truncal vagotomy and α-syn deficiency prevented the gut-to-brain spread of α-synucleinopathy and associated neurodegeneration and behavioral deficits."
      explanation: >
        Vagotomy rescue supports the vagus nerve as a required conduit for
        gut-origin alpha-synucleinopathy reaching the brain.
    - reference: PMID:39241780
      reference_title: "Gut-induced alpha-Synuclein and Tau propagation initiate Parkinson's and Alzheimer's disease co-pathology and behavior impairments."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Truncal vagotomy and α-Syn deficiency significantly inhibited synucleinopathy or tauopathy spreading."
      explanation: >
        Independent gut-inducible mouse data support the same vagal conduit for
        inhibitable synucleinopathy spread.
  - target: Pontine Tegmental Alpha-Synuclein Pathology
    causal_link_type: DIRECT
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    description: >
      As vagal-brainstem propagation continues rostrally, the pontine tegmentum
      - the site of the REM-atonia-generating circuit - is reached ahead of the
      nigrostriatal and cortical structures that define overt motor and
      cognitive disease.
    evidence:
    - reference: PMID:20187227
      reference_title: "Evidence in favor of Braak staging of Parkinson's disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "involvement of anterior olfactory nucleus, medulla, and pontine tegmentum occur earlier"
      explanation: >
        A large autopsy series confirms pontine tegmental Lewy pathology
        precedes substantia nigra involvement in the Braak sequence, the
        anatomical basis for this node sitting upstream of the nigrostriatal
        nodes in the pathograph.
  evidence:
  - reference: PMID:31255487
    reference_title: "Transneuronal Propagation of Pathologic α-Synuclein from the Gut to the Brain Models Parkinson's Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Analysis of human pathology led Braak to postulate that α-synuclein (α-syn) pathology could spread from the gut to brain via the vagus nerve."
    explanation: >
      Establishes the gut-to-brain vagal propagation hypothesis tested by the
      mouse transmission model.
  - reference: PMID:39241780
    reference_title: "Gut-induced alpha-Synuclein and Tau propagation initiate Parkinson's and Alzheimer's disease co-pathology and behavior impairments."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "α-Syn and Tau co-pathology can propagate from the gut to the brain, triggering behavioral disorders."
    explanation: >
      Supports gut-to-brain propagation in a gut-inducible transgenic mouse
      system.
- name: Pontine Tegmental Alpha-Synuclein Pathology
  description: >
    Braak staging places pontine tegmental involvement ahead of substantia
    nigra pathology in the same caudo-rostral progression that vagal-brainstem
    propagation follows. The pontine tegmentum houses the glutamatergic REM-on
    circuit whose descending limb generates REM sleep muscle atonia. In
    Parkinson disease the lesion at this site is degenerative rather than
    structural, narcoleptic, or drug-induced, and it arrives at a topographic
    stage that precedes the nigrostriatal degeneration defining overt motor
    disease.
  role: trigger
  biological_scale: CELLULAR
  conforms_to: "rem_sleep_atonia_control_failure#Lesion of the Pontine REM-Atonia Generator"
  biological_processes:
  - preferred_term: inclusion body assembly
    term:
      id: GO:0070841
      label: inclusion body assembly
  cell_types:
  - preferred_term: glutamatergic REM-on neuron of the sublaterodorsal nucleus
    term:
      id: CL:0000540
      label: neuron
    modifier: DECREASED
  locations:
  - preferred_term: sublaterodorsal nucleus
    term:
      id: UBERON:8440035
      label: sublaterodorsal nucleus
  - preferred_term: pons
    term:
      id: UBERON:0000988
      label: pons
  - preferred_term: brainstem
    term:
      id: UBERON:0002298
      label: brainstem
  downstream:
  - target: Loss of Descending Drive to Inhibitory Premotor Neurons
    causal_link_type: DIRECT
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    description: >
      Pathology involving the pontine REM-on glutamatergic population removes
      the excitatory drive its descending axons carry to medullary and spinal
      inhibitory premotor neurons.
  evidence:
  - reference: PMID:20187227
    reference_title: "Evidence in favor of Braak staging of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The proportion of cases that fit the PD staging scheme was 67% for incidental LBs; 86% for PSP with LBs; 86% for pure LBD; and 84% for LBD with AD"
    explanation: >
      Dickson's own autopsy series, rather than its statement of what Braak
      proposed: the caudo-rostral ordering that places pontine tegmental
      involvement before substantia nigra pathology holds in 84-86% of Lewy
      body disease cases. This is what licenses placing this node upstream of
      the nigrostriatal nodes in the pathograph.
  - reference: PMID:17412731
    reference_title: "Pathophysiology of REM sleep behaviour disorder and relevance to neurodegenerative disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The hypothesized pathophysiology of RBD is presented in relation to the Braak staging system for Parkinson's disease, in which the topography and temporal sequence of synuclein pathology in the brain could explain the evolution of parkinsonism and/or dementia well after the onset of RBD."
    explanation: >
      Ties the Braak sequence specifically to RBD pathophysiology rather than
      to brainstem involvement in general, which is the step that licenses
      placing this node upstream of the atonia nodes and that the staging paper
      alone does not make. Graded OTHER rather than HUMAN_CLINICAL because the
      quoted sentence states a hypothesis this Brain review advances, not a
      patient observation it reports - matching the grade
      `rem_sleep_atonia_control_failure.yaml` gives the comparable "is proposed
      as" sentence from the same paper.
  - reference: PMID:39577924
    reference_title: "Post-mortem neuropathology of idiopathic rapid eye movement sleep behaviour disorder: a case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In all participants, α-synuclein was found in the structures that regulate REM sleep atonia (eg, subcoeruleus nucleus, gigantocellular reticular nucleus, laterodorsal tegmentum, and amygdala)"
    explanation: >
      Places the pathology in the atonia-generating nuclei themselves, not
      merely somewhere in the pontine tegmentum. The pontine tegmentum is a
      large region and Braak stage 2 is classically locus coeruleus and caudal
      raphe, so without this the lesion claim would rest on the region-level
      ordering alone. Note the inferential step: this cohort is isolated RBD
      rather than diagnosed Parkinson disease, so it evidences the lesion
      topography rather than its presence in established PD.

- name: Loss of Descending Drive to Inhibitory Premotor Neurons
  description: >
    REM atonia is actively imposed rather than passively permitted: the
    glutamatergic REM-on population excites glycinergic and GABAergic premotor
    neurons in the ventromedial medulla and spinal cord, which hyperpolarise
    skeletal motor neurons. Losing the descending drive therefore releases
    motor neurons from an inhibition that should be present. This descending
    pathway is separate from the ascending pathway that generates the EEG
    features of REM sleep, so it can be lost while REM sleep itself proceeds
    normally - which is what polysomnography shows in Parkinson disease.
  role: amplifier
  biological_scale: CELLULAR
  conforms_to: "rem_sleep_atonia_control_failure#Loss of Descending Glutamatergic Drive to Inhibitory Premotor Neurons"
  biological_processes:
  - preferred_term: glutamatergic synaptic transmission
    term:
      id: GO:0035249
      label: synaptic transmission, glutamatergic
    modifier: DECREASED
  - preferred_term: inhibitory regulation of skeletal motor neuron output
    term:
      id: GO:0006937
      label: regulation of muscle contraction
    modifier: DECREASED
  locations:
  - preferred_term: brainstem
    term:
      id: UBERON:0002298
      label: brainstem
  downstream:
  - target: REM Sleep Muscle Atonia Loss
    causal_link_type: DIRECT
    hypothesis_groups:
    - body_first_enteric_alpha_synuclein_model
    description: >
      Without descending excitation of the inhibitory premotor pool, skeletal
      motor neurons are not hyperpolarised during REM sleep and muscle tone
      persists.
  evidence:
  - reference: PMID:17884926
    reference_title: "The pontine REM switch: past and present."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In the REM-on area are two populations of glutamatergic neurons, the
      first of which projects to the basal forebrain and regulates EEG
      components of REM sleep and the second of which projects to the
      ventromedial medulla and spinal cord and regulates atonia during REM
      sleep.
    explanation: >
      The two-population anatomy this node depends on: a descending atonia
      limb separable from the ascending EEG limb.
  - reference: PMID:17884926
    reference_title: "The pontine REM switch: past and present."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Our findings demonstrating independent pathways mediating atonia and
      the EEG components of REM provide a basis for their occasional
      dissociation in pathological states, e.g. REM sleep behaviour
      disorder.
    explanation: >
      States the dissociation explicitly and names RBD as its pathological
      instance, which is what permits atonia to fail here while REM sleep
      itself is preserved.

- name: REM Sleep Muscle Atonia Loss
  description: >
    Excess tonic or phasic electromyographic activity during scored REM sleep,
    the measurable abnormality that underlies dream enactment in Parkinson
    disease. Polysomnography confirms REM sleep
    without atonia in the majority of PD patients studied - more often than
    the clinical behavioural history alone identifies - so the
    electrophysiological finding runs ahead of, and is more sensitive than, a
    clinical diagnosis of REM sleep behavior disorder.
  role: central_effector
  biological_scale: ORGANISM
  conforms_to: "rem_sleep_atonia_control_failure#Failure of REM Sleep Skeletal Muscle Atonia"
  biological_processes:
  - preferred_term: REM sleep
    term:
      id: GO:0042747
      label: circadian sleep/wake cycle, REM sleep
    modifier: ABNORMAL
  - preferred_term: skeletal muscle contraction during REM sleep
    term:
      id: GO:0003009
      label: skeletal muscle contraction
    modifier: INCREASED
  downstream:
  - target: REM Sleep Behavior Disorder
    causal_link_type: DIRECT
    description: >
      Where atonia loss is accompanied by dream-enactment behaviour rather than
      remaining electrophysiologically silent, the released motor programmes
      generated during dreaming are enacted, producing the clinical phenotype.
    evidence:
    - reference: PMID:12196654
      reference_title: "REM sleep behavior disorder and REM sleep without atonia in Parkinson's disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Of these 19 patients with PD, 8 (42%) did not present with behavioral manifestations of RBD, and their cases may represent preclinical forms of RBD associated with PD."
      explanation: >
        Supports the conditional form this edge is written in rather than an
        unrestricted claim: 42% of PD patients with polysomnographic atonia
        loss have no behavioural enactment, so atonia loss is necessary but
        not sufficient for the clinical phenotype, and the two findings stay
        separable.
  evidence:
  - reference: PMID:12196654
    reference_title: "REM sleep behavior disorder and REM sleep without atonia in Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nineteen (58%) of 33 patients with PD but only 1 of 16 control subjects had REM sleep without atonia."
    explanation: >
      Direct polysomnographic quantification of REM sleep without atonia in a
      PD cohort versus controls - the measurement this node's conformance
      claim requires.
  - reference: PMID:12196654
    reference_title: "REM sleep behavior disorder and REM sleep without atonia in Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One third of patients with PD met the diagnostic criteria of RBD based on PSG recordings."
    explanation: >
      Shows the polysomnographic finding is more prevalent than, and only
      partly overlaps with, a clinical RBD diagnosis - consistent with the
      module's requirement that the electrophysiological finding, not the
      behavioural history, is what satisfies conformance at this node.
  - reference: PMID:21832215
    reference_title: "Associated factors for REM sleep behavior disorder in Parkinson disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      An unselected cohort of sleep-disturbed patients with PD (n=457) was
      investigated with video-supported polysomnography.
    explanation: >
      Establishes the measurement method and scale behind the frequency below:
      video-supported polysomnography in an unselected PD cohort, an order of
      magnitude larger than the 33-patient series the rest of this node rests
      on.
  - reference: PMID:21832215
    reference_title: "Associated factors for REM sleep behavior disorder in Parkinson disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The overall frequency of RBD was 46%."
    explanation: >
      Corroborates at roughly fourteen times the cohort size that the finding
      is common in unselected PD. Sixel-Doring et al. report video-PSG-confirmed
      RBD by their own modified definition rather than REM sleep without
      atonia, so the 46% figure is the counterpart of the smaller series'
      one-third PSG-diagnosed-RBD figure rather than of its 58% atonia-loss
      figure; both series place the finding in the same range and neither
      contradicts the other. The atonia-loss measurement this node's
      conformance claim rests on remains the 58% figure above.
- name: Central Alpha-Synuclein Initiation
  description: >
    In the brain-first model, the initial alpha-synuclein pathology begins in
    central sites such as the olfactory bulb or amygdala, then spreads through
    connected brain regions and later to peripheral autonomic structures. This
    node captures the competing central-origin route without asserting that it
    applies to all Parkinson disease.
  locations:
  - preferred_term: olfactory bulb
    term:
      id: UBERON:0002264
      label: olfactory bulb
  - preferred_term: amygdala
    term:
      id: UBERON:0001876
      label: amygdala
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: inclusion body assembly
    term:
      id: GO:0070841
      label: inclusion body assembly
  downstream:
  - target: Alpha-Synuclein Aggregation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - brain_first_central_alpha_synuclein_model
    intermediate_mechanisms:
    - central network propagation from olfactory bulb or amygdala
    description: >
      Central initiation feeds into the broader alpha-synuclein aggregation and
      propagation cascade through connected brain networks.
    evidence:
    - reference: PMID:38519273
      reference_title: "Brain-first vs. body-first Parkinson's disease: An update on recent evidence."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the initial pathology starts either in the olfactory bulb or amygdala leading to a brain-first subtype, or in the enteric nervous system leading to a body-first subtype."
      explanation: >
        Human subtype review supports olfactory bulb or amygdala origin as the
        central initiation route for the brain-first model.
  evidence:
  - reference: PMID:38519273
    reference_title: "Brain-first vs. body-first Parkinson's disease: An update on recent evidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Molecular imaging studies were generally in agreement with the model, whereas structural imaging studies, such as MRI volumetry, showed conflicting findings."
    explanation: >
      Review-level synthesis supports the brain-first/body-first model while
      noting that not all imaging modalities agree.
  - reference: PMID:32830221
    reference_title: "Brain-first versus body-first Parkinson's disease: a multimodal imaging case-control study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the PDRBD- data were compatible with a brain-first trajectory, characterized by primary loss of putaminal FDOPA uptake followed by a secondary loss of cardiac MIBG signal and 11C-donepezil signal."
    explanation: >
      Primary PET, MIBG, MRI, and gut-transit imaging evidence supports the
      central-first route by identifying a de novo PD subgroup with primary
      putaminal dopaminergic dysfunction followed by peripheral autonomic loss.
  - reference: PMID:40209563
    reference_title: "Amygdala neurodegeneration differentiates brain-first and body-first Parkinson's disease: An MRI study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'The degeneration of amygdala is distinctively pronounced in "brain-first" Parkinson''s disease, supporting differential disease progression patterns between subtypes.'
    explanation: >-
      Diffusion microstructure MRI gives the amygdala half of this node a
      human in vivo correlate: amygdala free interstitial fluid is higher in the
      brain-first group, matching the amygdala as a candidate central initiation
      site.
  - reference: PMID:40209563
    reference_title: "Amygdala neurodegeneration differentiates brain-first and body-first Parkinson's disease: An MRI study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "subtypes based on REM sleep behavior disorder history. Microstructural integrity was assessed using diffusion microstructure MRI."
    explanation: >-
      Bounds that result. The study is a retrospective cross-sectional analysis
      of 30 patients whose subtype labels come from REM-sleep-behavior-disorder
      history rather than from an observed origin site, so it supports an
      amygdala-differentiating pattern rather than amygdala initiation.
  - reference: PMID:33547846
    reference_title: "α-Synuclein Spread from Olfactory Bulb Causes Hyposmia, Anxiety, and Memory Loss in BAC-SNCA Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Severe α-Syn pathology in the transgenic mice injected with α-Syn preformed fibrils was initially observed along the olfactory pathway and later in the brain regions that are included in the limbic system and have connections with it."
    explanation: >-
      Rodent counterpart to the marmoset olfactory-bulb seeding result: an
      alpha-synuclein seed placed in the olfactory bulb spreads first along the
      olfactory pathway and then into connected limbic regions, supporting the
      anatomical possibility of the centrifugal route from a central site.
  - reference: PMID:33547846
    reference_title: "α-Synuclein Spread from Olfactory Bulb Causes Hyposmia, Anxiety, and Memory Loss in BAC-SNCA Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Behavioral analyses revealed hyposmia, followed by anxiety-like behavior and memory impairment, but not motor dysfunction, depression-like behavior, or circadian rhythm disturbance."
    explanation: >-
      Qualifies that model. Spread required an imposed preformed-fibril seed in
      mice overexpressing human SNCA, and produced no motor dysfunction, so it
      establishes anatomical possibility of olfactory-to-limbic propagation
      rather than spontaneous central initiation of a parkinsonian syndrome.
- name: Nigral Cellular Senescence
  conforms_to:
  - "cellular_senescence#Senescent Cell Accumulation"
  - "cellular_senescence#Senescence-Associated Secretory Phenotype"
  biological_scale: CELLULAR
  description: >-
    Cells bearing senescence markers accumulate in the substantia nigra in Parkinson disease, in
    astrocytes and in the dopaminergic neurons themselves. Post-mortem nigral tissue carries raised
    p21, reduced nuclear lamin B1 and HMGB1, and the secreted factors of a
    senescence-associated secretory phenotype, among them IL-6, IL-1alpha, IL-8 and MMP-3. In
    dopaminergic neurons the transcriptional regulator SATB1 represses p21, so reduced SATB1
    activity is the proposed route into a p21-dependent arrest in these post-mitotic cells. In
    mouse models the herbicide paraquat and alpha-synuclein preformed fibrils each induce glial
    senescence, and depleting senescent cells protects against paraquat-induced loss of nigral
    dopaminergic neurons.
  notes: >-
    The human evidence is post-mortem marker measurement, which cannot order senescence and
    degeneration in time; the causal edges below rest on mouse models. The markers do not agree
    across studies. PMID:29386135 reports p16INK4a elevated in parkinsonian substantia nigra pars
    compacta, while PMID:34359864 finds p16 unchanged in human PD midbrain and the p21, lamin B1
    and HMGB1 changes present. p21 is the one marker raised in both human datasets, so it carries
    the node; p16 is recorded as contested rather than as a feature of the node, and no p16 or
    CDKN2A term is bound.

    Both astrocytes and dopaminergic neurons are bound because the two human studies implicate
    different cells: PMID:29386135 localises the marker loss to GFAP-positive astrocytes and
    reports no difference in neighbouring non-astrocytic cells, while PMID:31543366 and
    PMID:34359864 find raised p21 within tyrosine-hydroxylase-positive neurons. Microglia are not
    bound, because the only PD evidence for microglial senescence here is the mouse
    preformed-fibril model, not human tissue.
  cell_types:
  - preferred_term: Astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: cellular senescence
    term:
      id: GO:0090398
      label: cellular senescence
    modifier: INCREASED
  downstream:
  - target: Neuroinflammation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Route from the senescent nigral population to the neuroinflammation node: the senescent cells
      in parkinsonian substantia nigra carry a secretory phenotype whose measured components are
      cytokines the neuroinflammation node already holds. Which secreted factor reaches which glial
      population is not resolved, and one candidate was tested and found insufficient on its own.
    evidence:
    - reference: PMID:29386135
      reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "Compared to control tissues, Parkinsonian SNpc tissues displayed elevated expression of the senescence marker p16INK4a, and several SASP factors included the protease MMP-3 and the pro-inflammatory cytokines interleukin-6 (IL-6), IL-1α, and IL-8"
      explanation: >-
        Parkinsonian nigral tissue carries both a senescence marker and secreted inflammatory
        factors, which is the measurement behind this edge. It is a cross-sectional association in
        post-mortem tissue, so it does not establish that the senescent cells are the source of
        the inflammatory state.
  - target: Dopaminergic Neuron Loss
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Senescent cells contribute to nigral dopaminergic loss rather than only marking it. The
      evidence is interventional but entirely from the paraquat mouse model, where genetically
      depleting senescent cells preserves the dopaminergic marker that the exposure otherwise
      reduces. No human or alpha-synuclein-driven equivalent of the depletion experiment is
      recorded here.
    evidence:
    - reference: PMID:29386135
      reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
      supports: SUPPORT
      directness: DIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "In the mouse SNpc, PQ caused a significant decline in a marker of DAergic neurons, tyrosine hydroxylase (TH); co-administration of GCV with PQ prevented this decline"
      explanation: >-
        In p16-3MR mice, clearing senescent cells prevents the paraquat-induced fall in nigral
        tyrosine hydroxylase. This is the one experiment making senescence causal for dopaminergic
        loss rather than correlated with it, and it is in a toxicant model.
    - reference: PMID:29386135
      reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Significantly, inducible depletion of in vivo senescence reduces the development of neurodegenerative phenotypes associated with systemic PQ exposure, demonstrating that senescent cells contribute to neurodegeneration in an in vivo neurodegenerative disease model."
      explanation: >-
        The authors' summary of the depletion result across their neurodegenerative readouts, which
        extends the tyrosine hydroxylase measurement above to the broader phenotype. Indirect
        because the claim is about neurodegenerative phenotypes generally rather than nigral
        neuron counts.
    - reference: PMID:29386135
      reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: IN_VITRO
      snippet: "but IL-6 alone was not sufficient to induce significant degeneration of cultured DAergic neurons, suggesting that additional SASP factors may be required"
      explanation: >-
        The authors' test of the single best-measured secreted factor, and the reason this edge
        carries unknown intermediates: IL-6 does not kill cultured dopaminergic neurons on its own,
        so which secreted factor mediates the loss is unresolved. Supports the edge only indirectly,
        since it establishes what the route is not.
  evidence:
  - reference: PMID:29386135
    reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we demonstrate that senescent cell markers are preferentially present within astrocytes in PD brain tissues."
    explanation: >-
      The human observation behind the astrocyte binding on this node: senescence markers in PD
      brain tissue sit preferentially in astrocytes.
  - reference: PMID:29386135
    reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Astrocytes (GFAP+ cells) were found to be lamin B1 deficient in PD SNpc tissues while no significant difference was detected in PD versus aged-matched control tissues in non-astrocytic (GFAP−) neighboring cells"
    explanation: >-
      Locates the lamin B1 loss in nigral astrocytes specifically, with the neighbouring
      non-astrocytic cells as the internal comparison. This is why the node names astrocytes rather
      than nigral tissue as a whole.
  - reference: PMID:34359864
    reference_title: "Alpha-Synuclein Preformed Fibrils Induce Cellular Senescence in Parkinson's Disease Models."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our WB analysis revealed that the levels of Lamin B1 (Figure 7A,B), HMGB1 (Figure 7A,C) and SATB1 (Figure 7A,D) were substantially reduced, whereas the p21 level was significantly increased (Figure 7A,F) in the midbrain of human PD postmortem tissues compared to age- and gender-matched controls."
    explanation: >-
      Independent human measurement of the marker set in PD midbrain, in eight cases against eight
      matched controls. It supports the lamin B1, HMGB1 and p21 changes this node describes, and
      reports reduced SATB1 protein, which is the link to the SATB1 mechanism.
  - reference: PMID:34359864
    reference_title: "Alpha-Synuclein Preformed Fibrils Induce Cellular Senescence in Parkinson's Disease Models."
    supports: REFUTE
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, p16 levels were not significantly changed in the midbrain of human PD postmortems (Figure 7A,E)."
    explanation: >-
      Contradicts the elevated p16INK4a reported in parkinsonian nigra by PMID:29386135. Recorded
      against the node because p16 is one of the markers a senescence claim normally rests on, and
      the two human datasets disagree on it. This is the reason the node binds no p16 term.
  - reference: PMID:31543366
    reference_title: Loss of SATB1 Induces p21-Dependent Cellular Senescence in Post-mitotic Dopaminergic Neurons.
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Crucially, we found a significant increase in the intensity of p21 staining within TH+ DA neurons in PD patient brain slices compared to age-matched controls"
    explanation: >-
      Puts the raised p21 inside tyrosine-hydroxylase-positive nigral neurons in sporadic PD, which
      is the basis for binding the dopaminergic neuron cell type here as well as the astrocyte.
  - reference: PMID:31543366
    reference_title: Loss of SATB1 Induces p21-Dependent Cellular Senescence in Post-mitotic Dopaminergic Neurons.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: IN_VITRO
    snippet: "Here we show that the genetic ablation of SATB1 induces a senescence phenotype in hESC derived DA neurons."
    explanation: >-
      The mechanism this node attributes to SATB1, in the system the authors show it in: deleting
      SATB1 is sufficient for a senescence phenotype in human stem-cell-derived dopaminergic
      neurons. Indirect because sufficiency in a cell model does not establish that this is what
      drives senescence in patients.
  - reference: PMID:31543366
    reference_title: Loss of SATB1 Induces p21-Dependent Cellular Senescence in Post-mitotic Dopaminergic Neurons.
    supports: SUPPORT
    directness: DIRECT
    evidence_source: IN_VITRO
    snippet: "Moreover, inhibition of CDKN1A in SATB1KO DA neurons significantly reduced the number of senescent cells, demonstrating that the direct regulation of p21 levels in SATB1KO DA neurons triggers the senescence phenotype."
    explanation: >-
      Establishes that p21 is the effector between SATB1 loss and the arrest, by blocking CDKN1A and
      reversing the phenotype. This is why the node names p21 rather than describing the SATB1
      effect generically.
  - reference: PMID:34359864
    reference_title: "Alpha-Synuclein Preformed Fibrils Induce Cellular Senescence in Parkinson's Disease Models."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "These results indicate that PFF-induced pathology could lead to astrocyte and/or microglia senescence in PD brains, which may contribute to neuropathology in this model."
    explanation: >-
      The authors' reading of their mouse preformed-fibril experiments. It is the model-system
      counterpart of the human marker findings and the evidence that alpha-synuclein pathology can
      induce glial senescence, stated by the authors as a possibility rather than a demonstrated
      sequence.
- name: Oxidative Stress
  description: >
    Excessive reactive oxygen species from dopamine metabolism and mitochondrial
    dysfunction causes lipid peroxidation, protein carbonylation, and DNA damage.
    Dopamine auto-oxidation generates toxic quinones that preferentially damage
    substantia nigra neurons.
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: Response to Oxidative Stress
    term:
      id: GO:0006979
      label: response to oxidative stress
  - preferred_term: ROS Metabolic Process
    term:
      id: GO:0072593
      label: reactive oxygen species metabolic process
  downstream:
  - target: Mitochondrial Dysfunction
  - target: Dopaminergic Neuron Loss
  - target: Alpha-Synuclein Aggregation
  evidence:
  - reference: PMID:37303175
    reference_title: "Oxidative Stress and Dopaminergic Metabolism: A Major PD Pathogenic Mechanism and Basis of Potential Antioxidant Therapies."
    supports: SUPPORT
    snippet: "Reactive oxygen species (ROS)-induced oxidative stress triggers the vicious cycle leading to the degeneration of dopaminergic neurons in the nigra pars compacta."
    explanation: This review directly describes the mechanism by which oxidative stress drives dopaminergic neurodegeneration.
- name: Calcium Dysregulation
  description: >
    Substantia nigra dopaminergic neurons rely on L-type calcium channels (CaV1.3)
    for autonomous pacemaking, making them uniquely vulnerable to calcium-mediated
    toxicity. Disrupted calcium homeostasis in mitochondria, ER, and lysosomes
    contributes to oxidative stress and cell death.
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: Calcium Ion Homeostasis
    term:
      id: GO:0055074
      label: calcium ion homeostasis
  - preferred_term: Calcium Ion Transport
    term:
      id: GO:0070588
      label: calcium ion transmembrane transport
  downstream:
  - target: Mitochondrial Dysfunction
  - target: Oxidative Stress
  - target: Dopaminergic Neuron Loss
  evidence:
  - reference: PMID:35339179
    reference_title: "The Role of Voltage-Gated Calcium Channels in Basal Ganglia Neurodegenerative Disorders."
    supports: SUPPORT
    snippet: "The dysregulation of VGCC activity has been reported in both Parkinson's disease (PD) and Huntington's (HD)."
    explanation: This review establishes the fundamental role of calcium channel dysregulation in PD pathogenesis.
- name: Endoplasmic Reticulum Stress
  description: >
    Accumulation of misfolded proteins in the ER activates the unfolded protein
    response (UPR). Chronic ER stress overwhelms protective mechanisms, triggering
    apoptotic pathways. Alpha-synuclein aggregates and GBA mutations directly
    impair ER function.
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: ER Stress Response
    term:
      id: GO:0034976
      label: response to endoplasmic reticulum stress
  - preferred_term: Unfolded Protein Response
    term:
      id: GO:0030968
      label: endoplasmic reticulum unfolded protein response
  downstream:
  - target: Autophagy-Lysosome Pathway Dysfunction
  - target: Dopaminergic Neuron Loss
  evidence:
  - reference: PMID:38026955
    reference_title: "Strategies targeting endoplasmic reticulum stress to improve Parkinson's disease."
    supports: SUPPORT
    snippet: "Accumulating evidence shows that endoplasmic reticulum (ER) stress occurring in the SNpc DA neurons is an early event in the development of PD."
    explanation: This review establishes ER stress as an early and central event in PD pathogenesis.
- name: Synaptic Dysfunction
  description: >
    Impaired synaptic vesicle recycling, particularly defects in clathrin-mediated
    endocytosis, represents an early feature of PD. Multiple PD genes (DNAJC6,
    SYNJ1, LRRK2, ITSN1) regulate synaptic vesicle trafficking, and their dysfunction
    leads to synaptic failure before overt neurodegeneration. ITSN1 is a scaffold
    protein that orchestrates clathrin-mediated endocytosis, placing it on this
    convergent node alongside DNAJC6 and SYNJ1.
  genes:
  - preferred_term: DNAJC6
    term:
      id: hgnc:15469
      label: DNAJC6
  - preferred_term: SYNJ1
    term:
      id: hgnc:11503
      label: SYNJ1
  - preferred_term: ITSN1
    term:
      id: hgnc:6183
      label: ITSN1
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: Synaptic Vesicle Cycle
    term:
      id: GO:0099504
      label: synaptic vesicle cycle
  - preferred_term: Synaptic Vesicle Endocytosis
    term:
      id: GO:0048488
      label: synaptic vesicle endocytosis
  molecular_functions:
  - preferred_term: ITSN1 endocytic scaffold adaptor activity
    modifier: DECREASED
    term:
      id: GO:0060090
      label: molecular adaptor activity
  downstream:
  - target: Dopaminergic Neuron Loss
    hypothesis_groups:
    - synaptic_vesicle_endocytosis_convergence
  - target: Alpha-Synuclein Aggregation
    hypothesis_groups:
    - synaptic_vesicle_endocytosis_convergence
  evidence:
  - reference: PMID:40056900
    reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: "ITSN1 encodes a multidomain scaffold protein that orchestrates protein-protein interactions during clathrin-mediated endocytosis and synaptic vesicle recycling."
    explanation: States the clathrin-mediated endocytosis and synaptic-vesicle-recycling role that places ITSN1 on this node. The sentence restates established protein function in the introduction of a human genetics paper, so it is graded OTHER with a BACKGROUND quote role.
  - reference: PMID:38595283
    reference_title: "Dysfunction of synaptic endocytic trafficking in Parkinson's disease."
    supports: SUPPORT
    snippet: "Notably, several of these genes are linked to the synaptic vesicle recycling process, particularly the clathrin-mediated endocytosis pathway. This suggests that impaired synaptic vesicle recycling might represent an early feature of Parkinson's disease"
    explanation: Establishes synaptic vesicle endocytosis dysfunction as an early feature of PD.
  - reference: PMID:23804577
    reference_title: "Mutation in the SYNJ1 gene associated with autosomal recessive, early-onset Parkinsonism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: "SYNJ1 encodes synaptojanin 1, a phosphoinositide phosphatase protein with essential roles in the postendocytic recycling of synaptic vesicles."
    explanation: States the postendocytic synaptic-vesicle recycling role that places SYNJ1 on this node rather than on the mitochondrial node. The sentence restates established protein function in the introduction of a human genetics paper, so it is graded OTHER with a BACKGROUND quote role.
  - reference: PMID:22563501
    reference_title: "A deleterious mutation in DNAJC6 encoding the neuronal-specific clathrin-uncoating co-chaperone auxilin, is associated with juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: "DNAJC6 encodes the HSP40 Auxilin, a protein which is selectively expressed in neurons and confers specificity to the ATPase activity of its partner Hcs70 in clathrin uncoating."
    explanation: States the neuron-specific clathrin-uncoating role that places DNAJC6 on this node. The sentence restates established protein function rather than a result of the cited study, so it is graded OTHER with a BACKGROUND quote role.
- name: Iron Accumulation and Ferroptosis
  description: >
    Abnormal iron deposition in the substantia nigra promotes ferroptosis, an
    iron-dependent form of cell death characterized by lipid peroxidation. Iron
    catalyzes Fenton reactions generating hydroxyl radicals, and dysregulated
    iron metabolism contributes to oxidative damage.
  cell_types:
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  biological_processes:
  - preferred_term: Iron Ion Homeostasis
    term:
      id: GO:0006879
      label: intracellular iron ion homeostasis
  - preferred_term: Ferroptosis
    term:
      id: GO:0097707
      label: ferroptosis
  downstream:
  - target: Oxidative Stress
  - target: Dopaminergic Neuron Loss
  evidence:
  - reference: PMID:39218077
    reference_title: "Ferroptosis in Parkinson's disease -- The iron-related degenerative disease."
    supports: SUPPORT
    snippet: "Parkinson's disease (PD) is a prevalent and advancing age-related neurodegenerative disorder, distinguished by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Iron regional deposit in SNpc is a significant pathological characteristic of PD."
    explanation: This review establishes iron accumulation as a significant pathological characteristic and mechanistic driver of PD.
- name: Blood-Brain Barrier Dysfunction
  description: >
    Altered tight junction proteins, transporter dysfunction, and alpha-synuclein
    accumulation compromise BBB integrity. BBB breakdown allows infiltration of
    peripheral immune cells and blood-borne molecules, amplifying neuroinflammation.
  cell_types:
  - preferred_term: Brain Endothelial Cell
    term:
      id: CL:2000044
      label: brain microvascular endothelial cell
  - preferred_term: Pericyte
    term:
      id: CL:0000669
      label: pericyte
  - preferred_term: Astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: BBB Maintenance
    term:
      id: GO:0035633
      label: maintenance of blood-brain barrier
  - preferred_term: Vascular Permeability
    term:
      id: GO:0043114
      label: regulation of vascular permeability
  downstream:
  - target: Neuroinflammation
  - target: Dopaminergic Neuron Loss
  evidence:
  - reference: PMID:39075566
    reference_title: "Blood-brain barrier alterations and their impact on Parkinson's disease pathogenesis and therapy."
    supports: SUPPORT
    snippet: "There is increasing evidence for blood-brain barrier (BBB) alterations in Parkinson's disease (PD), the second most common neurodegenerative disorder with rapidly rising prevalence."
    explanation: This comprehensive 2024 review establishes BBB dysfunction as an emerging mechanism in PD pathogenesis.
  - reference: PMID:42599550
    reference_title: "Astrocytes orchestrate neuroprotection and pathogenesis via bidirectional neuronal interactions in Parkinson's disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "As the most abundant glial cells in the central nervous system (CNS), astrocytes may exert neuroprotective effects through mechanisms including secretion of neurotrophic factors, regulation of the blood-brain barrier (BBB), and maintenance of water-electrolyte balance."
    explanation: Supports the astrocyte among the cell types regulating the barrier, which is why this node carries astrocyte as a cell type.
- name: Metabolic Dysfunction and Weight Loss
  description: >
    Parkinson disease is associated with progressive weight loss and metabolic dysregulation
    through multiple interacting mechanisms. Reduced metabolic rate, dysregulated appetite-regulating
    hormones (leptin, ghrelin, GLP-1), gastrointestinal dysfunction, cognitive decline affecting
    appetite awareness, dopaminergic-medication effects, and dopamine-dependent regulation of
    feeding behavior all contribute to systemic metabolic failure and weight loss. Weight loss
    occurs in a substantial fraction of PD patients and exerts significant morbidity and mortality,
    yet mechanistic understanding remains incomplete.
  biological_processes:
  - preferred_term: Metabolic process
    term:
      id: GO:0008152
      label: metabolic process
  downstream:
  - target: Weight Loss
    causal_link_type: DIRECT
    description: >
      Metabolic dysregulation, reduced energy expenditure, neuroendocrine hormone
      imbalances, and gastrointestinal dysfunction converge to cause progressive
      weight loss and nutritional decline in PD.
    evidence:
    - reference: PMID:41781031
      reference_title: "When the Scale Drops: Pathways to Weight Loss in Parkinson's Disease and Future Directions."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Emerging research highlights the role of metabolic regulation, neuroendocrine signaling, pharmacologic treatment, cognitive decline, gastrointestinal dysfunction, and brain stimulation in shaping weight trajectories in PD."
      explanation: >
        This review identifies multiple converging pathways that shape weight loss
        in PD, directly supporting metabolic dysfunction as a driver of weight loss.
  evidence:
  - reference: PMID:41781031
    reference_title: "When the Scale Drops: Pathways to Weight Loss in Parkinson's Disease and Future Directions."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "weight loss has long been observed in PD and other neurodegenerative disorders, yet the mechanisms remain incompletely understood. This limited mechanistic insight has left few treatment options for weight loss in PD."
    explanation: >
      This 2026 review establishes weight loss as a significant, mechanistically
      complex, and undertreated symptom of Parkinson disease, establishing the
      rationale for a dedicated metabolic dysfunction mechanism node.
- name: PP2A Phosphatase Activation Failure
  biological_scale: MOLECULAR
  description: >-
    Biallelic PTPA missense variants lower PTPA protein levels and, through that,
    the level of assembled protein phosphatase 2A complex, so the phosphatase is
    not activated normally. PP2A is the major serine/threonine phosphatase of the
    brain, and this node is the molecular step that defines the PARK25 subtype.
  genes:
  - preferred_term: PTPA
    term:
      id: hgnc:9308
      label: PTPA
  molecular_functions:
  - preferred_term: protein serine/threonine phosphatase activity
    term:
      id: GO:0004722
      label: protein serine/threonine phosphatase activity
    modifier: DECREASED
  downstream:
  - target: Striatal Dopamine Deficiency
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Loss of PP2A activation in neurons, inferred from a Drosophila knock-down in which the locomotor defect was reversed by L-DOPA.
    description: >-
      The dopaminergic step is an inference rather than a direct measurement: the
      only functional in vivo result is a levodopa-reversible climbing defect in
      Drosophila, and the affected patients' motor symptoms responded to
      levodopa. No human nigrostriatal dopamine measurement is reported for
      PTPA carriers in the cited work.
    evidence:
    - reference: PMID:36073231
      reference_title: PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      directness: INDIRECT
      snippet: "PTPA orthologue knock-down in Drosophila neurons induced a significant impairment of locomotion in the climbing test. This defect was age-dependent and fully reversed by L-DOPA treatment."
      explanation: A levodopa-reversible motor defect on PTPA knock-down is the basis for placing this node upstream of striatal dopamine deficiency, and the reversal by L-DOPA is what makes the link dopaminergic rather than merely motor.
  evidence:
  - reference: PMID:36073231
    reference_title: PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation"
    explanation: Directly states the decreased PP2A complex level and impaired phosphatase activation that this node asserts.
  - reference: PMID:36073231
    reference_title: PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: "The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signalling pathways and functions"
    explanation: Source for describing PP2A as the brain's major serine/threonine phosphatase, which is why the node binds a serine/threonine phosphatase activity term. The sentence is the paper's framing of established biology, not its own result.
- name: Postsynaptic D2/D3 Receptor Occupancy by Agonist Therapy
  role: therapeutic_vulnerability
  conforms_to: dopamine_receptor_agonism#D2/D3 Receptor Agonist Occupancy
  biological_scale: MOLECULAR
  description: Striatal postsynaptic D2 and D3 receptors remain available to a directly acting agonist as the nigrostriatal terminal is lost, which is why this class works without requiring surviving neurons to take up and decarboxylate levodopa. This is the receptor-occupancy node that dopamine agonist therapy acts on, not a step in the degeneration itself, so it carries no downstream edge into the disease chain.
  molecular_functions:
  - preferred_term: dopamine D2/D3 receptor activation by an agonist drug
    term:
      id: GO:0001591
      label: dopamine neurotransmitter receptor activity, coupled via Gi/Go
    modifier: INCREASED
  locations:
  - preferred_term: striatum
    term:
      id: UBERON:0002435
      label: striatum
  genes:
  - preferred_term: DRD2
    term:
      id: hgnc:3023
      label: DRD2
  - preferred_term: DRD3
    term:
      id: hgnc:3024
      label: DRD3
  evidence:
  - reference: PMID:9617505
    reference_title: "Pharmacology of pramipexole, a dopamine D3-preferring agonist useful in treating Parkinson's disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: DIRECT
    quote_role: REVIEW_SYNTHESIS
    snippet: Third, it has full intrinsic activity at dopamine D2 subfamily receptors.
    explanation: Full agonist activity at the receptor is what lets this class act independently of the failing presynaptic dopamine supply.
phenotypes:
- name: Resting Tremor
  category: Neurological
  frequency: VERY_FREQUENT
  diagnostic: true
  notes: Classic "pill-rolling" tremor at rest
  phenotype_term:
    preferred_term: Resting Tremor
    term:
      id: HP:0002322
      label: Resting tremor
  evidence:
  - reference: PMID:17955331
    reference_title: "The Rotterdam Study: objectives and design update."
    supports: SUPPORT
    snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
    explanation: This identifies resting tremor as a cardinal sign used to detect parkinsonism, supporting it as a core PD phenotype.
- name: Bradykinesia
  category: Neurological
  frequency: VERY_FREQUENT
  diagnostic: true
  notes: Slowness of movement, required for diagnosis
  phenotype_term:
    preferred_term: Bradykinesia
    term:
      id: HP:0002067
      label: Bradykinesia
  evidence:
  - reference: PMID:17955331
    reference_title: "The Rotterdam Study: objectives and design update."
    supports: SUPPORT
    snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
    explanation: This lists bradykinesia among the cardinal signs of parkinsonism, supporting its central role in PD.
- name: Rigidity
  category: Neurological
  frequency: VERY_FREQUENT
  notes: Cogwheel or lead-pipe rigidity
  phenotype_term:
    preferred_term: Rigidity
    term:
      id: HP:0002063
      label: Rigidity
  evidence:
  - reference: PMID:17955331
    reference_title: "The Rotterdam Study: objectives and design update."
    supports: SUPPORT
    snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
    explanation: This confirms rigidity as a cardinal sign of parkinsonism relevant to PD.
- name: Postural Instability
  category: Neurological
  frequency: FREQUENT
  notes: Develops in later disease stages
  phenotype_term:
    preferred_term: Postural Instability
    term:
      id: HP:0002172
      label: Postural instability
  evidence:
  - reference: PMID:17955331
    reference_title: "The Rotterdam Study: objectives and design update."
    supports: SUPPORT
    snippet: "Participants are screened in the baseline and follow-up examinations for cardinal signs of parkinsonism (resting tremor, rigidity, bradykinesia or impaired postural reflexes)."
    explanation: This supports postural instability as a cardinal parkinsonian sign captured in PD assessments.
- name: Hyposmia
  category: Sensory
  frequency: FREQUENT
  notes: Often precedes motor symptoms by years
  phenotype_term:
    preferred_term: Hyposmia
    term:
      id: HP:0004409
      label: Hyposmia
  evidence:
  - reference: PMID:24136244
    reference_title: "Hyposmia: a possible biomarker of Parkinson's disease."
    supports: SUPPORT
    snippet: "Hyposmia, identified as reduced sensitivity to odor, is a common non-motor symptom of Parkinson's disease (PD) that antedates the typical motor symptoms by several years. It occurs in ∼90% of early-stage cases of PD."
    explanation: This establishes hyposmia as a highly prevalent prodromal symptom that precedes motor symptoms, supporting its importance as an early marker of PD.
- name: Constipation
  category: Gastrointestinal
  frequency: FREQUENT
  notes: Common non-motor symptom
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
  evidence:
  - reference: PMID:7845407
    reference_title: "Anorectal manometry in the assessment of anorectal function in Parkinson's disease: a comparison with chronic idiopathic constipation."
    supports: SUPPORT
    snippet: "We investigated the role of anorectal manometry in evaluating constipation and anorectal function in 15 patients with Parkinson's disease (PD) and compared results with those of 9 patients with idiopathic constipation (IC) and 8 control (C) subjects."
    explanation: This study directly evaluates constipation in PD patients, supporting constipation as a common non-motor symptom.
- name: Depression
  category: Psychiatric
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Depression
    term:
      id: HP:0000716
      label: Depression
  evidence:
  - reference: PMID:41301797
    reference_title: "Non-Motor Symptoms as Markers of Disease Severity in Parkinson's Disease: Associations Between Constipation, Depression, REM Sleep Behavior Disorder, and Motor Impairment."
    supports: SUPPORT
    snippet: "Depressive symptoms were similar across groups, but in prodromal PD, higher GDS scores were associated with worse UPDRS III scores (p = 0.02), as well as higher freezing and fall scores."
    explanation: This indicates depressive symptoms are present and clinically relevant in PD, supporting depression as a non-motor phenotype.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "PD patients reported more depression, especially with sleep problems, which also worsened anxiety. Factors like age, motor symptoms, and sleep disturbances relate to depression, while sleep issues are linked to anxiety."
    explanation: >-
      Records the reported association between sleep disturbance and depression
      in PD. The quoted sentence is about sleep disturbance in general rather
      than REM sleep behavior disorder specifically, so it belongs on this
      phenotype; it makes no claim about cognition and recommends no therapy.
- name: REM Sleep Behavior Disorder
  category: Sleep
  notes: >-
    Prodromal non-motor feature that often precedes motor onset by years and
    correlates with greater motor severity. Results from dysfunction of brainstem
    motor inhibition circuits during REM sleep.
  phenotype_term:
    preferred_term: REM sleep behavior disorder
    term:
      id: HP:5200291
      label: REM sleep behavior disorder
  evidence:
  - reference: PMID:41301797
    reference_title: "Non-Motor Symptoms as Markers of Disease Severity in Parkinson's Disease: Associations Between Constipation, Depression, REM Sleep Behavior Disorder, and Motor Impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Constipation and REM sleep behavioral disorder were independent correlates of worse motor severity in prodromal and established PD"
    explanation: >-
      This PPMI-cohort study establishes REM sleep behavior disorder as a
      non-motor feature of both prodromal and established Parkinson disease that
      independently correlates with greater motor severity.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It results from dysfunction of the subcoeruleus and magnocellularis nuclei in the brainstem"
    quote_role: REVIEW_SYNTHESIS
    explanation: >-
      Names the brainstem lesion behind RBD. These nuclei are glutamatergic and
      glycinergic respectively, not dopaminergic, which is the clinical point of
      RBD in PD: it reflects non-dopaminergic brainstem degeneration that
      precedes nigral loss, and so appears in the prodromal phase.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dopamine influences motor and non-motor functions, including cognition, mood, sleep, sensory processes, and autonomic systems"
    quote_role: REVIEW_SYNTHESIS
    explanation: >-
      Records that sleep is among the non-motor functions dopamine influences.
      Kept deliberately narrow: the sentence states dopamine's range of
      influence, and does not assert depletion, a mechanism independent of
      motor circuits, or any claim specific to RBD.
- name: Cognitive Impairment
  category: Cognitive
  frequency: FREQUENT
  notes: >-
    Spans mild cognitive impairment (typically executive and visuospatial
    deficits) through to Parkinson disease dementia; the risk of dementia
    rises with disease duration.
  phenotype_term:
    preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:34210995
    reference_title: "Parkinson disease-associated cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition to the defining motor symptoms of PD, multiple non-motor symptoms occur; among them, cognitive impairment is common and can potentially occur at any disease stage."
    explanation: >-
      This Nature Reviews Disease Primers review establishes cognitive
      impairment as a common non-motor feature of PD that can occur at any
      disease stage.
  - reference: PMID:34210995
    reference_title: "Parkinson disease-associated cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "executive and visuospatial impairments are typical and can be accompanied by memory impairment, increasing the risk for early progression to dementia"
    explanation: >-
      Describes the mild-cognitive-impairment-to-dementia progression that
      underpins the progressive clinical course of cognitive impairment in PD.
- name: Excessive Daytime Somnolence
  category: Sleep
  notes: >
    Persistent daytime sleepiness with brief involuntary sleep episodes ('sleep attacks'),
    often without warning of drowsiness. Associated with increased levodopa doses,
    sleep apnea, and higher rates of depression, hallucinations, and dementia.
  phenotype_term:
    preferred_term: Excessive daytime somnolence
    term:
      id: HP:0001262
      label: Excessive daytime somnolence
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Some of these sudden events are referred to as 'sleep attacks,' and they occur without warning of drowsiness"
    explanation: >
      The review describes excessive daytime sleepiness and sleep attacks as significant
      non-motor manifestations that impact safety and quality of life in PD.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These patients need more levodopa, often have sleep apnea, and show higher rates of depression, hallucinations, and dementia"
    explanation: >
      The review links excessive daytime sleepiness to more severe PD phenotypes, including
      comorbid neuropsychiatric symptoms and the need for higher dopaminergic medication.
- name: Apathy
  category: Psychiatric
  frequency: FREQUENT
  notes: >
    Lack of motivation and interest, distinct from depression (no sadness). Often related
    to loss of dopamine and serotonin. May be more bothersome than depression symptoms
    alone in PD.
  phenotype_term:
    preferred_term: Apathy
    term:
      id: HP:0000741
      label: Apathy
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Apathy is different from depression because it shows no sadness"
    explanation: >
      The review establishes apathy as a distinct non-motor symptom with different phenomenology
      than depression, requiring separate clinical attention and treatment approaches.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "Given the high prevalence of depression, anxiety, and apathy in PD, the goal is to seek tools to manage these aspects of PD."
    explanation: >
      Supports the frequency recorded on this node rather than the phenotype itself:
      the review states apathy is highly prevalent in PD, which the phenomenology
      snippet above does not.
- name: Fatigue
  category: Constitutional
  frequency: FREQUENT
  notes: >
    Common, debilitating non-motor symptom that can occur at any disease stage, even before
    motor symptoms. A subjective, persistent feeling of tiredness disproportionate to activity
    and not relieved by rest. Categorized as physical, mental, emotional; central vs. peripheral;
    and primary vs. secondary (linked to mood or sleep).
  phenotype_term:
    preferred_term: Fatigue
    term:
      id: HP:0012378
      label: Fatigue
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fatigue can occur at any stage, even before motor symptoms. It is a subjective, persistent feeling of tiredness or low energy disproportionate to activity and not relieved by rest"
    explanation: >
      The review emphasizes fatigue as a major quality-of-life concern in PD that is
      often underrecognized despite occurring across all disease stages.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "Fatigue is a common, debilitating non-motor symptom in PD that reduces quality of life"
    explanation: >
      Supports the frequency recorded on this node. The phenomenology snippet above
      establishes what fatigue is in PD and when it appears, not how often.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The study found that individuals who reported exercising had fewer and milder NMS than those who did not exercise"
    directness: INDIRECT
    quote_role: REVIEW_SYNTHESIS
    explanation: >
      The review reports that people with PD who exercised had fewer and milder non-motor
      symptoms, and names fatigue among the non-motor symptoms that study examined. The
      result is an aggregate across those symptoms rather than a fatigue-specific effect
      size, so it bears on this node by inference.
- name: Dystonia
  category: Neurological
  notes: >
    Involuntary sustained or intermittent muscle contractions causing abnormal postures.
    When present in PD, dystonia is predominantly focal, most commonly affecting the lower
    limbs, followed by cervical involvement, and is associated with advanced Hoehn and Yahr
    stage (≥3), younger age at PD onset, and shorter disease duration. A population prevalence
    of dystonia in PD is not established by the cited case-control study, so no frequency band
    is asserted.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:42430982
    reference_title: "Dystonia in Parkinson's disease: Clinical characteristics and predictors of treatment response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Focal dystonia was the predominant phenotype (75.0%), most commonly involving lower limbs, followed by cervical dystonia."
    explanation: >
      This clinical study characterizes the somatotopic distribution of dystonia in PD,
      showing that focal dystonia is the predominant form and lower-limb involvement is most common.
  - reference: PMID:42430982
    reference_title: "Dystonia in Parkinson's disease: Clinical characteristics and predictors of treatment response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Data on 246 PD patients (164 with and 82 without dystonia) were analyzed."
    explanation: >
      Describes the case-control study composition (164 PD patients with dystonia versus 82
      without, drawn from the same source population). The 164:82 split is the study's
      case:control sampling ratio, not a population prevalence, and does not by itself
      quantify how frequently dystonia occurs in PD.
  - reference: PMID:42430982
    reference_title: "Dystonia in Parkinson's disease: Clinical characteristics and predictors of treatment response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "advanced H&Y stage ≥3 (OR, 3.61; P = 0.002) was directly associated with it."
    explanation: >-
      Establishes association between dystonia and advanced Hoehn and Yahr stage,
      supporting dystonia as a clinical marker of disease progression.
  - reference: PMID:42430982
    reference_title: "Dystonia in Parkinson's disease: Clinical characteristics and predictors of treatment response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Levodopa dose increases improved dystonia in 51.6% of patients, and botulinum neurotoxin (BoNT) improved dystonia (OR, 3.01; P = 0.05)."
    explanation: >-
      Documents treatment response patterns for PD-associated dystonia, including
      efficacy of levodopa dose optimization and botulinum neurotoxin injection.
- name: Weight Loss
  category: Constitutional
  notes: >-
    Progressive unintentional weight loss is a well-recognized non-motor feature
    of Parkinson disease, arising from multiple interacting mechanisms (metabolic
    dysregulation, neuroendocrine/appetite-hormone disruption, gastrointestinal
    dysfunction, cognitive decline, and medication effects). It carries
    substantial morbidity and mortality.
  phenotype_term:
    preferred_term: Weight loss
    term:
      id: HP:0001824
      label: Weight loss
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:41781031
    reference_title: "When the Scale Drops: Pathways to Weight Loss in Parkinson's Disease and Future Directions."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "weight loss has long been observed in PD and other neurodegenerative disorders, yet the mechanisms remain incompletely understood. This limited mechanistic insight has left few treatment options for weight loss in PD."
    explanation: >-
      Establishes weight loss as a long-recognized non-motor symptom of Parkinson
      disease with substantial clinical impact.
- name: Impulse Control Behaviors
  category: Psychiatric
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Impulse control behaviors
    term:
      id: HP:0100710
      label: Impulsivity
  notes: >-
    Reward-seeking impulse control behaviors (gambling, hypersexuality, compulsive shopping,
    binge eating) represent a major behavioral comorbidity in PD, particularly in patients
    receiving dopamine agonist therapy. These behaviors arise from dopaminergic sensitization
    of reward-processing circuits and are distinct from classic obsessive-compulsive
    compulsions. Bound to HP:0100710 Impulsivity, which is the closest available HP term;
    preferred_term carries the more specific clinical concept. What HP lacks is a term for
    the dopaminergic-therapy-related ICB syndrome as such - one that distinguishes it from
    trait impulsivity and from HP:0000722 Compulsive behaviors - not a term for impulsivity.
    The frequency band is OCCASIONAL (5-29%): the meta-analytic point estimate is 19%
    (95% CI 15-24%) and the DOMINION cross-sectional estimate is 13.6%, so both the pooled
    estimate and its confidence interval sit inside that band.
  evidence:
  - reference: PMID:20457959
    reference_title: "Impulse control disorders in Parkinson disease: a cross-sectional study of 3090 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An ICD was identified in 13.6% of patients (gambling in 5.0%, compulsive sexual behavior in 3.5%, compulsive buying in 5.7%, and binge-eating disorder in 4.3%), and 3.9% had 2 or more ICDs."
    explanation: >-
      Peer-reviewed point-prevalence estimate from 3090 patients at 46 movement disorder
      centres, with the four constituent behaviors counted separately. Corroborates the
      preprint meta-analysis and independently places the frequency in the OCCASIONAL band.
  - reference: PPR:PPR1298507
    reference_title: "Prevalence and Treatment of Impulse Control Behaviours in Parkinson's Disease: A Meta-Analysis and Systematic Review"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A random-effects meta-analysis of 27 studies (n = 17,906) found a mean event rate for at least one ICB in PD of 0.19 [95% CI = 0.15, 0.24]"
    explanation: >-
      Pooled event rate across 27 studies, giving the 19% (95% CI 15-24%) estimate behind the
      OCCASIONAL band. A non-peer-reviewed preprint, cited alongside the peer-reviewed
      DOMINION prevalence above rather than as sole support.
  - reference: PMID:20457959
    reference_title: "Impulse control disorders in Parkinson disease: a cross-sectional study of 3090 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Impulse control disorders were more common in patients treated with a dopamine agonist than in patients not taking a dopamine agonist (17.1% vs 6.9%; odds ratio [OR], 2.72; 95% confidence interval [CI], 2.08-3.54; P < .001)."
    explanation: >-
      Quantifies dopamine agonist exposure as a risk factor for this phenotype, which is the
      peer-reviewed counterpart of the preprint's qualitative statement below.
  - reference: PPR:PPR1298507
    reference_title: "Prevalence and Treatment of Impulse Control Behaviours in Parkinson's Disease: A Meta-Analysis and Systematic Review"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "mean event rate for at least one ICB in PD of 0.19 [95% CI = 0.15, 0.24], with evidence suggesting higher rates in patients taking dopamine agonists"
    explanation: >-
      The meta-analysis reports the same direction of effect for dopamine agonist exposure,
      qualitatively rather than as an effect size.
- name: Anxiety
  category: Psychiatric
  frequency: FREQUENT
  notes: >-
    Common non-motor symptom manifesting physically (sweating, headaches, sleep issues,
    racing heart, indigestion) and psychologically (panic attacks, worry, compulsive
    behaviors). Reported as interacting with fear and limbic circuitry rather than arising
    only as a reaction to motor disability.
  phenotype_term:
    preferred_term: Anxiety
    term:
      id: HP:0000739
      label: Anxiety
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "Anxiety is a common non-motor symptom of PD, not just a reaction. It manifests physically (sweating, headaches, sleep issues, racing heart, indigestion) and psychologically (panic attacks, worry, unease, nervousness, compulsive behaviors)."
    explanation: >-
      This comprehensive review establishes anxiety as a common neuropsychiatric non-motor
      symptom of PD with both somatic and psychological manifestations.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Changes in anxiety to changes in hypothesized fear and limbic circuits were reported, suggesting PD neuropathology interacts with these pathways to promote anxiety."
    explanation: >
      Points to central fear-processing and limbic circuitry in PD anxiety, rather than
      to depression or a reaction to motor symptoms. The source reports this as a
      hypothesized circuit correlation, so the quote reaches the claim by an inference
      step; the same sentence is graded identically on the limbic pathophysiology edge.
- name: Freezing of Gait
  category: Neurological
  frequency: FREQUENT
  notes: >-
    Complex motor phenomenon where patients experience sudden inability to initiate or continue
    walking, often triggered by environmental factors (doorways, narrow spaces, turns, darkness,
    stress). Involves both motor and non-motor (cognitive, attentional, visuospatial) factors.
  phenotype_term:
    preferred_term: Freezing of gait
    term:
      id: HP:0031825
      label: Freezing of gait
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "FOG is a common and complex symptom in PD, involving both motor and non-motor factors. It occurs when PD patients feel as if their feet are glued to the floor, especially at doorways, during turns, in narrow spaces, changing surfaces, in darkness, or under stress."
    explanation: >-
      This review characterizes freezing of gait as a common, multifactorial symptom with
      motor and non-motor components, describing the contextual triggers and impact on
      quality of life and fall risk in PD.
- name: Insomnia
  category: Sleep
  frequency: FREQUENT
  notes: >-
    Difficulty falling or staying asleep, often with early awakenings, leading to daytime
    fatigue and reduced quality of life. One of the most common sleep disorders in PD and
    correlates with cognitive decline and depression. Deliberately left with no incoming
    causal edge: PMID:42646502 records the frequency and the progression trend but offers
    no mechanism specific to insomnia, and the nearest candidate in its pathophysiology
    table ("sleep fragmentation, and sleep disturbances" under serotonergic raphe loss)
    names a broader sleep phenotype than this node. Wiring it would assert a mechanism the
    cited source does not.
  phenotype_term:
    preferred_term: Insomnia
    term:
      id: HP:0100785
      label: Insomnia
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "It is the most common sleep disorder in PD, increasing with disease progression."
    explanation: >-
      This review identifies insomnia as the most prevalent sleep disorder in PD, with
      frequency increasing as disease progresses and linkage to cognitive decline and
      depression, supporting its importance as a non-motor phenotype.
- name: Hallucinations
  category: Psychiatric
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hallucinations
    term:
      id: HP:0000738
      label: Hallucinations
  evidence:
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: "PD psychosis (PDP) is a common neuropsychiatric condition where PwP experience hallucinations and delusions"
    explanation: >-
      Supports the frequency recorded here: the review calls the syndrome in
      which hallucinations occur a common neuropsychiatric condition of PD.
stages:
- name: "Stage 1: Unilateral Disease"
  description: >
    Symptoms are present on one side of the body only. Mild unilateral involvement
    with minimal or no functional impairment. Patients may exhibit resting tremor,
    rigidity, or bradykinesia on one limb or side. Daily activities are not
    significantly affected.
  evidence:
  - reference: PMID:27918765
    reference_title: "Development of a Biochemical Diagnosis of Parkinson Disease by Detection of α-Synuclein Misfolded Aggregates in Cerebrospinal Fluid."
    supports: SUPPORT
    snippet: "the Hoehn and Yahr scale, with the lowest grade indicating unilateral involvement with minimal or no functional impairment"
    explanation: This describes Stage 1 (the lowest grade) as unilateral involvement with minimal or no functional impairment.
  - reference: PMID:34461264
    reference_title: "The cross-hemispheric nigrostriatal pathway prevents the expression of levodopa-induced dyskinesias."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Clinical findings indicate that LID typically only occurs following the progression of PD motor symptoms from the unilateral (Hoehn and Yahr (HY) Stage I) to the bilateral stage (HY Stage II)."
    explanation: This identifies Stage I as the unilateral phase of PD motor symptoms.
  notes: >
    Original Hoehn and Yahr staging scale from 1967 (PMID:6067254). A modified
    scale with 0.5 increments (Stages 1.5, 2.5) has been widely adopted but
    lacks formal clinimetric validation.
- name: "Stage 2: Bilateral Disease Without Balance Impairment"
  description: >
    Symptoms are present on both sides of the body or at the midline. Bilateral
    involvement without impairment of balance. Patients show bilateral tremor,
    rigidity, and bradykinesia but maintain normal postural reflexes and physical
    independence.
  evidence:
  - reference: PMID:34461264
    reference_title: "The cross-hemispheric nigrostriatal pathway prevents the expression of levodopa-induced dyskinesias."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Clinical findings indicate that LID typically only occurs following the progression of PD motor symptoms from the unilateral (Hoehn and Yahr (HY) Stage I) to the bilateral stage (HY Stage II)."
    explanation: This identifies Stage II as the bilateral stage of PD motor symptom progression.
  - reference: PMID:15372591
    reference_title: "Movement Disorder Society Task Force report on the Hoehn and Yahr staging scale: status and recommendations."
    supports: SUPPORT
    snippet: "the scale fulfills at least some criteria for reliability and validity, especially for the midranges of the scale (Stages 2-4)."
    explanation: The MDS Task Force report validates the reliability of midrange stages (2-4) of the Hoehn and Yahr scale.
- name: "Stage 3: Bilateral Disease With Postural Instability"
  description: >
    Mild to moderate bilateral disease with early postural instability. The first
    sign of impaired righting reflexes appears. Patients remain physically
    independent in daily activities but have clinically evident balance impairment.
  evidence:
  - reference: PMID:20181069
    reference_title: "Depression, extrapyramidal symptoms, dementia and an unexpected outcome: a case report."
    supports: SUPPORT
    snippet: "The modified Hoehn and Yahr scale was 3: mild to moderate bilateral disease; some postural instability; physically independent."
    explanation: This directly defines Stage 3 as mild to moderate bilateral disease with some postural instability while remaining physically independent.
  - reference: PMID:15372591
    reference_title: "Movement Disorder Society Task Force report on the Hoehn and Yahr staging scale: status and recommendations."
    supports: SUPPORT
    snippet: "Because the HY scale is weighted heavily toward postural instability as the primary index of disease severity, it does not capture completely impairments or disability from other motor features of PD and gives no information on nonmotor problems."
    explanation: This highlights that the Hoehn and Yahr scale weights postural instability as a primary severity index, providing context for why balance impairment becomes central at Stage 3.
- name: "Stage 4: Severe Disability, Still Ambulatory"
  description: >
    Fully developed, severely disabling disease. Patients remain ambulatory but
    have marked loss of independence in daily activities. More than half require
    assistance with most activities of daily living, despite retained ability to
    complete walk-based assessments.
  evidence:
  - reference: PMID:34125001
    reference_title: "Effect of Lee Silverman Voice Treatment (LSVT)® BIG on motor symptoms in a patient with severe Parkinson's disease: a case report."
    supports: SUPPORT
    snippet: "Her disease severity was classified as Hoehn and Yahr stage 4. The unified Parkinson's disease rating scale (UPDRS) part 3, 10-m walk test (10MWT), timed up-and-go test (TUG), Berg balance scale (BBS), and 30-s chair stand test (30-s CST) were used for assessment before and after intervention."
    explanation: This stage 4 case report shows that advanced patients can remain ambulatory enough to perform walk-based assessments despite severe motor impairment.
  - reference: PMID:40162911
    reference_title: "Profile of Independence in Activities of Daily Living Among Patients With Parkinson's Disease: A Retrospective Observational Study."
    supports: SUPPORT
    snippet: "In the H-Y Stage 4 group, more than half of the patients required assistance with most ADLs, except feeding and bowel control."
    explanation: This directly supports substantial dependence in daily activities as a defining functional feature of Stage 4 disease.
- name: "Stage 5: Wheelchair-Bound or Bedridden"
  description: >
    Patient is confined to wheelchair or bedridden unless aided. Complete
    dependence on caregivers for all activities. Represents the most severe
    stage of motor disability in Parkinson's disease.
  evidence:
  - reference: PMID:27918765
    reference_title: "Development of a Biochemical Diagnosis of Parkinson Disease by Detection of α-Synuclein Misfolded Aggregates in Cerebrospinal Fluid."
    supports: SUPPORT
    snippet: "the highest grade defining patients with complete confinement to wheelchair or bed."
    explanation: This directly defines Stage 5 (the highest grade) as complete confinement to wheelchair or bed.
genetic:
- name: SNCA
  gene_term:
    preferred_term: SNCA
    term:
      id: hgnc:11138
      label: SNCA
  association: Causative
  relationship_type: CAUSATIVE
  notes: Alpha-synuclein gene, autosomal dominant forms
  evidence:
  - reference: PMID:9197268
    reference_title: "Mutation in the alpha-synuclein gene identified in families with Parkinson's disease."
    supports: SUPPORT
    snippet: "A mutation was identified in the alpha-synuclein gene, which codes for a presynaptic protein thought to be involved in neuronal plasticity, in the Italian kindred and in three unrelated families of Greek origin with autosomal dominant inheritance for the PD phenotype."
    explanation: This landmark 1997 Science paper identified the first SNCA mutations in familial PD with autosomal dominant inheritance, establishing SNCA as a causative gene for Parkinson's disease.
  - reference: CGGV:assertion_d21593ae-ed10-4442-8167-24f96f917302-2022-05-03T134931.425Z
    reference_title: "SNCA / Parkinson disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SNCA | HGNC:11138 | Parkinson disease | MONDO:0005180 | AD | Definitive"
    explanation: ClinGen classifies the SNCA-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.
- name: LRRK2
  gene_term:
    preferred_term: LRRK2
    term:
      id: hgnc:18618
      label: LRRK2
  association: Risk Factor
  relationship_type: CAUSATIVE
  notes: >-
    Most common genetic cause of late-onset PD; G2019S acts as an
    autosomal-dominant causative allele with reduced (age-dependent)
    penetrance, so it is often described clinically as a risk factor.
  evidence:
  - reference: PMID:19945904
    reference_title: "Worldwide frequency of G2019S LRRK2 mutation in Parkinson's disease: a systematic review."
    supports: SUPPORT
    snippet: "The LRRK2 G2019S mutation is the most frequent known cause of familial and sporadic Parkinson's disease."
    explanation: This systematic review establishes that LRRK2 G2019S is the most common genetic cause of both familial and sporadic PD, supporting its role as the major genetic risk factor.
  - reference: CGGV:assertion_2728e13a-b95a-4c55-8cba-082260094ecd-2021-05-03T160000.000Z
    reference_title: "LRRK2 / Parkinson disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "LRRK2 | HGNC:18618 | Parkinson disease | MONDO:0005180 | AD | Definitive"
    explanation: ClinGen classifies the LRRK2-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.
  - reference: PMID:38750146
    reference_title: "Sex-dependent interactions between prodromal intestinal inflammation and LRRK2 G2019S in mice promote endophenotypes of Parkinson's disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Chronic intestinal damage in genetically predisposed male mice promotes α-synuclein aggregation in the substantia nigra, loss of dopaminergic neurons and motor impairment."
    explanation: >-
      Offers a candidate explanation for the incomplete, age-dependent
      penetrance recorded in the notes above: in human LRRK2 G2019S transgenic
      mice a prodromal gut-inflammatory insult is what converts the genotype
      into nigral alpha-synuclein aggregation, dopaminergic loss, and motor
      impairment, and the effect is restricted to males. Whether the same
      gene-environment interaction modifies penetrance in human carriers is
      untested.
- name: PINK1
  gene_term:
    preferred_term: PINK1
    term:
      id: hgnc:14581
      label: PINK1
  association: Causative
  relationship_type: CAUSATIVE
  notes: Mitochondrial kinase, autosomal recessive
  evidence:
  - reference: PMID:25611507
    reference_title: "The roles of PINK1, parkin, and mitochondrial fidelity in Parkinson's disease."
    supports: SUPPORT
    snippet: "Biochemical and genetic studies reveal that the products of two genes that are mutated in autosomal recessive parkinsonism, PINK1 and Parkin, normally work together in the same pathway to govern mitochondrial quality control, bolstering previous evidence that mitochondrial damage is involved in Parkinson's disease."
    explanation: This identifies PINK1 mutations in autosomal recessive parkinsonism, supporting its causative role in PD.
  - reference: CGGV:assertion_1999e6c4-eb15-438a-a4ea-98989112dcbb-2023-01-18T190000.000Z
    reference_title: "PINK1 / Parkinson disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "PINK1 | HGNC:14581 | Parkinson disease | MONDO:0005180 | AR | Definitive"
    explanation: ClinGen classifies the PINK1-Parkinson disease gene-disease relationship as definitive with autosomal recessive inheritance.
- name: GBA1
  gene_term:
    preferred_term: GBA1
    term:
      id: hgnc:4177
      label: GBA
  association: Risk Factor
  relationship_type: RISK_FACTOR
  notes: >-
    Glucocerebrosidase (GBA1); the single most common genetic risk factor for
    PD. Heterozygous variants confer risk with reduced penetrance (ClinGen
    reports the assertion under an autosomal-dominant MOI).
  evidence:
  - reference: PMID:30097731
    reference_title: "The Genetics of Dementia with Lewy Bodies: Current Understanding and Future Directions."
    supports: SUPPORT
    snippet: "DLB shares risk loci with AD, in the APOE E4 allele, and with PD, in variation at GBA and SNCA."
    explanation: This identifies GBA as a genetic risk locus shared with PD, supporting its role as a PD risk factor.
  - reference: CGGV:assertion_9201c03f-10de-447c-9b84-194f14b549b6-2022-05-03T134810.206Z
    reference_title: "GBA1 / Parkinson disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "GBA1 | HGNC:4177 | Parkinson disease | MONDO:0005180 | AD | Definitive"
    explanation: ClinGen classifies the GBA1-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.
- name: PARK7
  gene_term:
    preferred_term: PARK7
    term:
      id: hgnc:16369
      label: PARK7
  association: Causative
  relationship_type: CAUSATIVE
  notes: DJ-1 (PARK7); biallelic variants cause early-onset autosomal-recessive PD.
  evidence:
  - reference: CGGV:assertion_d79439d2-844b-4ba6-aceb-e6b179eaaa01-2022-06-27T160000.000Z
    reference_title: "PARK7 / Parkinson disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "PARK7 | HGNC:16369 | Parkinson disease | MONDO:0005180 | AR | Definitive"
    explanation: ClinGen classifies the PARK7-Parkinson disease gene-disease relationship as definitive with autosomal recessive inheritance.
- name: PRKN
  gene_term:
    preferred_term: PRKN
    term:
      id: hgnc:8607
      label: PRKN
  association: Causative
  relationship_type: CAUSATIVE
  notes: >-
    Parkin (PRKN; formerly PARK2). Biallelic loss-of-function variants cause
    early-onset autosomal-recessive PD.
  evidence:
  - reference: PMID:25611507
    reference_title: "The roles of PINK1, parkin, and mitochondrial fidelity in Parkinson's disease."
    supports: SUPPORT
    snippet: "Biochemical and genetic studies reveal that the products of two genes that are mutated in autosomal recessive parkinsonism, PINK1 and Parkin, normally work together in the same pathway to govern mitochondrial quality control, bolstering previous evidence that mitochondrial damage is involved in Parkinson's disease."
    explanation: This establishes Parkin (PRKN, formerly PARK2) as a gene mutated in autosomal recessive parkinsonism, supporting its causative role.
  - reference: CGGV:assertion_6b39c4a0-f6bd-4afc-b2a7-f234eab5a667-2023-01-18T190000.000Z
    reference_title: "PRKN / Parkinson disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "PRKN | HGNC:8607 | Parkinson disease | MONDO:0005180 | AR | Definitive"
    explanation: ClinGen classifies the PRKN-Parkinson disease gene-disease relationship as definitive with autosomal recessive inheritance.
- name: VPS35
  gene_term:
    preferred_term: VPS35
    term:
      id: hgnc:13487
      label: VPS35
  association: Causative
  relationship_type: CAUSATIVE
  notes: >-
    Retromer component VPS35 (D620N); autosomal-dominant late-onset PD.
  evidence:
  - reference: CGGV:assertion_b0e546d6-8a44-4e9d-83aa-f781ec4ec166-2021-11-03T134517.796Z
    reference_title: "VPS35 / Parkinson disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "VPS35 | HGNC:13487 | Parkinson disease | MONDO:0005180 | AD | Definitive"
    explanation: ClinGen classifies the VPS35-Parkinson disease gene-disease relationship as definitive with autosomal dominant inheritance.
- name: CHCHD2
  gene_term:
    preferred_term: CHCHD2
    term:
      id: hgnc:21645
      label: CHCHD2
  association: Causative
  relationship_type: CAUSATIVE
  subtype: PARK22
  inheritance:
  - name: Autosomal dominant
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
  notes: >-
    CHCHD2 (PARK22) is a mitochondrial protein that binds cytochrome c and is
    required for normal crista structure. The discovery study reported variants
    segregating in a Japanese autosomal-dominant late-onset family and in three
    further families, but concluded only that they are associated with, and
    might cause, the disease. The ClinGen Gene-Disease Validity table lists no
    CHCHD2-Parkinson disease assertion (checked 2026-09-25), so this record is
    curated as causative at the locus level with that limitation stated rather
    than as an established definitive gene.
  evidence:
  - reference: PMID:25662902
    reference_title: "CHCHD2 mutations in autosomal dominant late-onset Parkinson's disease: a genome-wide linkage and sequencing study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CHCHD2 mutations are associated with, and might be a cause of, autosomal dominant Parkinson's disease."
    explanation: The authors' own conclusion about the gene-disease relationship, quoted rather than strengthened.
  - reference: PMID:28589937
    reference_title: "Loss of Parkinson's disease-associated protein CHCHD2 affects mitochondrial crista structure and destabilizes cytochrome c."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The loss of CHCHD2 in Drosophila causes abnormal matrix structures and impaired oxygen respiration in mitochondria, leading to oxidative stress, dopaminergic neuron loss and motor dysfunction with age."
    explanation: Provides the mitochondrial mechanism that links CHCHD2 loss to dopaminergic degeneration, and is the basis for binding CHCHD2 to the mitochondrial dysfunction node.
- name: PTPA
  gene_term:
    preferred_term: PTPA
    term:
      id: hgnc:9308
      label: PTPA
  association: Causative
  relationship_type: CAUSATIVE
  subtype: PARK25
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  notes: >-
    PTPA, for which HGNC records PPP2R4 as a previous symbol, encodes a major
    activator of protein phosphatase 2A. Biallelic missense variants were
    reported in a South African and a Libyan family with early-onset
    parkinsonism and intellectual disability, and a third consanguineous family
    was found by independent cross-ethnic screening. The ClinGen Gene-Disease
    Validity table lists no PTPA-Parkinson disease assertion (checked
    2026-09-25).
  evidence:
  - reference: PMID:36073231
    reference_title: PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability."
    explanation: Establishes PTPA as a recessive cause and names the biochemical consequence.
  - reference: PMID:36073231
    reference_title: PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We first identified a homozygous PTPA variant, c.893T>G (p.Met298Arg), in patients from a South African family with early-onset parkinsonism and intellectual disability."
    explanation: Documents the index family and its homozygous genotype.
  - reference: PMID:37046398
    reference_title: "Cross-Ethnic Variant Screening and Burden Analysis of PTPA in Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One patient with early-onset PD from a consanguineous family carried the homozygous variant p.Met329Val, while her parents and elder sister with heterozygous p.Met329Val were healthy."
    explanation: Independent replication in a cohort of 2743 cases and 8177 controls, with heterozygous relatives unaffected.
- name: VPS13C
  gene_term:
    preferred_term: VPS13C
    term:
      id: hgnc:23594
      label: VPS13C
  association: Causative
  relationship_type: CAUSATIVE
  subtype: PARK23
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  notes: >-
    Biallelic truncating VPS13C variants cause recessive early-onset
    parkinsonism with rapid progression and early cognitive decline. The ClinGen
    Gene-Disease Validity table lists no VPS13C-Parkinson disease assertion
    (checked 2026-09-25).
  evidence:
  - reference: PMID:26942284
    reference_title: Loss of VPS13C Function in Autosomal-Recessive Parkinsonism Causes Mitochondrial Dysfunction and Increases PINK1/Parkin-Dependent Mitophagy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This work suggests that loss of function of VPS13C is a cause of autosomal-recessive early-onset parkinsonism with a distinctive phenotype of rapid and severe progression."
    explanation: Establishes biallelic VPS13C loss of function as a cause of recessive early-onset parkinsonism.
  - reference: PMID:26942284
    reference_title: Loss of VPS13C Function in Autosomal-Recessive Parkinsonism Causes Mitochondrial Dysfunction and Increases PINK1/Parkin-Dependent Mitophagy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Silencing of VPS13C was associated with lower mitochondrial membrane potential, mitochondrial fragmentation, increased respiration rates, exacerbated PINK1/Parkin-dependent mitophagy, and transcriptional upregulation of PARK2 in response to mitochondrial damage."
    explanation: Cell-model basis for binding VPS13C to the mitochondrial dysfunction node.
- name: SYNJ1
  gene_term:
    preferred_term: SYNJ1
    term:
      id: hgnc:11503
      label: SYNJ1
  association: Causative
  relationship_type: CAUSATIVE
  subtype: PARK20
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  notes: >-
    Synaptojanin 1 (PARK20). Biallelic variants cause recessive early-onset
    parkinsonism with dystonia and cognitive deterioration. The only SYNJ1 row
    in the ClinGen Gene-Disease Validity table is for genetic developmental and
    epileptic encephalopathy (MONDO:0100062), not for Parkinson disease (checked
    2026-09-25), so the Parkinson relationship here rests on the primary
    literature rather than on a ClinGen classification.
  evidence:
  - reference: PMID:23804577
    reference_title: "Mutation in the SYNJ1 gene associated with autosomal recessive, early-onset Parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we report the identification, by homozygosity mapping and exome sequencing, of a SYNJ1 homozygous mutation (p.Arg258Gln) segregating with disease in an Italian consanguineous family with Parkinsonism, dystonia, and cognitive deterioration."
    explanation: Identifies the segregating biallelic SYNJ1 variant and the phenotype.
  - reference: PMID:23804577
    reference_title: "Mutation in the SYNJ1 gene associated with autosomal recessive, early-onset Parkinsonism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: "SYNJ1 encodes synaptojanin 1, a phosphoinositide phosphatase protein with essential roles in the postendocytic recycling of synaptic vesicles."
    explanation: States the synaptic-vesicle recycling function that places SYNJ1 on the synaptic dysfunction node. The sentence restates established protein function rather than a finding of this study, so it is graded OTHER with a BACKGROUND quote role.
- name: DNAJC6
  gene_term:
    preferred_term: DNAJC6
    term:
      id: hgnc:15469
      label: DNAJC6
  association: Causative
  relationship_type: CAUSATIVE
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:33983693
      reference_title: "DNAJC6 Parkinson Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: REVIEW_SYNTHESIS
      snippet: "DNAJC6 Parkinson disease is inherited in an autosomal recessive manner."
      explanation: >-
        The GeneReviews chapter's genetic-counseling statement, sourcing the
        inheritance mode recorded here.
  notes: >-
    Auxilin, the neuron-specific clathrin-uncoating co-chaperone. Biallelic
    DNAJC6 variants span a juvenile form (PARK19A) and a milder early-onset form
    with onset in the third to fifth decade (PARK19B), so this record carries no
    single subtype reference and both subtype rows are bound instead. The
    ClinGen Gene-Disease Validity table lists no DNAJC6-Parkinson disease
    assertion (checked 2026-09-25); a GeneReviews chapter does exist, listed in
    the committed Bookshelf index as PMID:33983693 'DNAJC6 Parkinson Disease.'
    That chapter also records an avoidance caution rather than a treatment:
    "Dopamine antagonists and vesicular monoamine transporter 2 (VMAT2)
    inhibitors should be avoided as they could aggravate dopamine deficiency."
    It is recorded here rather than as a treatments entry because it names a
    class to withhold, not an intervention to give.
  evidence:
  - reference: PMID:22563501
    reference_title: "A deleterious mutation in DNAJC6 encoding the neuronal-specific clathrin-uncoating co-chaperone auxilin, is associated with juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Using homozygosity mapping and whole exome sequencing we identified a deleterious mutation in DNAJC6 in two patients with juvenile parkinsonism."
    explanation: Original identification of DNAJC6 in juvenile parkinsonism.
  - reference: PMID:22563501
    reference_title: "A deleterious mutation in DNAJC6 encoding the neuronal-specific clathrin-uncoating co-chaperone auxilin, is associated with juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: "DNAJC6 encodes the HSP40 Auxilin, a protein which is selectively expressed in neurons and confers specificity to the ATPase activity of its partner Hcs70 in clathrin uncoating."
    explanation: States the clathrin-uncoating function that places DNAJC6 on the synaptic dysfunction node. The sentence restates established protein function rather than a finding of this study, so it is graded OTHER with a BACKGROUND quote role.
  - reference: PMID:26528954
    reference_title: "DNAJC6 Mutations Associated With Early-Onset Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings delineate a novel form of hereditary early-onset PD."
    explanation: Extends the DNAJC6 phenotype from juvenile parkinsonism to early-onset Parkinson disease, which is the basis for curating two subtype rows.
  - reference: PMID:42414182
    reference_title: "Novel Homozygous Pathogenic Variant in DNAJC6 Causes Rapid Progressive Parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report two siblings (17 and 14 years) harboring a novel homozygous nonsense variant in DNAJC6, p.Cys325*, not previously described in the medical literature and absent from population databases."
    explanation: Reports a novel biallelic DNAJC6 nonsense variant in two affected siblings, absent from population databases.
    quote_role: PRIMARY_RESULT
  - reference: PMID:42414182
    reference_title: "Novel Homozygous Pathogenic Variant in DNAJC6 Causes Rapid Progressive Parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "The variant is predicted to truncate the protein, supporting a loss-of-function mechanism consistent with the gene's disease biology."
    explanation: Gives the predicted consequence of the nonsense variant, supporting a loss-of-function mechanism for the DNAJC6 allele.
- name: FBXO7
  gene_term:
    preferred_term: FBXO7
    term:
      id: hgnc:13586
      label: FBXO7
  association: Causative
  relationship_type: CAUSATIVE
  subtype: PARK15
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  notes: >-
    F-box protein 7 (PARK15). Biallelic variants cause early-onset parkinsonism
    with pyramidal tract signs. The ClinGen Gene-Disease Validity table lists no
    FBXO7-Parkinson disease assertion (checked 2026-09-25).
  evidence:
  - reference: PMID:19038853
    reference_title: "FBXO7 mutations cause autosomal recessive, early-onset parkinsonian-pyramidal syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclusively show that recessive FBXO7 mutations cause progressive neurodegeneration with extrapyramidal and pyramidal system involvement, delineating a novel genetically defined entity that we propose to designate as PARK15."
    explanation: Establishes FBXO7 as a recessive cause of the parkinsonian-pyramidal phenotype.
  - reference: PMID:23933751
    reference_title: "The Parkinson's disease-linked proteins Fbxo7 and Parkin interact to mediate mitophagy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here we show that Fbxo7 participates in mitochondrial maintenance through direct interaction with PINK1 and Parkin and acts in Parkin-mediated mitophagy."
    explanation: Places FBXO7 in the PINK1/parkin mitophagy pathway, which is the basis for binding it to the mitochondrial dysfunction node.
- name: ITSN1
  gene_term:
    preferred_term: ITSN1
    term:
      id: hgnc:6183
      label: ITSN1
  association: Risk Factor
  relationship_type: RISK_FACTOR
  notes: >-
    Rare protein-truncating variants (haploinsufficiency) carry an odds ratio
    of about 10 in the UK Biobank, replicated in three further cohorts. ITSN1
    is a scaffold for clathrin-mediated endocytosis and synaptic vesicle
    recycling, the same pathway as DNAJC6 and SYNJ1. No ClinGen gene-disease
    validity assertion exists for ITSN1 and Parkinson disease, so none is
    recorded.
  evidence:
  - reference: PMID:40056900
    reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we discover that protein-truncating variants in ITSN1 confer a
      substantially increased risk of PD
    explanation: >-
      Whole-genome sequencing of 3,809 PD cases and 247,101 controls identifies
      ITSN1 loss-of-function variants as a PD risk factor.
  - reference: PMID:40056900
    reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We replicate this association in three independent datasets totaling
      8,407 cases and 413,432 controls
    explanation: Independent replication of the ITSN1 association.
environmental:
- name: Pesticide Exposure
  exposure_term:
    preferred_term: exposure to pesticide
    term:
      id: ECTO:0000530
      label: exposure to pesticide
  disease_effect: PREDISPOSES
  causal_role: RISK_FACTOR
  description: >-
    Ambient and occupational exposure to agricultural pesticides raises the risk of the
    disease. The best-resolved human evidence is a pesticide-wide association study in the
    Parkinson's Environment and Genes (PEG) case-control study, which tested 288 individual
    active ingredients against record-based exposure estimates and associated 25 of them at
    FDR 0.01 or below. The compounds in chemicals are that screen's associated active
    ingredients, with two exceptions: rotenone and paraquat carry the longest-standing link to
    the disease but are not hits of this screen, because paraquat dichloride was held out of it
    and reported separately and rotenone enters only as prior work. The one compound with its
    own measured mechanism carries its own entry, Trifluralin Exposure.
  chemicals:
  - trifluralin
  - dicofol
  - propargite
  - tribufos
  - diquat dibromide
  - folpet
  - naled
  - endosulfan
  - copper sulfate
  - endothall
  - sodium chlorate
  - prometryn
  - methomyl
  - rotenone
  - paraquat
  exposure_classifications:
    hazard_agent_type:
    - classification_value: CHEMICAL
    exposure_route:
    - classification_value: UNKNOWN
      notes: >-
        Neither cited design resolves the route. The PEG model estimates pounds applied per
        acre within 500 m of residential and workplace addresses, which is proximity to
        application rather than measured uptake, and the Agricultural Health Study arm rests
        on self-reported ever-use. Inhalation of drift and dermal uptake during handling are
        the usual proposals for agricultural exposure, but neither study measures them, so
        the route is recorded as not established rather than assumed.

        One study has tried to separate an ingestion route from an airborne one, and it
        leaves the assignment unchanged. The golf-course proximity study (PMID:40338549)
        reports nearly doubled odds for residents of a municipal groundwater service area
        containing a golf course. That estimate is adjusted for demographics, income,
        rural-urban classification and healthcare utilisation, and not for distance to the
        course, so it does not separate a drinking-water route from proximity: a service
        area containing a course is itself partly a proximity measure. The estimate in that
        paper that is adjusted for proximity is a different contrast - vulnerable against
        nonvulnerable groundwater regions, 1.99 (95% CI 1.30-3.04) adjusting for proximity
        as a category and 2.02 (1.33-3.09) adjusting for it as linear splines. That one
        concerns aquifer vulnerability rather than golf courses, so it indicates that
        something about the groundwater matters without identifying an agent or tying it to
        course application.

        Three further things stop an oral route being recorded. The paper's own well-based
        proxies are null: no association with a shallow municipal well in the service area
        (aOR 0.63, 95% CI 0.24-1.64) or with a municipal well sited on a golf course (0.56,
        0.21-1.50), and those are the closest available tests of course pesticides reaching
        a drinking supply. A meta-analysis of 15 case-control studies of well-water
        consumption is null overall and null in exactly the two strata that match that
        study's design, American and population-based. And no pesticide was measured in
        water, air or any participant in either study, so the agent on any route remains
        inferred.

        The airborne route is deliberately not recorded even as a candidate. The proximity
        study reads its stronger urban association as airborne drift, but the same authors
        had already reported a PM2.5 association in the same Rochester Epidemiology Project
        cases, greatest in metropolitan cores (PMID:39283636). Both papers draw from one
        series of 450 incident Olmsted County cases, retaining 419 and 346, so at least 315
        cases - 75% of the proximity study's total - are shared. The urban gradient is
        therefore not independent corroboration of an inhalation route.
      evidence:
      - reference: PMID:34938078
        reference_title: "Well-Water Consumption and Risk of Parkinson's Disease: A Meta-Analysis of 15 Observational Studies."
        supports: SUPPORT
        evidence_source: HUMAN_CLINICAL
        snippet: "The combined OR for ever well-water drinkers versus non-drinkers was 1.16 ... Our results indicate that there is no significant correlation between well-water consumption and PD risk."
        explanation: >-
          Supports leaving the route unassigned rather than recording ingestion. Pools 15
          case-control studies, 2182 cases and 2456 controls, on ever-use of well water as
          drinking water. The combined estimate is 1.16 (95% CI 0.97-1.39) and the strata
          matching a US population-based design are flat: America 0.97 (0.76-1.24),
          population-based case-control 0.96 (0.73-1.26). The signal sits in the
          hospital-based (1.31, 1.04-1.65) and Asian (1.29, 1.05-1.58) subgroups, the
          designs more exposed to recall and selection bias. This is context and not a
          refutation of PMID:40338549: the pooled exposure is private-well consumption while
          that study's positive result is municipal groundwater in a service area containing
          a golf course, and private-well users were its lower-risk comparator. The two are
          consistent with well water in itself not carrying the risk. Three caveats travel
          with it: extraction and quality scoring were done by a single reviewer rather than
          duplicated, studies with more than 10,000 participants were excluded, and the
          included studies were published between 1990 and 2014.
      - reference: PMID:39283636
        reference_title: "Air Pollution and Parkinson Disease in a Population-Based Study."
        supports: SUPPORT
        evidence_source: HUMAN_CLINICAL
        snippet: "Greater PM2.5 exposure was associated with increased PD risk, and this risk was greatest after restricting to populations within metropolitan cores"
        explanation: >-
          Supports leaving the route unassigned by removing the basis for an airborne
          assignment. The golf-course proximity study infers airborne pesticide drift from a
          stronger association in urban areas, but this earlier paper by the same authors
          reports an urban-concentrated PM2.5 association in the same Rochester Epidemiology
          Project case series. Both start from 450 incident Olmsted County cases and retain
          419 and 346 respectively, so at least 315 cases are common to both. The urban
          gradient one paper attributes to pesticide drift and the gradient the other
          attributes to particulate matter are measured in largely the same people, so the
          proximity study's urban finding is not independent evidence for an inhalation
          route for pesticides.
    exposure_duration:
    - classification_value: CHRONIC
      notes: >-
        ATSDR chronic duration (365 days and longer). PEG averaged annual estimates across a
        window from 1974 to 10 years before the index date, on average 22 years for
        residential and 18 years for workplace exposure, the lag allowing for a prodromal
        period. The human exposure is chronic and low-dose, while the cell experiments that
        supply the mechanism are acute and high-dose, so the two sit at opposite ends of this
        axis and a mechanism measured in the dish does not transfer to the exposure without
        that caveat.
    exposome_domain:
    - classification_value: SPECIFIC_EXTERNAL
  influences_mechanisms:
  - target: Mitochondrial Dysfunction
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Rotenone directly inhibits mitochondrial complex I in the animal model. Human evidence
      concerns the association of pesticide exposure with Parkinson disease. The rat model also
      reproduces alpha-synuclein-containing nigral inclusions; this model observation does not
      establish that pathology as a human consequence of pesticide exposure.
    evidence:
    - reference: PMID:11100151
      reference_title: "Chronic systemic pesticide exposure reproduces features of Parkinson's disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We report that chronic, systemic inhibition of complex I by the lipophilic pesticide, rotenone, causes highly selective nigrostriatal dopaminergic degeneration that is associated behaviorally with hypokinesia and rigidity"
      explanation: >-
        Names the pesticide, the complex I inhibition this node holds, and the nigrostriatal
        degeneration downstream of it. Rat work, so it carries the mechanism without establishing it
        in human disease. The animal-model evidence does not by itself establish pesticide-induced
        mitochondrial pathology or nigral inclusions in human disease.
    - reference: PMID:15177059
      reference_title: "Occupational and environmental risk factors for Parkinson's disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "there is general agreement that smoking and exposure to pesticides affect the probability of developing PD."
      explanation: >-
        Review reporting general agreement that pesticide exposure affects the
        probability of developing the disease. It establishes the exposure at
        the level of the disease and says nothing about mitochondria.
  - target: Nigral Cellular Senescence
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Paraquat is the one compound in this entry with a measured senescence mechanism. It induces
      senescence and a secretory phenotype in astrocytes in culture and in mouse brain, and
      clearing the senescent cells it generates protects the nigral dopaminergic population. The
      human arm of this exposure is the epidemiological association only; the senescence mechanism
      is mouse and cell-culture work.
    evidence:
    - reference: PMID:29386135
      reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
      supports: SUPPORT
      directness: DIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Additionally, PQ was found to induce astrocytic senescence and an SASP in vitro and in vivo, and senescent cell depletion in the latter protects against PQ-induced neuropathology."
      explanation: >-
        Names the exposure, the astrocytic senescence this edge asserts, and the depletion
        experiment showing the senescent cells matter for the resulting neuropathology. Cell
        culture and mouse, so the mechanism is not established for human paraquat exposure.
    - reference: PMID:29386135
      reference_title: "Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Similar to astrocytes in human PD tissues, astrocytes from PQ-treated mice also displayed significant loss of nuclear lamin B1 and HMGB1 (high mobility group box 1), the latter necessary for SASP initiation"
      explanation: >-
        The marker comparison tying the exposure model to the human tissue finding: paraquat
        reproduces in mouse astrocytes the lamin B1 and HMGB1 loss seen in parkinsonian nigral
        astrocytes. Indirect, because matching markers in a toxicant model is not evidence that
        paraquat caused the human changes.
  notes: >-
    Rotenone and paraquat are the compounds with the longest-standing link to the disease,
    but they are a small part of the implicated set: the PEG screen associates 53 active
    ingredients at FDR 0.05 or below, and 18 of its top 25 remain registered with the US EPA.
    Treat the per-compound estimates as a ranking of candidates rather than a list of
    established causes, and do not read the odds ratios as comparable potencies: each is per
    one standard deviation of its own compound's exposure distribution, so the column is
    denominated differently on every row. Note also that the paper's top five is ordered by
    FDR, not by odds ratio, and the two orderings differ. The largest odds ratio in the
    deposited Fig. 2b table, fluazifop-butyl at 1.260, ranks 32nd of 68 by p and is absent
    from the top five, because it also carries the table's widest confidence interval,
    1.090-1.456. That is an outlier rather than the pattern: the other seven compounds in the
    top eight by odds ratio all sit within 6% of the median interval width and all rank in
    the top nine by p. Quote the paper's ordering rather than re-ranking by odds ratio. The
    same screen shows the exposures are heavily correlated, with 75%
    of the associated pesticides that either were not individually toxic to neurons or could
    not be tested correlating at R 0.45 or above with at least one that was, and none of the
    per-compound models adjust for the others. Dicofol is the most interconnected compound in
    that correlation network, followed by propargite and methomyl.

    Two points about the golf-course proximity study (PMID:40338549) that its own Results
    prose does not make plain. Table 3 uses "vulnerable groundwater with a golf course" as
    its reference, so the golf-course contrast within vulnerable groundwater regions has to
    be recovered by inverting the vulnerable-without-a-course row, 0.74 (0.43-1.27), giving
    1.35 (0.79-2.33) at p = 0.28. That contrast is null and the paper does not report it.
    The paper's claim that the largest effect sizes were for a golf course in a vulnerable
    groundwater region rests instead on comparisons against nonvulnerable strata, 1.82
    (1.09-3.03) and 1.92 (1.06-3.45), both of which reproduce exactly on inversion; the
    sentence reporting the second describes its comparator only as service areas without a
    golf course, omitting that the row is the nonvulnerable one. Quote that paper's own
    comparisons with their comparators named. Separately, searches of PubMed for golf-course
    exposure and parkinsonism, and for golf-course pesticide work generally, found no study
    reproducing the proximity association outside this cohort: the only other human report
    is an anecdotal letter describing 19 of 26 patients living within 2 miles of a course
    (PMID:23280848). Treat the association as unreplicated on the evidence located so far
    rather than as absent from the literature.

    The compound-level evidence is uneven. Paraquat and rotenone carry the
    strongest and most consistent associations; organochlorines are positive on
    blood-measured exposure but heterogeneous by region; and the association for
    several compounds depends on whether protective equipment was used, which is
    evidence that the exposure rather than the farming lifestyle is what
    matters. Manganese is deliberately not curated here: the metals
    meta-analysis found no association between manganese and idiopathic
    Parkinson disease, and manganism is a distinct toxicant parkinsonism rather
    than a synucleinopathy.
  evidence:
  - reference: PMID:15177059
    reference_title: "Occupational and environmental risk factors for Parkinson's disease."
    supports: SUPPORT
    snippet: "there is general agreement that smoking and exposure to pesticides affect the probability of developing PD."
    explanation: This review supports pesticide exposure as an environmental factor influencing PD risk.
  - reference: PMID:37193692
    reference_title: "A pesticide and iPSC dopaminergic neuron screen identifies and classifies Parkinson-relevant pesticides."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our PWAS implicated 25 pesticides as associated with PD at a meta-analysis FDR ≤ 0.01 (8.7% of all tested pesticides), another 28 at 0.01<FDR ≤ 0.05 (9.7%), and 15 at 0.05<FDR < 0.10 (5.2%)"
    explanation: >-
      Record-based pesticide-wide association study in PEG, 829 patients and 824 controls in
      three agricultural counties of central California, testing the 288 active ingredients
      with at least 25 exposed participants. Exposure came from California Pesticide Use
      Report application records combined with land-use maps in a GIS model, not from
      self-report. The per-compound odds ratios this screen reports are per one standard
      deviation of the log-transformed, centred and SD-scaled exposure estimate, pooled
      across two study waves and two locations by fixed-effects meta-analysis; they are not
      ever-versus-never contrasts, so the unit has to travel with any quoted figure. Each
      pesticide's estimate is scaled to its own standard deviation and no per-compound
      standard deviations are published, so an odds ratio here cannot be converted back to
      pounds per acre per year, and two compounds' odds ratios are not on a common scale.
      Models were adjusted for age, sex, race/ethnicity, education and index year, and not
      for smoking or for co-exposure to the correlated pesticides the same paper maps.
  - reference: PMID:32919961
    reference_title: "Pesticide use and incident Parkinson's disease in a cohort of farmers and their spouses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ever-use of the insecticide terbufos (HR:1.31, 95%CI:1.02-1.68) and the herbicides trifluralin (HR:1.29, 95%CI: 0.99-1.70) and 2,4,5-T (HR:1.57, 95%CI:1.21-2.04) was associated with elevated PD risk."
    explanation: >-
      Agricultural Health Study, a prospective cohort independent of PEG: 38,274 pesticide
      applicators and 27,836 spouses followed about 20 years, with covariate-adjusted Cox
      regression on self-reported ever-use of 50 named pesticides, with 491 incident cases.
      It implicates specific compounds rather than pesticides as a class, and reaches that
      from a different exposure design than the record-based PEG estimates. The trifluralin
      interval includes 1.0, so that compound is an elevated point estimate the authors count
      among their positive findings rather than a conventionally significant result; its
      weight comes from the independence of the design, not from the interval. The same paper
      reports higher risk among participants with a history of head injury, which bears on
      the Head Trauma factor in this entry.
  - reference: PMID:40338549
    reference_title: "Proximity to Golf Courses and Risk of Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "living within 1 mile of a golf course was associated with 126% increased odds of PD compared with those living farther than 6 miles away from a golf course (aOR, 2.26; 95% CI, 1.09-4.70)"
    explanation: >-
      Population-based case-control study in the Rochester Epidemiology Project: 419
      incident cases from Olmsted County, Minnesota, 1991 to 2015, each diagnosis confirmed
      by a movement disorder specialist, matched 20:1 to 5113 controls. It adds a third
      exposure design to this factor, alongside the PEG application-record model and the
      Agricultural Health Study's self-reported use, and like PEG it is a proximity model
      rather than a measurement of uptake: exposure is the distance from a home address, 2
      to 3 years before symptom onset, to the digitised boundary of the nearest of 139 golf
      courses. No pesticide was measured in water, air or any participant, and the paper
      identifies no compound, so it supports pesticide exposure as a factor only through
      the authors' inference that courses are treated with pesticides. Read the odds ratios
      as a gradient rather than as potencies, and note that most of the unadjusted signal is
      geography: the same two contrasts are 7.23 and 12.38 before adjustment and 2.26 and
      2.98 after it, 80.4% of cases were urban against 30.5% of controls, and median
      pre-index healthcare utilisation was 8.4 days per year in cases against 0.6 in
      controls. The quoted figure is the fully adjusted estimate. A sensitivity analysis
      restricted to Olmsted County controls is reported as consistent, which is the check
      that matters most given that cases had to live in that county at onset while controls
      came from all 27.
  - reference: PMID:30474499
    reference_title: "Paraquat exposure and Parkinson's disease: A systematic review and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A subsequent meta-analysis showed an association between PD and paraquat exposure (odds ratio = 1.64 (95% CI: 1.27-2.13; I2 = 24.8%)"
    explanation: >-
      Meta-analysis of 13 case-control studies giving the paraquat-specific odds
      ratio with low heterogeneity. Note that this paper carries a published
      erratum (Arch Environ Occup Health 2019;74(5):292-293).
  - reference: PMID:39520734
    reference_title: "Environmental and occupational exposure to organochlorine pesticides associated with Parkinson's disease risk: A systematic review and meta-analysis based on epidemiological evidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The results showed that OCPs exposure increased PD risk, including seven blood sample assessment exposure (BOCPs) studies (OR = 1.54, 95 % CI = 1.32-1.79) and 10 indirect assessment exposure (IOCPs) studies (OR = 1.19, 95 % CI = 1.04-1.35)"
    explanation: >-
      The organochlorine association is stronger when exposure is measured in
      blood than when it is inferred, which is the direction expected if the
      association is real rather than a product of recall. The same paper
      reports the association as positive in Asia and not significant in North
      America or Europe, so the pooled figure should not be read as uniform.
  - reference: PMID:25461423
    reference_title: "Protective glove use and hygiene habits modify the associations of specific pesticides with Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Rotenone was associated with PD regardless of glove use."
    explanation: >-
      In this study the paraquat and permethrin associations were confined to
      people who did not use gloves, while the rotenone association persisted in
      both groups. A dose-modifying effect of protective equipment is evidence
      that the chemical exposure itself is doing the work.
- name: Trifluralin Exposure
  exposure_term:
    preferred_term: exposure to trifluralin
    term:
      id: ECTO:9000644
      label: exposure to trifluralin
  disease_effect: PREDISPOSES
  causal_role: RISK_FACTOR
  description: >-
    Trifluralin is a dinitroaniline herbicide, still registered in the United States, that
    carries its own entry because it is the one compound from the PEG screen taken through to
    a measured lesion in human cells. A human induced-pluripotent-stem-cell midbrain
    dopaminergic culture shows where it acts: a dose-dependent loss of reserve respiratory
    capacity with basal ATP output held, alongside preferential loss of complex I and complex
    IV subunits. Two cohorts with different exposure designs, PEG and the Agricultural Health
    Study, put the exposure in the same direction, but the Agricultural Health Study interval
    includes no effect, so the epidemiology is consistent rather than settled. The cell work
    is also acute and high-dose against a chronic low-dose human exposure, so neither layer
    establishes the other on its own.
  chemicals:
  - trifluralin
  exposure_classifications:
    hazard_agent_type:
    - classification_value: CHEMICAL
    exposure_route:
    - classification_value: UNKNOWN
      notes: As for Pesticide Exposure, neither cited cohort resolves the route of uptake.
    exposure_duration:
    - classification_value: CHRONIC
      notes: >-
        Chronic in both cohorts: PEG averaged ambient estimates over a window of roughly two
        decades, and the Agricultural Health Study scored ever-use across a working life. The
        experiments that establish the mechanism are not chronic. The blots are a single
        24-hour exposure at 30 µM and the respirometry is 6 hours at 30-90 µM, doses the
        authors describe as chosen as "higher concentrations for shorter times rather than
        years worth of lower-level exposure".
    exposome_domain:
    - classification_value: SPECIFIC_EXTERNAL
  influences_mechanisms:
  - target: Mitochondrial Dysfunction
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Trifluralin removes the respiratory reserve of human dopaminergic neurons without
      lowering their resting ATP output, and depletes complex I and complex IV subunits more
      than the other three complexes. This is a narrower claim than the rat rotenone work
      that otherwise carries this node, and it is made in human cells, but it is an acute
      high-dose exposure and so does not by itself establish the lesion as the consequence of
      chronic agricultural exposure. The route into alpha-synuclein is deliberately not
      claimed: two weeks of a sublethal dose produced no change in phosphorylated
      alpha-synuclein, recorded below as a refutation.
    evidence:
    - reference: PMID:37193692
      reference_title: "A pesticide and iPSC dopaminergic neuron screen identifies and classifies Parkinson-relevant pesticides."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "We measured mitochondrial subunit abundance after 24 h exposure to 30 µM trifluralin in 3 biological replicates and demonstrated a 50% reduction of Complex I (NDUFB8) and Complex IV (COX II) when compared to DMSO treated controls"
      explanation: >-
        Western blot in SNCA-triplication iPSC-derived midbrain dopaminergic neurons, 30 µM
        for 24 hours, n=3. The deposited source data give complex I at 49.1% and complex IV
        at 57.4% of control, so the stated 50% reduction is accurate for complex I and
        generous for complex IV. The claim recorded here is preferential loss rather than
        sparing of the rest: the deposited values also fall for SDHB (65.5%), ATP5A (81.6%),
        UQCRC2 (87.2%) and SDHA (88.7%), and every one of the six falls in all three
        replicates. The paper's statement that the other complexes show no significant change
        is a statement about significance at n=3, not an absence of effect.
    - reference: PMID:37193692
      reference_title: "A pesticide and iPSC dopaminergic neuron screen identifies and classifies Parkinson-relevant pesticides."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The respiratory capacity of differentiated neurons was reduced to 9% when cells were treated with trifluralin at 90 µM, 26% at 60 µM, and 72% at 30 µM trifluralin compared to DMSO control, with the highest two doses being significantly different from DMSO control"
      explanation: >-
        Mito Stress respirometry, 6 hours, n=3. These are spare respiratory capacity as a
        percentage of DMSO control, so 90 µM is a reduction of about 91%, not to a 9%
        reduction. The quoted figures are means of the per-replicate ratios; aggregating as a
        ratio of means instead gives 9.4%, 25.9% and 74.0%, which is why a recomputation from
        the deposited data does not land exactly on the published numbers. The specific point
        for this node is the dissociation: across the same doses ATP production ran at 112.9%,
        113.1% and 103.9% of control, so reserve capacity collapsed while resting output was
        maintained or slightly raised. Only the 60 and 90 µM reductions are significant.
    - reference: PMID:31973855
      reference_title: "Do trifluralin and tebuthiuron impair isolated rat liver mitochondria?"
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "trifluralin can disturb the mitochondrial respiration, especially at the highest concentration, but it cannot induce oxidative stress"
      explanation: >-
        Independent group, and a different species, tissue and preparation: mitochondria
        isolated from rat liver and then dosed in suspension, so this is a biochemical assay
        outside an organism rather than animal exposure. It supports the respiratory half of
        this link in a second system, and it matters for the node this entry conforms to: the
        node bundles complex I inhibition with oxidative stress, and here a group that assayed
        oxidative stress from trifluralin reports not finding it. Paul et al. assayed no
        reactive oxygen species in the dopaminergic neurons, so neither study leaves an
        oxidative-stress claim standing for this compound.
    - reference: PMID:37193692
      reference_title: "A pesticide and iPSC dopaminergic neuron screen identifies and classifies Parkinson-relevant pesticides."
      supports: REFUTE
      evidence_source: IN_VITRO
      snippet: "Western blot revealed very low levels of pS129 expression in both control and trifluralin treated conditions and no significant difference in pS129 was detected"
      explanation: >-
        Two weeks at a sublethal 6 µM, which is why no alpha-synuclein route is claimed for
        this compound. The negative is weaker than it looks against the positive findings,
        because those come from 30-90 µM over 6 to 24 hours: a null at a twentieth of the
        dose does not exclude an effect at the doses where the mitochondrial lesion appears.
        The authors cite trifluralin promoting alpha-synuclein fibril formation in a cell-free
        system; no independent source names trifluralin as a fibril promoter, so that
        attribution is not carried here.
  notes: >-
    The dose and duration of each experiment are stated in the evidence explanations because
    EvidenceItem has no slot for them; see issue #15581. The co-exposure result from the same
    paper, in which trifluralin with tribufos at 10 µM produced a 65% decrease in neuron
    count against 32% and 8% for the compounds alone, is not recorded as a separate claim:
    the combination arm ran 6 to 7 wells per combination against 117 control wells, and one
    pair in the same matrix came out less toxic than trifluralin alone.
  evidence:
  - reference: PMID:32919961
    reference_title: "Pesticide use and incident Parkinson's disease in a cohort of farmers and their spouses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ever-use of the insecticide terbufos (HR:1.31, 95%CI:1.02-1.68) and the herbicides trifluralin (HR:1.29, 95%CI: 0.99-1.70) and 2,4,5-T (HR:1.57, 95%CI:1.21-2.04) was associated with elevated PD risk."
    explanation: >-
      Agricultural Health Study, 38,274 applicators and 27,836 spouses, about 20 years of
      follow-up, 491 incident cases, covariate-adjusted Cox regression on self-reported
      ever-use. The interval on the hazard ratio of 1.29 includes 1.0, so this is an elevated
      point estimate the authors count among their positive findings, not a conventionally
      significant result, and it should not be cited as a cohort confirming trifluralin
      without the interval. What it does carry is independence: disjoint authors from the PEG
      group, self-reported ever-use rather than a GIS exposure model, and different outcome
      ascertainment, all pointing the same direction. It is also the prior association the
      source paper gives as its reason for following this compound.
  - reference: PMID:37193692
    reference_title: "A pesticide and iPSC dopaminergic neuron screen identifies and classifies Parkinson-relevant pesticides."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Ten PWAS pesticides led to cell death >3 standard deviations above the DMSO control mean at a concentration of 30 µM: propargite, copper sulfate (basic and pentahydrate), dicofol, folpet, naled, endothall, trifluralin, endosulfan, and diquat dibromide"
    explanation: >-
      Live count of TH-tdTomato-positive neurons at day 11 in iPSC-derived midbrain
      dopaminergic cultures, screening 39 of the PWAS-associated pesticides over a four-point
      dose curve. Trifluralin is one of the ten entries, all of which were also toxic at 6 µM.
      Two controls bound how far this goes: five of the ten showed no substantial toxicity in
      a cardiomyocyte counter-screen, which is the argument for dopaminergic selectivity, and
      the hits reproduced in a line with SNCA corrected to two wild-type copies, so the
      toxicity does not depend on an alpha-synuclein background.
- name: Chlorpyrifos Exposure
  exposure_term:
    preferred_term: exposure to chlorpyrifos
    term:
      id: ECTO:9000633
      label: exposure to chlorpyrifos
  influences_mechanisms:
  - target: Autophagy-Lysosome Pathway Dysfunction
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Chlorpyrifos is the one implicated pesticide whose experimental mechanism
      is reported as autophagic rather than mitochondrial. In zebrafish the
      dopaminergic loss it causes is attributed to impaired autophagic flux
      together with synuclein accumulation, and is reversed by restoring flux or
      by removing synuclein. The human arm of the same study is a residential
      exposure association and does not measure autophagy, so the mechanism is
      carried by the animal and cell work alone.
    evidence:
    - reference: PMID:41382278
      reference_title: "The pesticide chlorpyrifos increases the risk of Parkinson's disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Using ZF, we found that CPF-induced dopaminergic neuron loss was at least partially due to autophagy dysfunction and synuclein accumulation, as knocking down LC3 recapitulated the dopaminergic neuron loss and restoring autophagic flux or eliminating synuclein reduced neuronal vulnerability."
      explanation: >-
        The rescue experiments are what make this an autophagy claim rather than
        a correlation: restoring flux reduces the loss, and knocking down LC3
        reproduces it. Zebrafish work, so it establishes the route in the model
        and not in human disease.
  notes: >-
    Curated separately from the general pesticide entry because its reported
    mechanism is distinct. The human exposure assessment is long-term
    residential proximity, not occupational handling.
  evidence:
  - reference: PMID:41382278
    reference_title: "The pesticide chlorpyrifos increases the risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RESULTS: Long-term residential exposure to CPF was associated with more than a 2.5-fold increased risk of developing PD."
    explanation: >-
      The human arm of the study, a case-control analysis of 829 patients and
      824 controls, gives the residential exposure association.
- name: Trichloroethylene Exposure
  exposure_term:
    preferred_term: exposure to trichloroethene
    term:
      id: ECTO:9000530
      label: exposure to trichloroethene
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Service at a base whose water supply carried trichloroethylene at many
      times the permissible concentration is followed by a raised risk of the
      disease decades later. Pointed at the core lesion rather than at a
      mechanism node because the cohort study measures incidence only and no
      cited sentence follows the solvent to any particular step. The same study
      found no excess of other parkinsonian syndromes, which argues the
      association is specific to this disease rather than to parkinsonism
      generally.
    evidence:
    - reference: PMID:37184848
      reference_title: Risk of Parkinson Disease Among Service Members at Marine Corps Base Camp Lejeune.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In multivariable models, Camp Lejeune veterans had a 70% higher risk of PD (odds ratio, 1.70; 95% CI, 1.39-2.07; P < .001)."
      explanation: >-
        Cohort of 158,122 veterans with exposure data and 430 cases. It
        quantifies the exposure-disease association and not the neuronal loss
        this link targets.
  evidence:
  - reference: PMID:37184848
    reference_title: Risk of Parkinson Disease Among Service Members at Marine Corps Base Camp Lejeune.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No excess risk was found for other forms of neurodegenerative parkinsonism."
    explanation: >-
      The negative result for other parkinsonian syndromes in the same cohort.
      It is the reason this exposure is curated on this entry and not on the
      multiple system atrophy or dementia with Lewy bodies entries.
- name: Ambient Fine Particulate Matter
  exposure_term:
    preferred_term: exposure to PM2.5 in ambient air
    term:
      id: ECTO:7000117
      label: exposure to fine respirable suspended particulate matter
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      A small increase in incidence per increment of fine particulate matter in
      a large population cohort. Pointed at the core lesion rather than at
      neuroinflammation, which is the usual proposal and which this entry holds
      a node for, because the cohort study measures incidence and nothing in it
      measures an inflammatory route. The effect is small and its lower
      confidence bound is close to unity, so it should not be read as a strong
      risk factor.
    evidence:
    - reference: PMID:30124852
      reference_title: "Effects of ambient air pollution on incident Parkinson's disease in Ontario, 2001 to 2013: a population-based cohort study."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Each interquartile increment (3.8 µg/m3) of PM2.5 was associated with a 4% increase in incident PD (95% confidence interval, 1.01-1.08) after adjusting for various covariates."
      explanation: >-
        Population cohort of about 2.2 million adults with 38,745 incident
        cases. It gives the exposure-incidence association; the interval's lower
        bound of 1.01 is the reason the description declines to call this strong.
  notes: >-
    The study also reported associations for nitrogen dioxide and for ozone,
    which are separate pollutants rather than size fractions of this one and are
    not curated here.
  evidence:
  - reference: PMID:30124852
    reference_title: "Effects of ambient air pollution on incident Parkinson's disease in Ontario, 2001 to 2013: a population-based cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Each interquartile increment (3.8 µg/m3) of PM2.5 was associated with a 4% increase in incident PD (95% confidence interval, 1.01-1.08) after adjusting for various covariates."
    explanation: The cohort association between fine particulate matter and incident disease.
- name: Lead Exposure
  exposure_term:
    preferred_term: exposure to lead
    term:
      id: ECTO:9000945
      label: exposure to lead
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cumulative lead measured in bone, which indexes lifetime rather than
      recent exposure, is associated with raised risk. Pointed at the core
      lesion because the meta-analysis measures risk and not any mechanistic
      step. Lead is the only metal this meta-analysis found positive.
    evidence:
    - reference: PMID:37022311
      reference_title: "Metal Exposure and Risk of Parkinson Disease: A Systematic Review and Meta-Analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Cumulative lead levels in bone were found to be associated with increased risk of PD."
      explanation: >-
        Meta-analysis of 83 case-control and 5 cohort studies. Bone lead is a
        cumulative measure, which matters because a blood measurement taken
        after diagnosis could reflect the disease rather than precede it.
  notes: >-
    Recorded here partly for what it rules out. The same meta-analysis found no
    association for the other metals it examined, and reported copper, iron and
    zinc as lower in cases than controls, which is more readily explained as a
    consequence of the disease than as a cause of it. Manganese was null for
    idiopathic Parkinson disease, so manganese parkinsonism is not curated on
    this entry.
  evidence:
  - reference: PMID:37022311
    reference_title: "Metal Exposure and Risk of Parkinson Disease: A Systematic Review and Meta-Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We did not find associations between other metals and PD."
    explanation: >-
      The null result for metals other than lead. Curated as evidence in its own
      right so the entry distinguishes a metal that was studied and found null
      from one that was never studied.
- name: Dairy Consumption
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      High dairy and milk intake is associated with a modestly raised risk in
      pooled prospective cohorts, with a dose gradient per cup of milk per day
      and a stronger association in men. Pointed at the core lesion because the
      meta-analysis is dietary epidemiology with no mechanistic arm. Dairy is
      often discussed as a vehicle for pesticide residues or as acting through
      urate, but nothing cited here measures either route.
    evidence:
    - reference: PMID:41252180
      reference_title: "Foods and Dietary Intakes and the Risk of Parkinson's Disease: A Systematic Review and Dose-Response Meta-analysis of Prospective Cohort Studies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "High consumption of dairy, low-fat dairy, and milk demonstrated 26% (odd ratio [OR], 1.26; 95% CI, 1.12-1.41), 30% (OR, 1.30; 95% CI, 1.06-1.58), and 23% (OR, 1.23; 95% CI, 1.07-1.43) increased PD risk compared with the lowest intake categories, respectively."
      explanation: >-
        Meta-analysis of 29 prospective cohorts totalling 1,307,337
        participants. Prospective design addresses the reverse-causation
        objection that weakens case-control dietary studies.
  notes: >-
    Left unbound because ECTO has no class at the level this finding is
    reported. Searched the EBI Ontology Lookup Service for dairy, milk, cheese
    and yogurt: every ECTO exposure class returned is a specific product, and
    the milk and cheese and yogurt children are graded by fat content, so
    binding one of them would assert a fat stratum. That stratum is the thing
    this meta-analysis specifically does not single out, since it reports raised
    risk for low-fat dairy as well as for dairy overall. The only term carrying
    the word dairy is exposure to dairy-based coffee drink via ingestion, which
    is a different exposure. The same meta-analysis found legumes and nuts
    protective.
  evidence:
  - reference: PMID:41252180
    reference_title: "Foods and Dietary Intakes and the Risk of Parkinson's Disease: A Systematic Review and Dose-Response Meta-analysis of Prospective Cohort Studies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "High consumption of dairy, low-fat dairy, and milk demonstrated 26% (odd ratio [OR], 1.26; 95% CI, 1.12-1.41), 30% (OR, 1.30; 95% CI, 1.06-1.58), and 23% (OR, 1.23; 95% CI, 1.07-1.43) increased PD risk compared with the lowest intake categories, respectively."
    explanation: The pooled prospective association between dairy intake and disease risk.
- name: Helicobacter pylori Infection
  exposure_term:
    preferred_term: exposure to Helicobacter pylori
    term:
      id: ECTO:3000003
      label: exposure to Helicobacter pylori
  influences_mechanisms:
  - target: Intestinal Inflammation and Barrier Dysfunction
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Gastric infection with Helicobacter pylori is the strongest of the
      infectious associations in the pooled analysis. Pointed at intestinal
      inflammation and barrier dysfunction as the node the exposure plausibly
      acts through, with the intermediates left unknown because the
      meta-analysis is seroprevalence and risk and measures no mucosal or
      barrier endpoint. The direction of causation is not settled by these data:
      gastrointestinal dysfunction is itself an early feature of the disease.
    evidence:
    - reference: PMID:32017453
      reference_title: "Bacterial, viral, and fungal infection-related risk of Parkinson's disease: Meta-analysis of cohort and case-control studies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Helicobacter pylori (HP; pooled OR = 1.653, 1.426-1.915, p < .001), hepatitis C virus (HCV; pooled OR = 1.195, 1.012-1.410, p = .035), Malassezia (pooled OR = 1.694, 1.367-2.100, p < .001), and pneumoniae (pooled OR = 1.595, 1.020-2.493, p = .041) infection were associated with increased PD risk."
      explanation: >-
        Meta-analysis of 23 studies. It gives the infection-disease association
        and does not measure the intestinal barrier this link targets.
  notes: >-
    Recorded with its nulls, which are the more informative half of this
    literature: the same meta-analysis tested a long list of common infections
    and found them unrelated to risk, so the positive findings are not a general
    effect of having been infected with something.
  evidence:
  - reference: PMID:32017453
    reference_title: "Bacterial, viral, and fungal infection-related risk of Parkinson's disease: Meta-analysis of cohort and case-control studies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Influenza virus, herpes virus, hepatitis B virus, scarlet fever, mumps virus, chicken pox, pertussis, German measles, and measles were not associated with PD risk."
    explanation: >-
      The null results for nine common infections, curated so the entry
      distinguishes infections that were studied and found unrelated from
      infections nobody has examined. Influenza in particular has a long
      history of being proposed as a cause of parkinsonism.
- name: Hepatitis C Virus Infection
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Chronic hepatitis C infection carries a modestly raised risk in the same
      pooled analysis that reports the Helicobacter pylori association, and the
      interval's lower bound is close to unity, so the association is weak taken
      on its own. What makes it worth curating separately is the treatment arm:
      risk was lower among infected patients who received antiviral treatment
      than among those who did not, which is the closest thing in this
      literature to removing the exposure and watching the risk fall. Pointed at
      the core lesion rather than at neuroinflammation, which is the usual
      proposal for a systemic viral route and which this entry holds a node for,
      because nothing in the meta-analysis measures an inflammatory or central
      endpoint.
    evidence:
    - reference: PMID:32017453
      reference_title: "Bacterial, viral, and fungal infection-related risk of Parkinson's disease: Meta-analysis of cohort and case-control studies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Helicobacter pylori (HP; pooled OR = 1.653, 1.426-1.915, p < .001), hepatitis C virus (HCV; pooled OR = 1.195, 1.012-1.410, p = .035), Malassezia (pooled OR = 1.694, 1.367-2.100, p < .001), and pneumoniae (pooled OR = 1.595, 1.020-2.493, p = .041) infection were associated with increased PD risk."
      explanation: >-
        The hepatitis C odds ratio, quoted in the sentence that carries all four
        positive infection results because they share one clause. Its lower
        bound of 1.012 is why the description declines to call this strong.
    - reference: PMID:32017453
      reference_title: "Bacterial, viral, and fungal infection-related risk of Parkinson's disease: Meta-analysis of cohort and case-control studies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "After antiviral treatment against HCV reduced the risk of PD in patients with HCV infection (OR = 0.672, 0.571-0.791, p < .001)."
      explanation: >-
        The treatment arm, which bears on direction of causation in a way the
        prevalence comparison cannot: treated and untreated patients are both
        infected, so the contrast is not between infected and uninfected people.
        It is still observational, and patients selected for antiviral treatment
        differ from those who are not.
  notes: >-
    Left unbound. The only hepatitis C class in ECTO is exposure to Hepatitis C
    virus HCV-476, which names a single isolate, and the EBI Ontology Lookup
    Service returns no generic hepatitis C or hepacivirus exposure class, so
    binding it would assert a strain that the meta-analysis does not
    distinguish. Searched for hepatitis; the other hits are hepatitis B and
    hepatitis E, and hepatitis B is null for this disease, which is curated
    beside the Helicobacter pylori record above. Exposure to virus,
    ECTO:3000001, is a true parent and is already bound elsewhere in this
    knowledge base, but it names no organism and so would ground the record at a
    level that distinguishes nothing; the Helicobacter pylori record beside this
    one carries a species-level term, and an unbound record is a smaller loss
    than an inconsistent pair.
  evidence:
  - reference: PMID:32017453
    reference_title: "Bacterial, viral, and fungal infection-related risk of Parkinson's disease: Meta-analysis of cohort and case-control studies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CONCLUSION: Patients with infection of HP, HCV, Malassezia, pneumoniae might be an increased risk of PD. Antiviral treatment of HCV could reduce the risk of PD."
    explanation: >-
      The authors' own summary, which states both the association and the
      treatment effect that this entry curates as separate evidence items.
- name: Truncal Vagotomy
  influences_mechanisms:
  - target: Vagal-Brainstem Alpha-Synuclein Propagation
    environmental_effect: PROTECTS_AGAINST
    causal_link_type: DIRECT
    description: >-
      Surgically cutting the vagal trunk is the closest thing in the human
      literature to an experimental test of vagal propagation, because it
      interrupts exactly the anatomical route this node describes. Risk after
      full truncal vagotomy was lower than in the general population at more
      than twenty years of follow-up, while selective vagotomy, which spares the
      trunk, showed no such reduction. The contrast between the two operations is
      what makes this informative about the route rather than about surgery.
    evidence:
    - reference: PMID:26031848
      reference_title: "Vagotomy and subsequent risk of Parkinson's disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Risk of PD was also decreased after truncal vagotomy when compared to the general population cohort (overall adjusted HR = 0.85; 95% CI: 0.63-1.14; follow-up >20 years, adjusted HR = 0.53; 95% CI: 0.28-0.99)."
      explanation: >-
        Danish registry cohort. The headline protective figure is the
        twenty-year subgroup and its interval only just excludes unity; the
        overall estimate includes it. The authors state the precision limit
        themselves, which is why this link is curated as suggestive rather than
        established.
    - reference: PMID:26031848
      reference_title: "Vagotomy and subsequent risk of Parkinson's disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In patients who underwent superselective vagotomy, risk of PD was similar to the general population (HR = 1.09; 95% CI: 0.84-1.43; follow-up of >20 years: HR = 1.16; 95% CI: 0.80-1.70)."
      explanation: >-
        The comparison operation. Selective vagotomy leaves the vagal trunk
        intact and carries no risk reduction, which is the control that makes
        the truncal result bear on the propagation route specifically.
  notes: >-
    No ECTO term binds this exposure. Searched the committed ECTO cache and the
    EBI Ontology Lookup Service for vagotomy, vagus, vagal and surgical
    denervation, and none of those queries returned an exposure class; the
    nearest concepts in ECTO are chemical and environmental agents rather than
    surgical procedures, so the entry is deliberately left unbound rather than
    forced onto a broader term.
  evidence:
  - reference: PMID:26031848
    reference_title: "Vagotomy and subsequent risk of Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Statistical precision of risk estimates was limited."
    explanation: >-
      The authors' own statement of the study's main limitation, quoted so the
      entry does not present the twenty-year hazard ratio as a firm result.
- name: Cigarette Smoking
  exposure_term:
    preferred_term: exposure to cigarette smoking
    term:
      id: ECTO:0100003
      label: exposure to cigarette smoking
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PROTECTS_AGAINST
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The inverse association between smoking and this disease is among the most
      reproducible findings in its epidemiology, and is reported with a
      dose-response relationship. Pointed at the core lesion because the pooled
      analysis measures risk and no cited sentence follows nicotine to any
      mechanistic step. Whether the association is protective at all remains
      disputed: reverse causation, in which a prodromal personality change makes
      people less likely to take up or continue smoking, is the standing
      alternative explanation and is not excluded by these data.
    evidence:
    - reference: PMID:26272284
      reference_title: "Association between cigarette smoking and Parkinson's disease: A meta-analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The pooled RR of PD was 0.59 (95% CI, 0.56-0.62) for ever smokers compared with never smokers."
      explanation: >-
        Meta-analysis of 61 case-control and 8 cohort studies. It gives the
        inverse association and does not establish a protective mechanism.
  notes: >-
    Curated as a protective association rather than a protective mechanism. The
    effect direction reverses in isolated REM sleep behaviour disorder, where
    smoking is a risk factor, and is null in dementia with Lewy bodies; those
    results are curated on their own entries and are the reason this exposure
    must not be propagated across the synucleinopathies.
  evidence:
  - reference: PMID:26272284
    reference_title: "Association between cigarette smoking and Parkinson's disease: A meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The pooled RR of PD was 0.59 (95% CI, 0.56-0.62) for ever smokers compared with never smokers."
    explanation: The pooled inverse association between ever having smoked and the disease.
- name: Caffeine Consumption
  exposure_term:
    preferred_term: exposure to caffeine
    term:
      id: ECTO:9000205
      label: exposure to caffeine
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PROTECTS_AGAINST
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Regular caffeine intake is associated with lower incidence in prospective
      follow-up of healthy cohorts. Pointed at the core lesion because the
      pooled analysis measures incidence; adenosine A2A receptor antagonism is
      the usual proposed route and nothing cited here measures it. As with
      smoking, reverse causation is a live objection, since reduced caffeine
      intake can itself be a prodromal feature.
    evidence:
    - reference: PMID:32580456
      reference_title: "The Effect of Caffeine on the Risk and Progression of Parkinson's Disease: A Meta-Analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The individuals in the healthy cohort with regular caffeine consumption had a significantly lower risk of PD during follow-up evaluation (hazard ratio (HR) = 0.797, 95% CI = 0.748-0.849, p < 0.001)."
      explanation: >-
        Meta-analysis of 13 studies. The estimate is taken from the healthy
        cohort arm, which is the one that bears on incidence rather than on
        progression in established disease.
  evidence:
  - reference: PMID:32580456
    reference_title: "The Effect of Caffeine on the Risk and Progression of Parkinson's Disease: A Meta-Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The individuals in the healthy cohort with regular caffeine consumption had a significantly lower risk of PD during follow-up evaluation (hazard ratio (HR) = 0.797, 95% CI = 0.748-0.849, p < 0.001)."
    explanation: The prospective inverse association between regular caffeine intake and incidence.
- name: Rural Living
  notes: >-
    Left without a mechanism link deliberately. Rural living, well-water
    drinking and farming are proxies for an unidentified exposure rather than
    exposures in their own right, and the most careful assessment of this
    literature concludes that the quantitative support for them is inconsistent
    even though the pesticide associations they are supposed to stand for are
    not. Linking a proxy to a mechanism node would assert a route that the
    cited work explicitly declines to support. No ECTO term binds this exposure
    either. Searched the EBI Ontology Lookup Service for rural, well water,
    farming and agricultural, and none returned a class covering residence:
    exposure to farm, which this work added for isolated REM sleep behaviour
    disorder, names an occupational setting and is narrower than the
    rural-living and well-water composite this record describes.
  evidence:
  - reference: PMID:11437458
    reference_title: "Environmental risk factors and Parkinson's disease: a metaanalysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings suggest that living in a rural area, drinking well water, farming, and exposure to pesticides may be a risk factor for developing PD."
    explanation: >-
      The classic meta-analysis that established these composite proxies as
      candidate risk factors.
  - reference: PMID:27055126
    reference_title: "Association between Parkinson's Disease and Cigarette Smoking, Rural Living, Well-Water Consumption, Farming and Pesticide Use: Systematic Review and Meta-Analysis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast, associations between PD and rural living, well-water consumption, farming and the use of pesticides, herbicides, insecticides, fungicides or paraquat were less consistent when assessed quantitatively or qualitatively."
    explanation: >-
      A weight-of-evidence assessment that used the smoking association as a
      positive control and found the rural and farming associations
      inconsistent by comparison. Graded REFUTE against the proxy being an
      established risk factor; it does not refute the compound-specific
      pesticide findings curated above, which rest on exposure-assessed studies
      rather than on residence.
  - reference: PMID:15177059
    reference_title: "Occupational and environmental risk factors for Parkinson's disease."
    supports: SUPPORT
    snippet: "While clear links to rural living, dietary factors, exposure to metals, head injury, and exposure to infectious diseases during childhood have not been established, there is general agreement that smoking and exposure to pesticides affect the probability of developing PD."
    explanation: This review notes that clear links to rural living are not established, indicating mixed evidence for this risk factor.
- name: Head Trauma
  influences_mechanisms:
  - target: Dopaminergic Neuron Loss
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Traumatic brain injury raises later risk of the disease by about half
      again. Pointed at the core neuropathological lesion rather than at a
      mechanism node because no cited sentence follows the injury to any
      particular step: neuroinflammation is the usual proposal and this entry
      holds a node for it, but nothing here measures that route, so the
      intermediates stay unknown. The evidence is also not consistent: a
      population-based meta-analysis found the association for dementia but not
      for this disease, so the link is curated with both results.
    evidence:
    - reference: PMID:36781627
      reference_title: "Traumatic brain injury and risk of Parkinson's disease: a meta-analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The risk ratio of TBI among PD and controls by a combination of 15 studies using a random-effect model was 1.48 (95% CI 1.22-1.74)."
      explanation: >-
        Meta-analysis of 15 studies giving a risk ratio of 1.48 for traumatic
        brain injury. It quantifies the exposure-disease association and not
        the neuronal loss this link targets.
    - reference: PMID:30396335
      reference_title: "Is traumatic brain injury a risk factor for neurodegeneration? A meta-analysis of population-based studies."
      supports: REFUTE
      evidence_source: HUMAN_CLINICAL
      snippet: "However, analyses of individual diagnoses found no evidence that the risk of Alzheimer's disease, and Parkinson's disease in individuals with previous TBI compared to those without TBI."
      explanation: >-
        Meta-analysis restricted to population-based studies, covering 3,263,207
        patients across 18 studies, which found injury associated with dementia
        overall but not with this disease specifically. Restricting to
        population-based designs removes the referral and recall bias that
        inflates hospital-based case-control estimates, so this null is the
        reason the link is PREDISPOSES rather than TRIGGERS.
  notes: >-
    No ECTO term binds this exposure. Searched the committed ECTO cache and the
    EBI Ontology Lookup Service for head, trauma, injury and concussion, and
    none of those queries returned an exposure class, so the entry is left
    unbound rather than forced onto an unrelated term. The two meta-analyses
    cited disagree, and the disagreement tracks study design rather than
    exposure definition.
  evidence:
  - reference: PMID:36781627
    reference_title: "Traumatic brain injury and risk of Parkinson's disease: a meta-analysis."
    supports: SUPPORT
    snippet: "The risk ratio of TBI among PD and controls by a combination of 15 studies using a random-effect model was 1.48 (95% CI 1.22-1.74)."
    explanation: This meta-analysis supports head trauma (TBI) as a risk factor for developing PD.
  - reference: PMID:30396335
    reference_title: "Is traumatic brain injury a risk factor for neurodegeneration? A meta-analysis of population-based studies."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "However, analyses of individual diagnoses found no evidence that the risk of Alzheimer's disease, and Parkinson's disease in individuals with previous TBI compared to those without TBI."
    explanation: >-
      The population-based null, curated beside the positive meta-analysis so
      the entry records a contested association rather than a settled one.
biochemical:
- name: Urine bis(monoacylglycerol)phosphate (BMP) isoforms
  context: >
    Urine BMP isoforms serve as accessible biomarkers for Parkinson's disease,
    with genetic variation in LRRK2 and GBA1 loci significantly modulating their
    levels. BMP is a lysosomal lipid that accumulates in cells with impaired
    autophagy-lysosomal pathway function, making it a proxy marker for
    lysosomal dysfunction in PD.
  notes: >-
    Sole support is a non-peer-reviewed preprint (PPR:PPR1273884, PPMI n=581).
    The BMP-LRRK2/GBA1 relationship is described there as a confirmation of a
    previously reported association; a peer-reviewed confirmatory citation is
    still outstanding.
  evidence:
  - reference: PPR:PPR1273884
    reference_title: "Genome-wide association studies identify genetic determinants of synucleinopathy biomarkers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conﬁrm strong associations between urine bis(monoacylglycerol)phosphate (BMP) isoforms and the variants LRRK2 p.G2019S and GBA1 p.N370S"
    explanation: PPMI GWAS confirms that urine BMP isoforms are modulated by LRRK2 and GBA1 variants and represent a genetically-influenced biomarker for PD, supporting lysosomal dysfunction as a measurable biological marker.
- name: Cerebrospinal fluid (CSF) amyloid-beta (Aβ)
  context: >
    CSF Aβ levels are modulated by APOE ε4 allele status and show complex
    associations with α-synucleinopathies. Lower CSF Aβ in PD may reflect
    concurrent amyloid pathology or altered CSF clearance, providing a
    quantitative readout of amyloid metabolism that is genetically influenced.
  notes: >-
    Sole support is a non-peer-reviewed preprint (PPR:PPR1273884, PPMI n=581).
    The cited snippet establishes an APOE genetic association only; the
    direction of CSF Ab change in PD is not asserted by this reference.
  evidence:
  - reference: PPR:PPR1273884
    reference_title: "Genome-wide association studies identify genetic determinants of synucleinopathy biomarkers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CSF Aβ was signiﬁcantly associated with an APOE ε4 allele, reinforcing its central role in amyloid regulation."
    explanation: PPMI GWAS shows that CSF Aβ levels are genetically modulated by APOE status, with the ε4 risk allele influencing amyloid metabolism in PD cohorts.
- name: Cerebrospinal fluid (CSF) ceramide isoforms
  context: >
    CSF ceramides are sphingolipids involved in lysosomal function and autophagy,
    with genetic variants at MCF2L2 and GMNN loci influencing their levels.
    Ceramide accumulation reflects impaired lysosomal lipid degradation and
    provides a direct readout of autophagy-lysosomal pathway dysfunction.
  notes: >-
    Reported as a NOVEL association by a single non-peer-reviewed preprint
    (PPR:PPR1273884, PPMI n=581) and not yet independently replicated. Treat the
    MCF2L2 and GMNN loci as provisional until confirmed.
  evidence:
  - reference: PPR:PPR1273884
    reference_title: "Genome-wide association studies identify genetic determinants of synucleinopathy biomarkers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Novel associations were detected between CSF ceramide isoforms the MCF2L2 and GMNN loci"
    explanation: PPMI GWAS identifies novel genetic associations between CSF ceramide isoforms and MCF2L2/GMNN loci, implicating these loci in lysosomal lipid metabolism dysregulation in PD.
- name: Cerebrospinal fluid (CSF) tau
  context: >
    CSF tau levels, including total tau and phosphorylated tau, show complex
    associations with PD and are influenced by genetic variation at the TP63
    locus. These tau biomarkers reflect both shared amyloid-tau pathology with
    Alzheimer's disease and PD-specific tau dysregulation.
  notes: >-
    Reported as a NOVEL association by a single non-peer-reviewed preprint
    (PPR:PPR1273884, PPMI n=581) and not yet independently replicated. Treat the
    TP63 locus as provisional until confirmed.
  evidence:
  - reference: PPR:PPR1273884
    reference_title: "Genome-wide association studies identify genetic determinants of synucleinopathy biomarkers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "between CSF tau and the TP63 locus"
    explanation: PPMI GWAS identifies a novel genetic association between CSF tau and the TP63 locus, suggesting TP63-mediated pathways influence tau metabolism or clearance in PD.
- name: Lysosomal lipid biomarkers
  context: >
    Multiple lysosomal lipid biomarkers (including ceramides, lactosylceramides,
    and sphingomyelins) are collectively associated with multiple PD risk loci
    (MAPT, SIPA1L2, MCCC1, RAB29). This locus-level convergence on a single
    lipid class is read as pathway-level evidence implicating autophagy-lysosomal
    clearance, rather than as a measured direction of change in PD.
  notes: >-
    Pathway-level roll-up over several lysosomal lipid analytes rather than a
    single measured biomarker; it overlaps the CSF ceramide entry above. Sole
    support is a non-peer-reviewed preprint (PPR:PPR1273884, PPMI n=581), which
    reports locus associations and does not establish the direction of change of
    these lipids in PD.
  evidence:
  - reference: PPR:PPR1273884
    reference_title: "Genome-wide association studies identify genetic determinants of synucleinopathy biomarkers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Multiple PD risk loci, including MAPT, SIPA1L2, MCCC1, and RAB29, were associated with lysosomal lipid biomarkers"
    explanation: PPMI GWAS shows that multiple established PD risk loci converge on lysosomal lipid biomarker dysregulation, suggesting that impaired lysosomal function is a shared mechanism across genetically heterogeneous PD and providing biomarker evidence for pathway-level convergence.
prevalence:
- population: Population aged 65 years and older (worldwide)
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 2500.0
  rate_low: 2000.0
  rate_high: 3000.0
  notes: >-
    Parkinson disease affects 2-3% of the population aged 65 years and older,
    making it the second-most common neurodegenerative disorder. Prevalence
    rises steeply with age.
  evidence:
  - reference: PMID:28332488
    reference_title: "Parkinson disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Parkinson disease is the second-most common neurodegenerative disorder that affects 2-3% of the population ≥65 years of age."
    explanation: >-
      This Nature Reviews Disease Primers review states that PD affects 2-3% of
      people aged 65 and older, supporting the point-prevalence estimate.
diagnosis:
- name: Motor Severity Rating (UPDRS)
  description: >-
    The Unified Parkinson's Disease Rating Scale (UPDRS), and its
    Movement-Disorder-Society-sponsored revision (MDS-UPDRS), are the
    clinician-administered instruments for rating motor and non-motor
    severity in PD. Hoehn and Yahr staging is modeled separately in the
    stages: section above, using the original five-stage scale.
  diagnosis_term:
    preferred_term: clinical assessment
    term:
      id: NCIT:C124351
      label: Clinical Evaluation
  measurements:
  - preferred_term: UPDRS
    term:
      id: LOINC:77717-7
      label: Unified Parkinson's Disease Rating Scale (UPDRS) panel
  notes: >-
    No reference_ranges band is recorded: UPDRS's individual item codes
    (Posture, Speech, Gait - parkinsons, Rigidity Neck, Depression scale,
    etc.) all resolve in LOINC but are never reproduced here. A LOINC code
    for the original (unmodified) Hoehn and Yahr stage was searched for and
    not found. Monarch KG queries run against api-v3.monarchinitiative.org/v3/api/search:
    "Hoehn" returns total: 0, "Hoehn and Yahr" returns total: 0, and
    "parkinson stage" returns total: 0; "Hoen" returns total: 1,
    LOINC:77714-4 Modified Hoen and Yahr stage [UPDRS]. That code asserts
    the modified 0.5-increment Hoehn and Yahr scale, which this entry does
    not use: the stages: section above carries the original five-stage
    scale, and PMID:15372591 (the MDS Task Force report, already cited
    there) recommends that, absent clinimetric validation of the modified
    version, "the original five-point scales should be maintained."
    LOINC:77714-4 is therefore left unbound rather than bound against
    evidence this entry does not support.
  evidence:
  - reference: PMID:19025984
    reference_title: "Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS): scale presentation and clinimetric testing results."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Movement disorder specialists and study coordinators administered the UPDRS (55 items) and MDS-UPDRS (65 items) to 877 English speaking (78% non-Latino Caucasian) patients with Parkinson's disease from 39 sites."
    explanation: Establishes UPDRS and its MDS-sponsored revision as the clinician-administered instruments used at scale to assess PD severity, rather than citing an incidental outcome measure from a single rehabilitation case report.
  - reference: PMID:19025984
    reference_title: "Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS): scale presentation and clinimetric testing results."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The combined clinimetric results of this study support the validity of the MDS-UPDRS for rating PD."
    explanation: Supports the clinimetric validity of the MDS-UPDRS revision, which correlated highly with the original UPDRS (rho = 0.96) bound here.
treatments:
- name: Levodopa/Carbidopa
  description: Gold standard treatment, replaces dopamine precursor.
  evidence:
  - reference: PMID:27577098
    reference_title: "Current and experimental treatments of Parkinson disease: A guide for neuroscientists."
    supports: SUPPORT
    snippet: "The symptomatic treatment of the motor symptoms of Parkinson disease (PD) has been constantly optimized using pharmacotherapy (L-Dopa, several dopamine agonists, inhibitors of monoamine oxidase (MAO)-B and catechol-o-methyltransferase (COMT), and amantadine), deep brain stimulation, and physiotherapy."
    explanation: This review identifies L-Dopa as a core pharmacotherapy for PD motor symptoms.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: levodopa
      term:
        id: CHEBI:15765
        label: L-dopa
    - preferred_term: carbidopa
      term:
        id: CHEBI:3395
        label: carbidopa
  target_mechanisms:
  - target: Striatal Dopamine Deficiency
    treatment_effect: RESTORES
    description: Levodopa supplies dopamine precursor to partially restore dopaminergic signaling in dopamine-depleted striatal circuits.
- name: Dopamine Agonists
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Directly stimulate dopamine receptors. Carries a class-level risk of impulse control
    behaviors: dopamine agonist exposure raises the odds of an ICD roughly 2- to 3.5-fold,
    and the association holds across pramipexole and ropinirole rather than being specific
    to one agent. See the Impulse Control Behaviors phenotype.
  evidence:
  - reference: PMID:27577098
    reference_title: "Current and experimental treatments of Parkinson disease: A guide for neuroscientists."
    supports: SUPPORT
    snippet: "The symptomatic treatment of the motor symptoms of Parkinson disease (PD) has been constantly optimized using pharmacotherapy (L-Dopa, several dopamine agonists, inhibitors of monoamine oxidase (MAO)-B and catechol-o-methyltransferase (COMT), and amantadine), deep brain stimulation, and physiotherapy."
    explanation: This review identifies dopamine agonists as part of standard pharmacotherapy for PD.
  - reference: PMID:20457959
    reference_title: "Impulse control disorders in Parkinson disease: a cross-sectional study of 3090 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dopamine agonist treatment in PD is associated with 2- to 3.5-fold increased odds of having an ICD. This association represents a drug class relationship across ICDs."
    explanation: >-
      Establishes the impulse-control adverse effect as a property of the dopamine agonist
      drug class rather than of an individual agent, which is why it is recorded on this
      treatment entry and not only on the phenotype.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_mechanisms:
  - target: Striatal Dopamine Deficiency
    treatment_effect: BYPASSES
    description: Dopamine agonists bypass reduced endogenous dopamine by directly stimulating dopamine receptors in downstream circuits.
  - target: Postsynaptic D2/D3 Receptor Occupancy by Agonist Therapy
    treatment_effect: ACTIVATES
    description: The agonist occupies and activates the postsynaptic receptor directly; the existing BYPASSES edge records the consequence of doing so while presynaptic dopamine is deficient.
- name: Impulse Control Behavior Management
  description: >-
    Management of dopaminergic-therapy-related impulse control behaviors. The first-line step
    in practice is reduction or withdrawal of the dopamine agonist; the interventions studied
    beyond that are cognitive behavioural therapy, levodopa infusion, atomoxetine, naltrexone,
    valproic acid, and deep brain stimulation. The evidence base is small and preliminary - a
    narrative synthesis of 10 studies totalling 283 patients - so this is recorded as a
    treatable target rather than as established therapy.
  evidence:
  - reference: PPR:PPR1298507
    reference_title: "Prevalence and Treatment of Impulse Control Behaviours in Parkinson's Disease: A Meta-Analysis and Systematic Review"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A narrative synthesis of 10 studies (n = 283) found preliminary evidence for the effectiveness of cognitive behavioural therapy, levodopa infusion, atomoxetine, naltrexone, valproic acid, and deep brain stimulation in supporting ICB reduction."
    explanation: >-
      The source for the intervention list and for the strength of the claim - preliminary
      evidence from a narrative synthesis, not pooled effect estimates.
  treatment_term:
    preferred_term: Therapeutic Procedure
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
  target_mechanisms:
  - target: Impulse Control Behaviors
    treatment_effect: INHIBITS
    description: >-
      These interventions are studied as ways to reduce impulse control behaviors themselves,
      which is what connects this phenotype to the treatment graph.
- name: MAO-B Inhibitors
  description: Prevent dopamine breakdown (selegiline, rasagiline).
  evidence:
  - reference: PMID:27577098
    reference_title: "Current and experimental treatments of Parkinson disease: A guide for neuroscientists."
    supports: SUPPORT
    snippet: "The symptomatic treatment of the motor symptoms of Parkinson disease (PD) has been constantly optimized using pharmacotherapy (L-Dopa, several dopamine agonists, inhibitors of monoamine oxidase (MAO)-B and catechol-o-methyltransferase (COMT), and amantadine), deep brain stimulation, and physiotherapy."
    explanation: This review lists MAO-B inhibitors among standard PD pharmacotherapies.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: selegiline
      term:
        id: CHEBI:50217
        label: selegiline
    - preferred_term: rasagiline
      term:
        id: CHEBI:63620
        label: rasagiline
  target_mechanisms:
  - target: Striatal Dopamine Deficiency
    treatment_effect: MODULATES
    description: MAO-B inhibitors prolong dopamine signaling by reducing dopamine breakdown.
- name: COMT Inhibitors
  description: Extend levodopa duration (entacapone).
  evidence:
  - reference: PMID:27577098
    reference_title: "Current and experimental treatments of Parkinson disease: A guide for neuroscientists."
    supports: SUPPORT
    snippet: "The symptomatic treatment of the motor symptoms of Parkinson disease (PD) has been constantly optimized using pharmacotherapy (L-Dopa, several dopamine agonists, inhibitors of monoamine oxidase (MAO)-B and catechol-o-methyltransferase (COMT), and amantadine), deep brain stimulation, and physiotherapy."
    explanation: This review lists COMT inhibitors among standard PD pharmacotherapies.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: entacapone
      term:
        id: CHEBI:4798
        label: entacapone
  target_mechanisms:
  - target: Striatal Dopamine Deficiency
    treatment_effect: MODULATES
    description: COMT inhibitors extend levodopa-derived dopaminergic signaling and indirectly modulate striatal dopamine deficiency.
- name: Deep Brain Stimulation
  description: Surgical therapy for advanced motor fluctuations.
  evidence:
  - reference: PMID:27577098
    reference_title: "Current and experimental treatments of Parkinson disease: A guide for neuroscientists."
    supports: SUPPORT
    snippet: "The symptomatic treatment of the motor symptoms of Parkinson disease (PD) has been constantly optimized using pharmacotherapy (L-Dopa, several dopamine agonists, inhibitors of monoamine oxidase (MAO)-B and catechol-o-methyltransferase (COMT), and amantadine), deep brain stimulation, and physiotherapy."
    explanation: This review identifies deep brain stimulation as a standard symptomatic therapy for PD.
  treatment_term:
    preferred_term: deep brain stimulation
    term:
      id: NCIT:C21024
      label: Deep Brain Stimulation
  target_mechanisms:
  - target: Basal Ganglia Circuit Dysfunction
    treatment_effect: MODULATES
    description: DBS modulates abnormal basal ganglia motor circuit activity rather than acting upstream on dopaminergic neuron loss.
- name: Physical Therapy
  description: Maintains mobility and reduces fall risk. Exercise programs including PWR!Moves, Rock Steady Boxing, Dance for Parkinson's, yoga, and tai chi are evidence-based approaches that specifically reduce rigidity, improve postural stability, and enhance motor fluidity through rebalancing of basal ganglia circuits.
  evidence:
  - reference: PMID:27577098
    reference_title: "Current and experimental treatments of Parkinson disease: A guide for neuroscientists."
    supports: SUPPORT
    snippet: "The symptomatic treatment of the motor symptoms of Parkinson disease (PD) has been constantly optimized using pharmacotherapy (L-Dopa, several dopamine agonists, inhibitors of monoamine oxidase (MAO)-B and catechol-o-methyltransferase (COMT), and amantadine), deep brain stimulation, and physiotherapy."
    explanation: This review lists physiotherapy as part of symptomatic treatment for PD.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Stretching and range-of-motion exercises (e.g., PWR!Moves), strengthening exercises (e.g., Rock Steady Boxing), dancing (e.g., Dance for Parkinson's Disease), and yoga and tai chi help reduce stiffness"
    explanation: Comprehensive review identifies multiple evidence-based exercise modalities that effectively reduce rigidity and motor stiffness in PD.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tai Chi was found to be effective, alongside resistance and stretching, for improving motor symptoms, physical abilities, and quality of life in early to mid-stage PD"
    explanation: Tai Chi demonstrates measurable benefit for multiple motor domains including endurance, control, and postural stability in PD.
  - reference: PMID:42646502
    reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A study measured motor and non-motor symptom changes in PD participants after the 8-week ‘PWR!Moves’ program, a multidisciplinary wellness course"
    quote_role: REVIEW_SYNTHESIS
    explanation: >-
      Supports structured exercise as a management component. The snippet was
      moved to the sentence that names the study and its 8-week PWR!Moves
      intervention, so it is self-describing; the adjacent result sentence
      ("Most improved in three of four UPDRS areas") could not be quoted
      together with it, because the citation marker between the two is stripped
      before substring matching. Graded REVIEW_SYNTHESIS: this review is
      reporting study [352] rather than presenting its own result.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_mechanisms:
  - target: Basal Ganglia Circuit Dysfunction
    treatment_effect: MODULATES
    description: >-
      Structured exercise is reported to shift the excitatory/inhibitory balance
      within the basal ganglia rather than route around it. Cueing and
      compensation strategies, which do work around the circuit, are delivered
      alongside it; MODULATES records the claim this entry actually cites
      evidence for.
    evidence:
    - reference: PMID:42646502
      reference_title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: "Exercise helps reestablish the balance between excitatory and inhibitory signals in the basal ganglia, decreasing excitotoxicity and enhancing movement"
      explanation: >-
        Link-level evidence for the mechanism of action asserted by this edge.
        Graded OTHER with quote_role REVIEW_SYNTHESIS: the sentence is the
        review's synthesis of its references [305-308] under the heading
        "Modulation of glutamate and motor circuits", not a result this
        publication reports.
- name: Botulinum Neurotoxin A (BoNT/A) for Depression
  description: >
    Botulinum toxin type A alleviates depression in Parkinson's disease by inhibiting
    the complement C3-C3aR signaling axis and reducing microglial synaptic phagocytosis.
    This represents a novel complement-targeted approach to managing depression as a
    non-motor symptom in PD, distinct from BoNT/A's canonical motor symptom applications.
  evidence:
  - reference: PMID:42263400
    reference_title: "The complement C3-microglial axis in depression of Parkinson's disease: from mechanism to therapeutic intervention."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "BoNT/A treatment alleviated depressive-like behaviours and reduced microglial synaptic engulfment in an MPTP model; these therapeutic effects were abolished in C3-/- and C3aR-/- mice."
    explanation: >
      Mouse PD model demonstrates that BoNT/A alleviates depression-like behavior through
      inhibition of the C3-C3aR complement axis, preventing microglial synaptic engulfment
      and protecting against synapse loss in the hippocampus.
  treatment_term:
    preferred_term: botulinum toxin type A therapy
    term:
      id: NCIT:C157775
      label: Botulinum Toxin Therapy
  target_mechanisms:
  - target: Complement C3-C3aR Activation in Depression
    treatment_effect: INHIBITS
    description: >
      BoNT/A suppresses complement C3-C3aR signaling through modulation of microglial
      phagocytosis-related functions, reducing microglial activation and synaptic
      phagocytosis, thereby alleviating depression-like symptoms in PD models.
datasets:
# Parkinson's Disease Gut Microbiome Studies
- accession: bioproject:PRJNA834801
  title: Large-scale metagenomics of Parkinson's disease gut microbiome
  description: >-
    Shotgun metagenomics from the NeuroGenetics Research Consortium (NGRC)
    with over 30% of species, genes and pathways showing altered abundances
    in PD. Identified polymicrobial clusters and competitive relationships.
  organism:
    preferred_term: human gut metagenome
    term:
      id: NCBITaxon:408170
      label: human gut metagenome
  data_type: WGS
  sample_types:
  - preferred_term: fecal sample
    term:
      id: OBI:0002503
      label: feces specimen
    tissue_term:
      preferred_term: feces
      term:
        id: UBERON:0001988
        label: feces
  conditions:
  - Parkinson's disease
  - healthy controls
  publication: PMID:36357667
  notes: Nature Communications 2022 - largest PD metagenomics to date
  evidence:
  - reference: PMID:37449597
    reference_title: "Gut-microbiome-brain axis: the crosstalk between the vagus nerve, alpha-synuclein and the brain in Parkinson's disease."
    supports: SUPPORT
    snippet: "This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."
    explanation: This supports the relevance of gut microbiome datasets to PD mechanisms.

- accession: bioproject:PRJNA782492
  title: Multi-omics analysis of PD gut microbiome gene expression
  description: >-
    Integrated metagenomics and metatranscriptomics analyzing microbiome gene
    co-expression networks in Parkinson's disease. Observed significant
    depletion of hub genes in PD patients.
  organism:
    preferred_term: human gut metagenome
    term:
      id: NCBITaxon:408170
      label: human gut metagenome
  data_type: WGS
  sample_types:
  - preferred_term: fecal sample
    term:
      id: OBI:0002503
      label: feces specimen
    tissue_term:
      preferred_term: feces
      term:
        id: UBERON:0001988
        label: feces
  conditions:
  - Parkinson's disease
  - healthy controls
  notes: npj Biofilms and Microbiomes 2025 - multi-omics approach
  evidence:
  - reference: PMID:37449597
    reference_title: "Gut-microbiome-brain axis: the crosstalk between the vagus nerve, alpha-synuclein and the brain in Parkinson's disease."
    supports: SUPPORT
    snippet: "This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."
    explanation: This supports the relevance of gut microbiome datasets to PD mechanisms.

- accession: bioproject:PRJNA808166
  title: Longitudinal gut microbiome in Parkinson's disease
  description: >-
    Longitudinal study investigating gut microbiome changes in PD patients
    and impact of device-assisted therapies. Tracks microbiome alterations
    with disease progression.
  organism:
    preferred_term: human gut metagenome
    term:
      id: NCBITaxon:408170
      label: human gut metagenome
  sample_types:
  - preferred_term: fecal sample
    term:
      id: OBI:0002503
      label: feces specimen
    tissue_term:
      preferred_term: feces
      term:
        id: UBERON:0001988
        label: feces
  conditions:
  - Parkinson's disease baseline
  - Parkinson's disease follow-up
  notes: Frontiers Aging Neuroscience 2022 - longitudinal design
  evidence:
  - reference: PMID:37449597
    reference_title: "Gut-microbiome-brain axis: the crosstalk between the vagus nerve, alpha-synuclein and the brain in Parkinson's disease."
    supports: SUPPORT
    snippet: "This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."
    explanation: This supports the relevance of gut microbiome datasets to PD mechanisms.

- accession: bioproject:PRJNA530401
  title: PD gut microbiome meta-analysis cohort
  description: >-
    Metagenomic sequencing data from PD patients and controls contributing
    to cross-cohort meta-analyses. Identified alterations linked to
    intestinal inflammation including reduced butyrate producers.
  organism:
    preferred_term: human gut metagenome
    term:
      id: NCBITaxon:408170
      label: human gut metagenome
  data_type: WGS
  sample_types:
  - preferred_term: fecal sample
    term:
      id: OBI:0002503
      label: feces specimen
    tissue_term:
      preferred_term: feces
      term:
        id: UBERON:0001988
        label: feces
  conditions:
  - Parkinson's disease
  - healthy controls
  notes: npj Parkinson's Disease 2021 - meta-analysis contributing cohort
  evidence:
  - reference: PMID:37449597
    reference_title: "Gut-microbiome-brain axis: the crosstalk between the vagus nerve, alpha-synuclein and the brain in Parkinson's disease."
    supports: SUPPORT
    snippet: "This critical review of the literature shows that there is a close link between the microbiome, the gut, and the brain in Parkinson's disease."
    explanation: This supports the relevance of gut microbiome datasets to PD mechanisms.

- accession: metabolights:MTBLS2266
  title: Metabolomics of sebum reveals lipid dysregulation in Parkinson's disease
  description: >-
    LC-MS sebum metabolomics in Parkinson's disease, including drug-naive and
    medicated cohorts, compared with well-matched controls to identify lipid
    pathway alterations.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: METABOLOMICS
  sample_count: 274
  conditions:
  - Parkinson's disease
  - drug-naive Parkinson's disease
  - medicated Parkinson's disease
  - healthy controls
  publication: PMID:33707447
  findings:
  - statement: Sebum metabolomics in PD shows alterations in lipid metabolism pathways, including the carnitine shuttle, sphingolipid metabolism, arachidonic acid metabolism and fatty acid biosynthesis.
    evidence:
    - reference: metabolights:MTBLS2266
      reference_title: "Metabolomics of sebum reveals lipid dysregulation in Parkinson's disease"
      supports: SUPPORT
      snippet: "Pathway enrichment analysis shows alterations in lipid metabolism related to the carnitine shuttle, sphingolipid metabolism, arachidonic acid metabolism and fatty acid biosynthesis."
      explanation: The dataset description reports lipid pathway alterations detected in sebum metabolomics for PD.
  - statement: LC-MS profiling of 274 participants detected metabolites predictive of PD phenotype.
    evidence:
    - reference: metabolights:MTBLS2266
      reference_title: "Metabolomics of sebum reveals lipid dysregulation in Parkinson's disease"
      supports: SUPPORT
      snippet: "We used liquid chromatography-mass spectrometry (LC-MS) to analyse 274 samples from participants (80 drug naïve PD, 138 medicated PD and 56 well matched control subjects) and detected metabolites that could predict PD phenotype."
      explanation: The dataset description specifies LC-MS profiling and the PD/control cohort sizes.
  evidence:
  - reference: metabolights:MTBLS2266
    reference_title: "Metabolomics of sebum reveals lipid dysregulation in Parkinson's disease"
    supports: SUPPORT
    snippet: "Here, we use a metabolomics profiling approach to identify changes to lipids in PD observed in sebum, a non-invasively available biofluid."
    explanation: Establishes that the dataset focuses on PD sebum metabolomics.
  notes: Metabolomics profiling of sebum as a non-invasive biofluid for PD.

- accession: metabolights:MTBLS10743
  title: Metabolomic Changes in Idiopathic and GBA1 Parkinson’s Disease
  description: >-
    Mass spectrometry metabolomics comparing idiopathic Parkinson's disease and
    GBA1-associated Parkinson's disease cohorts with controls.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: METABOLOMICS
  conditions:
  - idiopathic Parkinson's disease
  - GBA1-associated Parkinson's disease
  - healthy controls
  findings:
  - statement: Metabolomic signatures differ between GBA1-PD and idiopathic PD in sebum and serum with good specificity and sensitivity.
    evidence:
    - reference: metabolights:MTBLS10743
      reference_title: "Metabolomic Changes in Idiopathic and GBA1 Parkinson's Disease"
      supports: SUPPORT
      snippet: "Differences in metabolomic signatures were seen between ... GBA1-PD and iPD in sebum and serum with good specificity and sensitivity."
      explanation: The dataset description reports discriminative metabolomic signatures between GBA1-PD and idiopathic PD.
  - statement: Serum pathways implicated include sphingolipid metabolism, amino sugar metabolism and amino acid pathways, while sebum features are hypothesised to be lipid degradation products.
    evidence:
    - reference: metabolights:MTBLS10743
      reference_title: "Metabolomic Changes in Idiopathic and GBA1 Parkinson's Disease"
      supports: SUPPORT
      snippet: "Significant pathways in serum included sphingolipid metabolism, amino sugar metabolism and amino acid pathways, whereas significant features between groups in sebum are hypothesised to be lipid degradation products."
      explanation: The dataset description lists pathway-level differences in serum and hypothesized lipid degradation products in sebum.
  evidence:
  - reference: metabolights:MTBLS10743
    reference_title: "Metabolomic Changes in Idiopathic and GBA1 Parkinson's Disease"
    supports: SUPPORT
    snippet: "Here, we use mass spectrometry based metabolomics to analyse serum and sebum samples from 50 genotyped participants and find differences in lipid and sugar regulation, oxidative stress and the production of amino acids and neurotransmitters which distinguish ... GBA1-PD from iPD."
    explanation: Establishes the dataset's serum and sebum metabolomics design distinguishing GBA1-PD from idiopathic PD.
  notes: Preprint dataset describing metabolic changes in idiopathic vs GBA1 PD.

# CELLxGENE - Multi-region single nucleus PD atlas
- accession: "cellxgene:d5d0df8f-4eee-49d8-a221-a288f50a1590"
  title: A multi-region single nucleus transcriptomic atlas of Parkinson's disease
  description: >-
    Single-nucleus RNA-seq atlas of Parkinson's disease spanning multiple brain
    regions, providing cell-type-resolved transcriptomic profiles of dopaminergic
    neurons and glial populations in PD and healthy controls.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: SINGLE_CELL_RNA_SEQ
  sample_types:
  - preferred_term: brain tissue
    tissue_term:
      preferred_term: brain
      term:
        id: UBERON:0000955
        label: brain
  conditions:
  - Parkinson's disease
  - healthy controls
  publication: PMID:39317733
  notes: CZI CELLxGENE collection. DOI 10.1038/s41597-024-04117-y. Multi-region snRNA-seq atlas enabling virtual cell model training on PD-relevant cell states.

experimental_models:
- name: Midbrain organoids with dopaminergic differentiation
  experimental_model_type: ORGANOID
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_source: Human pluripotent stem cells differentiated toward midbrain fate
  culture_system: 3D self-organizing midbrain organoid cultures
  publication: PMID:42727800
  description: >-
    Three-dimensional midbrain organoids reproduce aspects of human midbrain development. The review concludes
    they reliably reproduce mitochondrial and lysosomal dysfunction and, in SNCA triplication models, alpha-synuclein
    accumulation, but seldom progressive dopaminergic neurodegeneration or mature Lewy pathology.
  modeled_mechanisms:
  - target: Mitochondrial Dysfunction
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Organoids reproduce mitochondrial dysfunction as reported in the reviewed organoid studies.
    limitations: >-
      Reported across organoid studies generally; the review does not tie this to a single genotype or cell population.
    evidence:
    - reference: PMID:42727800
      reference_title: "Midbrain organoids as next-generation models for Parkinson's disease: From pathogenesis to therapeutic discovery."
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: REVIEW_SYNTHESIS
      snippet: "Organoids reliably reproduce mitochondrial and lysosomal dysfunction"
      explanation: >-
        The review synthesizes organoid studies as reproducing mitochondrial dysfunction, which supports treating
        midbrain organoids as informative for this node.
  - target: Autophagy-Lysosome Pathway Dysfunction
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Organoids reproduce lysosomal dysfunction as reported in the reviewed organoid studies.
    limitations: >-
      Reported across organoid studies generally; the review does not tie this to a single genotype or cell population.
    evidence:
    - reference: PMID:42727800
      reference_title: "Midbrain organoids as next-generation models for Parkinson's disease: From pathogenesis to therapeutic discovery."
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: REVIEW_SYNTHESIS
      snippet: "Organoids reliably reproduce mitochondrial and lysosomal dysfunction"
      explanation: >-
        The review synthesizes organoid studies as reproducing lysosomal dysfunction, which supports treating midbrain
        organoids as informative for this node.
  - target: Alpha-Synuclein Aggregation
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Alpha-synuclein accumulation is reproduced in SNCA triplication organoid models.
    limitations: >-
      Accumulation is shown only in SNCA triplication models; the review reports that organoids rarely mature into Lewy pathology.
    divergences:
    - divergence_type: BOUNDARY_OMISSION
      materiality: QUALIFYING
      description: >-
        Organoid cultures last weeks to months and lack the decades of neuronal aging over which
        alpha-synuclein matures into Lewy bodies in patients, so the model captures early accumulation
        but rarely the mature inclusion stage of this node.
    evidence:
    - reference: PMID:42727800
      reference_title: "Midbrain organoids as next-generation models for Parkinson's disease: From pathogenesis to therapeutic discovery."
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: REVIEW_SYNTHESIS
      snippet: "in SNCA triplication models, α-synuclein accumulation"
      explanation: >-
        The review reports alpha-synuclein accumulation in SNCA triplication organoid models, supporting the
        aggregation node only for that genetic setting.
  - target: Dopaminergic Neuron Loss
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: CELLULAR
    description: >-
      Organoids contain dopaminergic neurons, but the progressive, age-dependent course of their loss in patients
      is rarely reproduced.
    limitations: >-
      The review states organoids seldom show progressive neurodegeneration, so the progressive course of this
      node is rarely reproduced in the reported studies. The review does not state that dopaminergic neuron loss
      is absent from organoids.
    divergences:
    - divergence_type: BOUNDARY_OMISSION
      materiality: QUALIFYING
      description: >-
        The slow, decades-long progression of nigral dopaminergic neuron loss in patients falls outside an organoid
        culture's lifespan, so the model can show dopaminergic vulnerability but rarely the progressive degeneration
        this node describes.
    evidence:
    - reference: PMID:42727800
      reference_title: "Midbrain organoids as next-generation models for Parkinson's disease: From pathogenesis to therapeutic discovery."
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: REVIEW_SYNTHESIS
      snippet: "but seldom progressive neurodegeneration or mature Lewy pathology"
      explanation: >-
        The review reports that organoids seldom reproduce progressive neurodegeneration, which supports treating
        them as only partially informative for this node: the progressive course of the loss is rarely captured.

animal_models:
- name: Drosophila Dap160 heterozygous null with human alpha-synuclein expression
  species: Drosophila melanogaster
  genotype: >-
    Heterozygous amorphic Dap160 (ITSN1 ortholog) allele with pan-neuronal
    (elav-GAL4) or eye-specific (GMR-GAL4) expression of human wild-type
    alpha-synuclein (UAS-SNCA)
  publication: PMID:40056900
  description: >-
    A genetic-interaction model for ITSN1 haploinsufficiency. Halving the fly
    ortholog Dap160 worsens alpha-synuclein-induced photoreceptor degeneration
    and age-dependent motor decline, while Dap160 overexpression lessens the eye
    degeneration. Dap160 heterozygotes without alpha-synuclein have no eye or
    motor phenotype.
  modeled_mechanisms:
  - target: Dopaminergic Neuron Loss
    relationship: PERTURBS
    fidelity: LOW
    model_scale: ORGANISM
    description: >-
      Reduced Dap160 dosage enhances the neurodegeneration and motor decline
      caused by overexpressed human alpha-synuclein.
    limitations: >-
      Alpha-synuclein is overexpressed from a transgene rather than present at
      endogenous levels, the degeneration readout is in photoreceptors rather
      than dopaminergic neurons, and the motor assay uses pan-neuronal
      expression, so neither readout measures dopaminergic neuron loss
      directly.
    readouts:
    - name: Alpha-synuclein-induced rough-eye degeneration
      target: Dopaminergic Neuron Loss
      direction: INCREASED
      interpretation: >-
        Larger disorganized eye area in Dap160 heterozygotes expressing
        alpha-synuclein than in alpha-synuclein flies alone.
      evidence:
      - reference: PMID:40056900
        reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Flies carrying a heterozygous null variant in Dap160 (the Drosophila
          ortholog of ITSN1)31 had exacerbated α-synuclein-induced degeneration,
          with more severe disorganization covering a larger eye area
        explanation: Reports the eye-degeneration measurement and its direction.
    - name: Climbing speed in alpha-synuclein-expressing flies
      target: Dopaminergic Neuron Loss
      direction: DECREASED
      interpretation: >-
        Dap160 heterozygosity worsens the age-dependent loss of climbing speed
        and increase in stumbling caused by neuronal alpha-synuclein.
      evidence:
      - reference: PMID:40056900
        reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Heterozygous loss of Dap160 worsened the phenotypes of
          α-synuclein-expressing flies across all ages
        explanation: Reports the locomotor readout across ages.
  - target: Alpha-Synuclein Aggregation
    relationship: MEASURES
    fidelity: LOW
    model_scale: CELLULAR
    description: >-
      Dap160 colocalizes with alpha-synuclein aggregates at synaptic boutons.
    limitations: >-
      Aggregate burden itself was not quantified across Dap160 genotypes, so
      the model places the ITSN1 ortholog at aggregates but does not show that
      ITSN1 dosage changes aggregation.
    evidence:
    - reference: PMID:40056900
      reference_title: "Haploinsufficiency of ITSN1 is associated with a substantial increased risk of Parkinson's disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Dap160 co-localized with α-synuclein aggregates in 42.9% of 245 analyzed
        synaptic boutons
      explanation: >-
        Places the ITSN1 ortholog at alpha-synuclein aggregates in fly
        synapses, supporting the link to this node.
discussions:
- discussion_id: pd_pgc1a_therapeutic_window
  prompt: >-
    Does restoring PGC-1alpha signaling protect nigral dopaminergic neurons in
    human Parkinson disease, given that rescue is seen in cellular models while
    sustained supraphysiological expression in the adult rat nigrostriatal
    system is itself dopaminergic-toxic?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#PGC-1alpha Transcriptional Program Repression
  - pathophysiology#Mitochondrial Dysfunction
  rationale: >-
    The direction of the human observation is not in doubt: PGC-1alpha-responsive
    bioenergetic genes are underexpressed in laser-captured human nigral neurons
    early in disease, and the repressor PARIS accumulates in human Parkinson
    disease brain. What does not transfer cleanly from model to patient is the
    therapeutic inverse. Cellular models show that activating PGC-1alpha blocks
    alpha-synuclein- and rotenone-induced dopaminergic loss, but AAV-mediated
    sustained overexpression in the adult rat nigrostriatal system selectively
    impairs dopaminergic function and, at higher levels, causes overt
    degeneration - and it does not rescue alpha-synuclein-induced degeneration.
    PGC-1alpha therefore behaves as a rheostat with an activation-level, cell-type,
    isoform and disease-stage dependence rather than as a monotonic neuroprotective
    switch, so a positive result in one model system cannot be read as evidence
    that pathway activation is protective in patients. Recording this as a
    HUMAN_MODEL_MISMATCH rather than a plain KNOWLEDGE_GAP is deliberate: the
    model evidence exists and is abundant on both sides; it is its translational
    validity, and specifically the existence and width of a therapeutic window,
    that is unresolved. This gap is shared with other neurodegenerative entries
    (Huntington disease, Alzheimer disease, amyotrophic lateral sclerosis) in
    which the same coactivator is implicated.
  proposed_experiments:
  - experiment_id: exp_pd_pgc1a_dose_response_nigrostriatal
    name: Dose-graded PGC-1alpha activation in nigrostriatal models
    description: >-
      Titrate PGC-1alpha activity across a graded range - from partial
      restoration toward physiological levels up to the supraphysiological
      levels used in the AAV overexpression studies - in human iPSC-derived
      midbrain dopaminergic neurons and in an in vivo nigrostriatal model,
      reading out respiratory-chain subunit expression, mitochondrial membrane
      potential, dopamine content and dopaminergic survival at each level.
    experiment_type:
      preferred_term: dose-response perturbation study
    decision_criterion: >-
      A therapeutic window exists if there is a contiguous range of PGC-1alpha
      activity in which bioenergetic readouts improve without loss of
      dopaminergic markers or dopamine content; the rheostat model predicts an
      inverted-U with toxicity at the high end, whereas a simple neuroprotective
      model predicts monotonic benefit.
  - experiment_id: exp_pd_pgc1a_target_engagement_biomarker
    name: Human target-engagement biomarker for PGC-1alpha modulation
    description: >-
      Establish and validate a measurable readout of PGC-1alpha pathway
      engagement in living patients - for example a peripheral or CSF
      transcriptional signature of the PGC-1alpha-responsive gene set benchmarked
      against the postmortem nigral signature - so that a trial of any
      PGC-1alpha-directed agent can distinguish target-engagement failure from
      mechanism failure.
    experiment_type:
      preferred_term: biomarker validation study
    decision_criterion: >-
      The biomarker is usable if it shifts dose-dependently with a known
      PGC-1alpha modulator and correlates with the nigral PGC-1alpha-responsive
      gene-set deficit; absent such a readout, a negative clinical trial cannot
      be interpreted as refuting the mechanism.
  evidence:
  - reference: PMID:22246294
    reference_title: "Sustained expression of PGC-1α in the rat nigrostriatal system selectively impairs dopaminergic function."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In the adult rat nigrostriatal system, adeno-associated virus (AAV)-mediated overexpression of PGC-1α induces the selective loss of dopaminergic markers and increases dopamine (DA) catabolism, leading to a reduction in striatal DA content."
    explanation: >-
      The in vivo counterexample to the cellular rescue result: sustained
      pathway activation is itself dopaminergic-toxic, which is what creates the
      translational uncertainty.
  - reference: PMID:22246294
    reference_title: "Sustained expression of PGC-1α in the rat nigrostriatal system selectively impairs dopaminergic function."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These results highlight the central role of PGC-1α in the function and survival of dopaminergic neurons and the critical need for maintaining physiological levels of PGC-1α activity."
    explanation: >-
      States the therapeutic-window requirement directly - benefit is
      conditional on activity level, not on activation per se.
  - reference: PMID:42430091
    reference_title: "The Role of PGC-1α in Neurodegenerative Diseases: Molecular Mechanisms, Translational Challenges, and Therapeutic Potential."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "These observations suggest that PGC-1α is not a simple neuroprotective switch, but a flexible regulatory hub whose therapeutic value depends on cell type, isoform profile, disease stage, and activation level."
    explanation: >-
      Cross-disease review framing that generalizes the mismatch beyond
      Parkinson disease and names the four context variables that determine
      whether modulation helps.
  notes: >-
    Raised from dismech issue #6114 ([kgap-scan:scope] PGC-1alpha-mediated
    neuroprotection), which asked whether the Parkinson, Alzheimer and
    amyotrophic lateral sclerosis entries should carry a PGC-1alpha node. The
    Huntington disease entry already curates the mHTT-driven PGC-1alpha
    repression chain; Alzheimer disease and amyotrophic lateral sclerosis remain
    uncurated for this mechanism.
- discussion_id: gap_pd_microbiome_causal_direction_body_first
  prompt: >-
    In body-first Parkinson disease, are gut microbiome dysbiosis and
    intestinal barrier/inflammatory changes causal triggers for enteric
    alpha-synuclein seeding, modifiers that amplify an already initiated
    synucleinopathy, or secondary consequences of autonomic gut dysfunction?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Gut Microbiome Dysbiosis
  - pathophysiology#Intestinal Inflammation and Barrier Dysfunction
  - pathophysiology#Enteric Alpha-Synuclein Seeding
  - pathophysiology#Vagal-Brainstem Alpha-Synuclein Propagation
  rationale: >-
    Cross-sectional human studies support PD-associated dysbiosis and elevated
    intestinal inflammatory/permeability markers, while animal studies support
    gut-to-brain alpha-synuclein propagation through the vagus nerve. The
    unresolved step is temporal and causal: whether dysbiosis or barrier
    dysfunction initiates enteric alpha-synuclein misfolding in humans, merely
    accelerates propagation, or appears after autonomic denervation has already
    altered gut physiology.
  proposed_experiments:
  - experiment_id: exp_pd_prodromal_microbiome_barrier_alpha_syn_longitudinal_cohort
    name: Prodromal microbiome-barrier alpha-synuclein longitudinal cohort
    description: >-
      Follow iRBD-, constipation-, and hyposmia-enriched prodromal cohorts with
      serial stool metagenomics, SCFA/metabolite profiling, fecal and serum
      calprotectin/zonulin, autonomic imaging, and standardized enteric
      alpha-synuclein biopsy assays before motor conversion.
    experiment_type:
      preferred_term: longitudinal prodromal multi-omics cohort study
    readouts:
    - name: Microbiome dysbiosis trajectory
      target: pathophysiology#Gut Microbiome Dysbiosis
      description: >
        Determine whether reproducible microbiome shifts precede, track with,
        or follow enteric alpha-synuclein and autonomic biomarker changes.
      assays:
      - preferred_term: shotgun metagenomic sequencing
      - preferred_term: fecal metabolomics
      direction: POSITIVE
    - name: Intestinal inflammation and barrier trajectory
      target: pathophysiology#Intestinal Inflammation and Barrier Dysfunction
      description: >
        Measure whether inflammatory and permeability markers rise before
        enteric alpha-synuclein detection and clinical conversion.
      assays:
      - preferred_term: calprotectin assay
      - preferred_term: zonulin assay
      direction: POSITIVE
    - name: Enteric alpha-synuclein seeding
      target: pathophysiology#Enteric Alpha-Synuclein Seeding
      description: >
        Track phosphorylated or aggregated alpha-synuclein in standardized
        enteric biopsies as a candidate initiating event.
      assays:
      - preferred_term: immunohistochemistry
      - preferred_term: alpha-synuclein seed amplification assay
      direction: POSITIVE
    decision_criterion: >-
      Microbiome and barrier changes would support a trigger model only if they
      reproducibly precede enteric alpha-synuclein positivity and autonomic
      denervation in converters; changes that follow autonomic dysfunction would
      support a consequence or modifier model.
    would_support:
    - pathophysiology#Gut Microbiome Dysbiosis
    - pathophysiology#Intestinal Inflammation and Barrier Dysfunction
    - pathophysiology#Enteric Alpha-Synuclein Seeding
  evidence:
  - reference: PMID:34220443
    reference_title: "Serum and Fecal Markers of Intestinal Inflammation and Intestinal Barrier Permeability Are Elevated in Parkinson's Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A causal relationship has not been established, but gut dysbiosis is prevalent in PD and may lead to intestinal inflammation and barrier dysfunction."
    explanation: >-
      The human marker study states the core causal-direction uncertainty
      motivating this knowledge gap.
  - reference: PMID:36332796
    reference_title: "Gut microbiome and Parkinson's disease: Perspective on pathogenesis and treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "However, it remains unclear how these mechanisms relate to sporadic PD, a more common form of PD."
    explanation: >-
      Review-level synthesis highlights uncertainty about how gut-related
      mechanisms map onto sporadic PD pathogenesis.
  - reference: PMID:41826284
    reference_title: "Gut microbiota modulation via repeated donor fecal transplantation improves motor and gastrointestinal symptoms in drug-naïve Parkinson's disease: a randomized phase 2 trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Microbiome profiling revealed greater similarity to donor composition and a marked reduction in Escherichia-Shigella, correlating with decreased colonic α-synuclein aggregation"
    explanation: >-
      The strongest interventional human evidence bearing on this gap: in a
      72-patient phase 2 trial of repeated donor fecal transplantation the
      induced microbiome shift correlated with reduced colonic alpha-synuclein
      aggregation. A correlation between two changes measured after treatment
      does not order dysbiosis before enteric alpha-synuclein misfolding, which
      is the question this gap asks.
  - reference: PMID:41674471
    reference_title: "Safety and Efficacy of Fecal Microbiota Transplantation in Alleviating Symptoms of Parkinson's Disease: A Randomized, Placebo-Controlled, Double-Blinded Study."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "A single FMT does not influence motor symptoms manifestation in patients with PD but could improve non-motor functioning via gut-brain axis."
    explanation: >-
      The counterweight that keeps this gap open. A 59-patient randomized
      placebo-controlled trial of single colonoscopic transplantation found no
      motor effect at 12 months. Read with the positive repeated-dosing trial
      above, microbiota manipulation has inconsistent clinical effects, which is
      not what a straightforward causal-trigger model would predict.
- discussion_id: gap_pd_variant_specific_isogenic_hpsc_mechanisms
  prompt: >-
    Which Parkinson disease risk and causal variants produce convergent
    dopaminergic-neuron mechanisms in a controlled human genetic background,
    and which phenotypes are variant-specific, modifier-dependent, or culture
    artifacts?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Dopaminergic Neuron Loss
  - pathophysiology#Alpha-Synuclein Aggregation
  - pathophysiology#Mitochondrial Dysfunction
  - pathophysiology#Autophagy-Lysosome Pathway Dysfunction
  rationale: >-
    Patient-derived iPSC comparisons are powerful but confounded by background
    genetic variation. Large WGS-QC'd isogenic hPSC panels, differentiated into
    midbrain dopaminergic neurons and phenotyped with imaging and sequencing,
    can separate variant-specific causal mechanisms from shared downstream
    neurodegenerative states.
  proposed_experiments:
  - experiment_id: exp_pd_automated_isogenic_hpsc_variant_panel
    name: Automated isogenic hPSC Parkinson variant panel
    description: >-
      Generate or extend a WGS-QC'd isogenic hPSC panel carrying high-risk or
      causal Parkinson disease alleles, differentiate lines into midbrain
      dopaminergic neurons, and benchmark variant-specific effects on
      alpha-synuclein handling, mitochondrial state, lysosomal function, and
      dopaminergic-neuron survival.
    experiment_type:
      preferred_term: high-throughput isogenic stem-cell perturbation experiment
    model_systems:
    - name: Genome-edited hPSC-derived midbrain dopaminergic neuron panel
      description: >-
        Isogenic human pluripotent stem cell collection carrying Parkinson
        disease variants, differentiated into disease-relevant dopaminergic
        neurons for mechanism-resolved phenotyping.
      experimental_model_type: IPSC_DERIVED_MODEL
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      cell_types:
      - preferred_term: midbrain dopaminergic neuron
        term:
          id: CL:0000700
          label: dopaminergic neuron
      publication: PMID:38405931
      notes: >-
        Designed to be compatible with automated hPSC genome-engineering and
        clonal QC workflows such as ATTIS-style high-throughput line generation.
    perturbations:
    - name: Parkinson disease variant editing
      target: pathophysiology#Dopaminergic Neuron Loss
      description: >
        Introduce or compare causal and high-risk Parkinson alleles in a shared
        genetic background.
      genes:
      - preferred_term: SNCA
        term:
          id: hgnc:11138
          label: SNCA
      - preferred_term: LRRK2
        term:
          id: hgnc:18618
          label: LRRK2
      - preferred_term: GBA1
        term:
          id: hgnc:4177
          label: GBA
      - preferred_term: PINK1
        term:
          id: hgnc:14581
          label: PINK1
      - preferred_term: PRKN
        term:
          id: hgnc:8607
          label: PRKN
    - name: Prime-editing generation or correction
      target: gene#LRRK2
      description: >
        Use prime editing or correction to create reciprocal disease and rescue
        alleles where feasible.
      genes:
      - preferred_term: LRRK2
        term:
          id: hgnc:18618
          label: LRRK2
    readouts:
    - name: Alpha-synuclein aggregation burden
      target: pathophysiology#Alpha-Synuclein Aggregation
      description: >
        High-content imaging and biochemical readouts of alpha-synuclein
        accumulation in differentiated dopaminergic neurons.
      assays:
      - preferred_term: high-content imaging
      - preferred_term: immunocytochemistry
      direction: POSITIVE
    - name: Mitochondrial dysfunction
      target: pathophysiology#Mitochondrial Dysfunction
      description: >
        Mitochondrial respiration, membrane-potential, and stress-state
        measurements across edited variants and corrected controls.
      biological_processes:
      - preferred_term: mitochondrial organization
        term:
          id: GO:0007005
          label: mitochondrion organization
      assays:
      - preferred_term: mitochondrial respiration assay
      direction: NEGATIVE
    - name: Autophagy-lysosome pathway dysfunction
      target: pathophysiology#Autophagy-Lysosome Pathway Dysfunction
      description: >
        Lysosomal function, autophagic flux, and transcriptomic readouts
        stratified by causal allele and rescue status.
      biological_processes:
      - preferred_term: autophagy
        term:
          id: GO:0006914
          label: autophagy
      assays:
      - preferred_term: lysosomal function assay
      - preferred_term: single-cell transcriptomic profiling
      direction: NEGATIVE
    - name: Dopaminergic neuron survival and identity
      target: pathophysiology#Dopaminergic Neuron Loss
      description: >
        Cell survival, dopaminergic identity, and dopamine biosynthesis readouts
        after differentiation.
      biological_processes:
      - preferred_term: dopamine biosynthetic process
        term:
          id: GO:0042416
          label: dopamine biosynthetic process
      assays:
      - preferred_term: high-content imaging
      - preferred_term: targeted transcriptomic profiling
      direction: NEGATIVE
    controls:
    - name: Isogenic unedited parental hPSC line
      description: Same genetic background without Parkinson-associated edits.
    - name: Corrected rescue alleles
      description: Reciprocal correction of disease alleles where editing design allows.
    decision_criterion: >-
      A mechanism is prioritized when multiple independently edited clones for
      the same variant show a reproducible phenotype that is attenuated by
      isogenic correction and maps to a declared pathophysiology node.
    would_support:
    - pathophysiology#Alpha-Synuclein Aggregation
    - pathophysiology#Mitochondrial Dysfunction
    - pathophysiology#Autophagy-Lysosome Pathway Dysfunction
    - pathophysiology#Dopaminergic Neuron Loss
    would_refute:
    - pathophysiology#Alpha-Synuclein Aggregation
    - pathophysiology#Mitochondrial Dysfunction
    - pathophysiology#Autophagy-Lysosome Pathway Dysfunction
    evidence:
    - reference: PMID:38405931
      reference_title: "iSCORE-PD: an isogenic stem cell collection to research Parkinson's Disease."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "we generated a collection of 65 human stem cell lines genetically engineered to harbor high risk or causal variants in genes associated with PD"
      explanation: >-
        Demonstrates the feasibility of a large isogenic hPSC Parkinson variant
        collection for mechanism-resolved experiments.
    - reference: PMID:38405931
      reference_title: "iSCORE-PD: an isogenic stem cell collection to research Parkinson's Disease."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "rigorous quality controls, including whole-genome sequencing of each line."
      explanation: Supports WGS-QC as a design requirement for the proposed panel.
    - reference: PMID:36069759
      reference_title: "Highly efficient generation of isogenic pluripotent stem cell models using prime editing."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Finally, we demonstrated that this mRNA-based delivery approach can be used repeatedly to yield editing efficiencies exceeding 60% and to correct or introduce familial mutations causing Parkinson's disease in hPSCs."
      explanation: >-
        Supports prime editing as a practical modality for generating and
        correcting Parkinson disease mutations in hPSCs.
  evidence:
  - reference: PMID:38405931
    reference_title: "iSCORE-PD: an isogenic stem cell collection to research Parkinson's Disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our iSCORE-PD collection represents an easily accessible and valuable platform to study PD, which can be used by investigators to understand the molecular pathophysiology of PD in a human cellular setting."
    explanation: >-
      Establishes the existence of a human isogenic hPSC resource for studying
      Parkinson molecular pathophysiology, while the specific knowledge gap
      remains the standardized phenotype-to-mechanism adjudication.
- discussion_id: gap_pd_weight_loss_multifactorial_mechanisms
  prompt: >-
    Weight loss is a long-observed non-motor symptom of Parkinson disease, yet
    its mechanisms remain incompletely understood. Which of the proposed pathways
    — metabolic dysregulation, neuroendocrine disruption, gastrointestinal
    dysfunction, cognitive decline, and pharmacologic effects — are primary drivers
    versus secondary consequences, and how do they interact across the disease course?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Dopaminergic Neuron Loss
  - pathophysiology#Intestinal Inflammation and Barrier Dysfunction
  - pathophysiology#Basal Ganglia Circuit Dysfunction
  rationale: >-
    Weight loss exerts substantial morbidity and mortality in PD, yet limited
    mechanistic understanding constrains treatment options. The Gabriel et al.
    (2026) review identifies six interacting pathways: (1) metabolic
    dysregulation (altered energy expenditure or intake), (2) neuroendocrine
    disruption (leptin/ghrelin/GLP-1 signaling), (3) gastrointestinal
    dysfunction (dysmotility, malabsorption, barrier dysfunction), (4) cognitive
    decline (reduced appetite awareness), (5) dopaminergic-medication effects
    (appetite suppression), and (6) brain stimulation paradoxes (DBS-induced
    weight changes). The relative contribution and temporal ordering of these
    mechanisms remain unknown. Resolving cross-mechanism interactions would
    enable targeted metabolic interventions in PD.
  proposed_experiments:
  - experiment_id: exp_pd_weight_loss_longitudinal_mechanisms
    name: Longitudinal weight loss phenotype stratification with multi-mechanism readouts
    description: >-
      Follow a large PD cohort with serial body composition (DXA, bioimpedance),
      resting metabolic rate, circulating metabolic hormones (leptin, adiponectin,
      GLP-1, ghrelin), dopamine-agonist doses and appetite-affecting medications,
      cognitive testing, gastrointestinal symptom questionnaires, and GI transit
      imaging. Stratify the cohort into weight-loss phenotypes (progressive vs.
      stable) and identify mechanistic signatures.
    experiment_type:
      preferred_term: longitudinal multi-omics observational cohort study
    readouts:
    - name: Metabolic rate and body composition trajectories
      target: pathophysiology#Dopaminergic Neuron Loss
      description: >
        Measure resting metabolic rate, energy expenditure, and changes in
        lean vs. fat mass to distinguish metabolic dysregulation from
        reduced intake.
      assays:
      - preferred_term: indirect calorimetry
      - preferred_term: dual-energy X-ray absorptiometry
      direction: NEGATIVE
    - name: Circulating neuroendocrine hormone patterns
      target: pathophysiology#Dopaminergic Neuron Loss
      description: >
        Quantify leptin, ghrelin, adiponectin, GLP-1, and other appetite-regulating
        hormones to identify dysregulation of satiety/hunger signaling.
      assays:
      - preferred_term: serum hormone quantification
      direction: NEGATIVE
    - name: Gastrointestinal function and symptoms
      target: pathophysiology#Intestinal Inflammation and Barrier Dysfunction
      description: >
        Assess gastric emptying (breath test), small-bowel transit, colonic
        function, permeability markers (zonulin, calprotectin), and GI symptom
        severity to establish causal vs. consequential GI involvement.
      assays:
      - preferred_term: gastric-emptying scintigraphy
      - preferred_term: fecal calprotectin assay
      direction: NEGATIVE
    - name: Cognitive decline severity
      target: pathophysiology#Basal Ganglia Circuit Dysfunction
      description: >
        Administer validated cognitive batteries (MoCA, MMSE) and assess
        appetite awareness to test the cognitive-suppression hypothesis.
      assays:
      - preferred_term: cognitive assessment battery
      direction: NEGATIVE
    decision_criterion: >-
      Mechanistic dominance is supported by: (1) trajectories preceding or
      independent of weight loss (dysmetabolism, hormone changes, GI dysfunction);
      (2) stratification of the cohort into mechanistically distinct weight-loss
      phenotypes; (3) reproducible associations between mechanism-specific markers
      and subsequent weight-loss progression in converters.
    would_support:
    - pathophysiology#Dopaminergic Neuron Loss
    - pathophysiology#Intestinal Inflammation and Barrier Dysfunction
    - pathophysiology#Basal Ganglia Circuit Dysfunction
  evidence:
  - reference: PMID:41781031
    reference_title: "When the Scale Drops: Pathways to Weight Loss in Parkinson's Disease and Future Directions."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "weight loss has long been observed in PD and other neurodegenerative disorders, yet the mechanisms remain incompletely understood. This limited mechanistic insight has left few treatment options for weight loss in PD."
    explanation: >-
      The Gabriel et al. review establishes weight loss as a significant yet
      mechanistically unexplained PD symptom, directly motivating this knowledge gap.
  - reference: PMID:41781031
    reference_title: "When the Scale Drops: Pathways to Weight Loss in Parkinson's Disease and Future Directions."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Emerging research highlights the role of metabolic regulation, neuroendocrine signaling, pharmacologic treatment, cognitive decline, gastrointestinal dysfunction, and brain stimulation in shaping weight trajectories in PD."
    explanation: >-
      This enumerates the six candidate mechanisms for weight loss in PD,
      supporting the multi-pathway framing of the gap.
- discussion_id: gap_pd_origin_site_operationalization
  prompt: >-
    Can brain-first versus body-first origin site be operationalized as a
    measurable layer of the biological staging frameworks for Parkinson
    disease, and does origin-site stratification carry mechanistic or
    prognostic information that the existing anchors and data-driven subtypes
    do not already capture?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - mechanistic_hypotheses#body_first_enteric_alpha_synuclein_model
  - mechanistic_hypotheses#brain_first_central_alpha_synuclein_model
  rationale: >-
    Both origin-site hypotheses in this entry are curated as ALTERNATIVE, and
    both are assigned in practice from proxies - premotor REM-sleep behavior
    disorder, autonomic markers, imaging asymmetry - rather than from an
    observed first site of alpha-synuclein pathology. Two current biological
    definitions of the disease, the neuronal alpha-synuclein disease integrated
    staging system and SynNeurGe, are built on alpha-synuclein seeding,
    neurodegeneration, genetics, and functional impairment; neither carries an
    origin-site axis. That is an implementation gap rather than evidence against
    either model, and it should not be read as a scientific qualification of the
    mechanism. But it leaves the practical question unanswered: no consensus
    operational definition of origin site exists, so origin-site subtype
    membership is not portable between cohorts, and there is no agreed way to
    record it alongside a biological stage. The prognostic side of the question
    is not favorable either - a 10-year PPMI comparison found that data-driven
    subtypes separate rapid progressors more efficiently than the pathological
    brain-first/body-first labels do. That comparison measures prognostic
    enrichment, not anatomical origin, so it does not test either mechanism; it
    does mean the case for adding an origin-site layer has to rest on
    mechanistic rather than prognostic grounds.
  evidence:
  - reference: PMID:38267190
    reference_title: "A biological definition of neuronal α-synuclein disease: towards an integrated staging system for research."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Our biological definition establishes a staging system, the neuronal α-synuclein disease integrated staging system (NSD-ISS), rooted in the biological anchors (S and D) and the degree of functional impairment caused by clinical signs or symptoms."
    explanation: >-
      Names the anchors of the NSD-ISS - alpha-synuclein seeding, dopaminergic
      dysfunction, and functional impairment - none of which encodes where
      pathology began, which is the gap this discussion records.
  - reference: PMID:39973492
    reference_title: "SynNeurGe: The road ahead for a biological definition of Parkinson's disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "However, SynNeurGe provides a broader, more flexible framework that integrates α-synuclein pathology (S), neurodegeneration (N), and genetics (G), linked to clinical features (C)."
    explanation: >-
      The competing biological classification is organized on the same kind of
      axes, so the absence of an origin-site layer is common to both frameworks
      rather than particular to one.
  - reference: PMID:42286020
    reference_title: "Comparative analysis of progression milestones across Parkinson's disease clinical, pathological, and data-driven subtypes: a 10-year follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Data-driven subtypes exhibited the highest progression rates, with DM patients attaining 63.0% of milestones, surpassing PIGD (55.6%) and body-first (54.0%) subtypes."
    explanation: >-
      Quantifies the prognostic half of the gap in the PPMI cohort: the
      body-first label is outperformed by a data-driven subtype for identifying
      rapid progressors. This bears on the utility of origin-site stratification
      for trial design, not on whether central or peripheral initiation occurs.
  notes: >-
    Recorded from the 2026 OpenScientist hypothesis-search reports for both
    origin-site models, which independently raise the missing origin-site layer
    as a curation-level knowledge gap. The two staging-framework citations and
    the progression-milestone comparison ground claims that the
    mechanistic_hypotheses notes previously asserted without references. An
    earlier preprint of the milestone comparison (PMID:40678221) reported lower
    milestone proportions (50%, 43%, 42%) than the final publication cited here;
    cite the published version.

- discussion_id: pd_brain_to_gut_tight_junction_translation
  prompt: >-
    Does nigrostriatal dopaminergic degeneration produce a functionally leaky
    intestinal barrier in human Parkinson disease, given that two independent
    6-hydroxydopamine rat studies report reduced zona occludens-1 with raised
    circulating lipopolysaccharide, while human colonic biopsies show
    disorganized tight junction morphology and yet no measurable change in
    para- or transcellular permeability?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Intestinal Tight Junction Protein Loss
  - pathophysiology#Striatal Dopamine Deficiency
  - pathophysiology#Intestinal Inflammation and Barrier Dysfunction
  rationale: >-
    The model evidence for a brain-to-gut arm is consistent and comes from two
    laboratories: lesioning the nigrostriatal dopaminergic system in rats lowers
    zona occludens-1 in colon and ileum, raises circulating lipopolysaccharide
    and intestinal fatty acid-binding protein, and shifts the microbiome. The
    human comparison has to be read carefully, because the two literatures do
    not measure the same thing. In colonic biopsies from 31 people with
    Parkinson disease, the protein reported as unchanged is zona occludens-1 by
    immunoblot on whole-biopsy lysate, whereas the reduced protein, occludin,
    was also assayed that way. By immunofluorescence, which is the modality both
    rodent studies used, the same cohort is clearly abnormal: a normal reticular
    pattern of occludin and zona occludens-1 staining was present in 6 of 8
    controls but only 9 of 31 patients, and frankly disrupted morphology in 1 of
    8 controls against 14 of 31 patients. So on the matched modality, human and
    rat agree that the junction is abnormal, and the apparent zona occludens-1
    contradiction is at least partly a question of whether total abundance or
    spatial organization is being measured. What does not dissolve this way, and
    is the real content of this mismatch, is the functional result. Neither
    paracellular nor transcellular permeability differed from controls, while
    the rodent readouts predict a measurable leak. Three explanations are not
    distinguished by the present data. The measurements may simply be
    non-equivalent, since a junction can be visibly disorganized without losing
    enough barrier function to register as flux across a biopsy in an Ussing
    chamber. The rodent lesion is acute and unilateral where human nigrostriatal
    loss is gradual and partial, so the rat may model a rate rather than a
    state. Or the human intestine compensates, restoring function around an
    altered junctional architecture. One explanation can be set aside: this is
    not a levodopa artifact, because the authors found moderate to severe
    junctional disorganization in the five patients who had never received
    levodopa and no correlation between cumulative dose and the severity of
    altered permeability. Recording this as a HUMAN_MODEL_MISMATCH rather than a
    KNOWLEDGE_GAP is deliberate. The evidence is not absent on either side; it
    exists in both, and it is the translational validity of the rodent
    functional readout that is open. Note also what this mismatch does not
    touch. The brain-to-gut direction is a claim about a consequence of
    established dopaminergic loss and is independent of the brain-first versus
    body-first debate over where alpha-synuclein pathology begins, which is why
    the new edges carry no hypothesis group. The 6-hydroxydopamine model
    produces no alpha-synuclein pathology in the brain at all, so it cannot
    speak to that question.
  proposed_experiments:
  - experiment_id: exp_pd_junctional_panel_by_disease_stage
    name: Stage-stratified colonic tight junction panel in Parkinson disease
    description: >-
      Measure the junctional panel three ways in the same colonic biopsies, by
      immunoblot for total abundance, by immunofluorescence for spatial
      organization, and by flux for paracellular permeability, stratified by
      disease duration and including de novo patients and a prodromal group
      defined by REM sleep behavior disorder. Assaying all three on one specimen
      is the point, since the existing human study measured zona occludens-1
      abundance and occludin abundance by immunoblot and organization by
      immunofluorescence, leaving the modality and the protein confounded.
    experiment_type:
      preferred_term: stage-stratified observational biopsy study
    decision_criterion: >-
      If organization is disrupted while abundance and flux are normal at every
      stage, the discordance is a measurement-equivalence result and the rodent
      abundance readout simply does not correspond to the human one. If flux
      rises in early or prodromal disease and normalizes later, the negative
      finding in established disease is a sampling-time artifact and the rodent
      model translates to a window. If flux is normal at every stage despite
      disrupted organization, human compensation is the surviving explanation.
  - experiment_id: exp_pd_dopaminergic_lesion_gradient_gut_barrier
    name: Graded nigrostriatal lesion versus gut barrier response
    description: >-
      Titrate nigrostriatal dopaminergic loss across a graded range in a rodent
      model, from partial loss comparable to early human disease up to the
      lesion extent used in existing 6-hydroxydopamine studies, reading out the
      full junctional protein panel and functional permeability at each level.
    experiment_type:
      preferred_term: dose-response perturbation study
    decision_criterion: >-
      If junctional and permeability change appear only above a lesion threshold
      steeper than human disease reaches, the human negative result is explained
      by lesion severity rather than by species. A barrier response at partial
      lesion levels would leave the species difference as the remaining
      explanation.
  evidence:
  - reference: PMID:25775153
    reference_title: "Structural alterations of the intestinal epithelial barrier in Parkinson's disease."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "By contrast to occludin, no change in ZO-1 expression levels was observed in PD"
    explanation: >-
      Refutes the specific rodent claim that zona occludens-1 abundance falls in
      Parkinson disease colon. The measurement is an immunoblot on whole-biopsy
      lysate, which is the modality qualification this discussion turns on.
  - reference: PMID:25775153
    reference_title: "Structural alterations of the intestinal epithelial barrier in Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TJs morphology was disrupted and irregularly distributed in the mucosa of 1 out of 8 controls"
    explanation: >-
      The other half of the same paper, split into its own item because it cuts
      the opposite way. By immunostaining, the modality the rodent studies used,
      junctional morphology is disrupted in 14 of 31 patients against 1 of 8
      controls, so the human junction is abnormal after all.
  - reference: PMID:25775153
    reference_title: "Structural alterations of the intestinal epithelial barrier in Parkinson's disease."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "The para- and transcellular permeability were not different between PD patients and controls."
    explanation: >-
      The functional counterpart of the same mismatch. The rodent model predicts
      a measurable leak, and this cohort did not show one by either route.
  - reference: PMID:25775153
    reference_title: "Structural alterations of the intestinal epithelial barrier in Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "moderate to severe TJs disorganization in the 5 patients who had never received levodopa, suggesting that the altered TJs morphology was not related to chronic levodopa intake"
    explanation: >-
      Rules out medication as the explanation for the human junctional finding,
      which is why this discussion does not offer levodopa exposure as one of
      the candidate accounts of the mismatch.
  - reference: PMID:42732868
    reference_title: "Striatal 6-hydroxydopamine lesion in rats induces dysregulation of the gut barrier."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "the specific contribution of nigrostriatal injury to these outcomes is unknown"
    explanation: >-
      The authors' own framing of the gap this discussion records, written before
      their experiment and still true of the human case afterwards.
  - reference: PMID:37271045
    reference_title: "Nigrostriatal 6-hydroxydopamine lesions increase alpha-synuclein levels and permeability in rat colon."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "It exerts no aSyn pathology in the brain, but changes in the gut have not been assessed."
    explanation: >-
      Documents that the 6-hydroxydopamine model carries no brain alpha-synuclein
      pathology, which is why these brain-to-gut edges are not attached to the
      brain-first hypothesis group.
  notes: >-
    Raised from dismech issue #12152 ([kgap-scan] Parkinson's Disease:
    dopaminergic neurodegeneration and gut barrier dysfunction mechanism), which
    asked whether pathophysiology nodes should be added for dopamine-dependent
    regulation of gut barrier integrity. They were, as Intestinal Tight Junction
    Protein Loss plus two edges out of Striatal Dopamine Deficiency. This
    discussion records the human evidence that does not line up with them.
computational_models:
- name: Alpha-Synuclein Aggregation BST Model
  description: >
    Biochemical Systems Theory (BST) model of alpha-synuclein aggregation kinetics
    in dopaminergic neurons. Integrates dopamine metabolism, ubiquitin-proteasome
    system, and lysosomal degradation pathways. Simulates effects of oxidative
    stress and proteasome inhibition on synuclein accumulation.
  modeled_mechanisms:
  - target: Alpha-Synuclein Aggregation
    description: Models alpha-synuclein aggregation kinetics and degradation-pathway effects in dopaminergic neurons.
  model_type: KINETIC
  repository_url: https://www.ebi.ac.uk/biomodels/BIOMD0000000575
  model_id: BIOMD0000000575
  publication: PMID:19136028
  notes: First comprehensive kinetic model of PD-related protein aggregation
- name: Whole Dopaminergic Neuron SBML Model
  description: >
    Large-scale Systems Biology Markup Language (SBML) model of dopaminergic
    neuron containing 139 reactions and 111 metabolites. Captures dopamine
    synthesis, vesicular storage, release, reuptake, and degradation alongside
    mitochondrial function and oxidative stress.
  modeled_mechanisms:
  - target: Striatal Dopamine Deficiency
    description: Models dopamine synthesis, storage, release, reuptake, and degradation in dopaminergic-neuron physiology.
  - target: Mitochondrial Dysfunction
    description: Models mitochondrial metabolism alongside dopamine handling in dopaminergic neurons.
  model_type: KINETIC
  repository_url: https://www.ebi.ac.uk/biomodels/MODEL1302200000
  model_id: MODEL1302200000
  publication: PMID:24196439
  model_format: SBML
  notes: Enables simulation of drug effects on dopaminergic neurotransmission
- name: Basal Ganglia Spiking Neural Network
  description: >
    Computational model of the basal ganglia circuit capturing dopamine-modulated
    dynamics between striatum, globus pallidus, subthalamic nucleus, and
    substantia nigra. Simulates pathological beta-band oscillations and motor
    dysfunction in PD.
  modeled_mechanisms:
  - target: Basal Ganglia Circuit Dysfunction
    description: Models dopamine-modulated basal ganglia circuit dynamics, beta-band oscillations, and DBS effects.
  model_type: PHYSIOLOGICAL
  publication: PMID:29666208
  notes: Models circuit-level effects of dopamine depletion and DBS therapy
- name: Alpha-Synuclein Prion-like Spreading Model
  description: >
    Network diffusion model simulating prion-like propagation of misfolded
    alpha-synuclein through brain connectome. Uses graph-theoretical approach
    to predict spatial patterns of neurodegeneration from initial seeding sites.
  modeled_mechanisms:
  - target: Alpha-Synuclein Aggregation
    description: Models connectome-based propagation of misfolded alpha-synuclein pathology.
  model_type: AGENT_BASED
  notes: Predicts Braak staging patterns from connectivity-based spreading
- name: PD Map Cohort-Specific Probabilistic Boolean Models
  description: >-
    Probabilistic Boolean Networks (PBNs) built from the Parkinson's disease map, the
    largest curated repository of PD pathway diagrams. Pathways enriched in the
    Parkinson's Progression Markers Initiative (PPMI) cohort were exported from the PD
    map in CellDesigner SBML format, translated to SBML-qual with CaSQ, and
    parameterised against cohort miRNA and transcriptomic data so that each model
    represents a specific PD subgroup (prodromal, SWEDD, parkinsonism). Simulating the
    resulting models with pyMaBoSS reveals subtype-specific differences in dopamine
    transcription, PI3K/AKT signalling, FOXO3 activity, mTOR-MAPK signalling and PRKN
    mitophagy. The probabilistic parameterisation, rather than plain Boolean logic, is
    what lets cohort-level data enter the model.
  model_type: BOOLEAN_NETWORK
  model_format: SBML-qual
  model_software: CaSQ, pyMaBoSS, CellDesigner
  repository_url: https://gitlab.lcsb.uni.lu/lcsb-biocore/publications/hemedan23-boolean-modelling-of-pd
  publication: PMID:39429779
  modeled_mechanisms:
  - target: Autophagy-Lysosome Pathway Dysfunction
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    divergences:
    - divergence_type: PROXY_QUANTITY
      materiality: QUALIFYING
      description: >-
        The model represents transcriptional regulation of the autophagy-lysosome
        pathway. The node describes the degradative process itself -- flux through
        that pathway -- which transcript abundance constrains but does not measure.
    - divergence_type: CALIBRATION_PROVENANCE
      materiality: QUALIFYING
      description: >-
        Node transition probabilities were fitted to cohort-level miRNA and
        transcriptomic data, not to any direct assay of autophagic flux.
    - divergence_type: SCALE_EXTRAPOLATION
      materiality: QUALIFYING
      description: >-
        A molecular signalling network standing for a cell-scale degradative
        process.
    description: >-
      PRKN mitophagy is one of the enriched PD map pathways converted into a
      cohort-parameterised Boolean model, and autophagy/mitophagy activity is one of
      the axes on which the subtypes separate.
    limitations: >-
      The model is parameterised from cohort-level miRNA and transcriptomic data rather
      than from direct measurement of autophagic flux, so it represents transcriptional
      regulation of the pathway rather than the degradative process itself.
    readouts:
    - name: PRKN-mitophagy model activity across PD subgroups
      target: Autophagy-Lysosome Pathway Dysfunction
      direction: ALTERED
      interpretation: >-
        Mitophagy and autophagy activities differ between the SWEDD, prodromal and
        parkinsonism subgroups rather than moving in one direction across all of PD.
      evidence:
      - reference: PMID:39429779
        reference_title: "Cohort-specific boolean models highlight different regulatory modules during Parkinson's disease progression."
        supports: SUPPORT
        evidence_source: COMPUTATIONAL
        snippet: >-
          differences in autophagy and mitophagy activities were observed, suggesting
          unique disease mechanisms within each PD subtype
        explanation: >-
          Reports the subtype-dependent autophagy/mitophagy readout this link records.
    evidence:
    - reference: PMID:39429779
      reference_title: "Cohort-specific boolean models highlight different regulatory modules during Parkinson's disease progression."
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: >-
        The enriched pathways included dopamine transcription pathways, PI3k/AKT
        signaling, FOXO3 activity, mTOR-MAPK signaling, and PRKN mitophagy
      explanation: >-
        Names PRKN mitophagy among the pathways modelled, linking this model to the
        autophagy-lysosome node.
  - target: Striatal Dopamine Deficiency
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: MOLECULAR
    divergences:
    - divergence_type: PROXY_QUANTITY
      materiality: INVALIDATING
      description: >-
        The model's quantity is transcriptional regulation of dopamine-synthesis
        genes. The node's quantity is dopamine concentration in the striatum.
        These are different measurements separated by transcription, translation,
        synthesis, transport and terminal survival, and the model cannot be read
        as reporting the second. This is the divergence behind the link's LOW
        fidelity, and it is invisible to the scale comparison alone.
    - divergence_type: BOUNDARY_OMISSION
      materiality: QUALIFYING
      description: >-
        Nigrostriatal terminal loss and the presynaptic deficit that clinically
        defines this node are not in the model.
    - divergence_type: SCALE_EXTRAPOLATION
      materiality: QUALIFYING
      description: >-
        Two scale steps: a molecular network inferring the dopaminergic tone of an
        anatomical structure.
    - divergence_type: CALIBRATION_PROVENANCE
      materiality: QUALIFYING
      description: >-
        Parameterised from cohort-level omics rather than from striatal dopamine
        measurement in the cohorts the model stratifies.
    description: >-
      Dopamine transcription pathways are among the enriched PD map diagrams converted
      to Boolean models and show distinct behaviour across subtypes.
    limitations: >-
      The model represents transcriptional regulation of dopamine synthesis in a
      cohort-parameterised signalling network; it does not represent striatal dopamine
      concentration, nigrostriatal terminal loss, or the presynaptic deficit that
      defines this node clinically.
    evidence:
    - reference: PMID:39429779
      reference_title: "Cohort-specific boolean models highlight different regulatory modules during Parkinson's disease progression."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: COMPUTATIONAL
      snippet: >-
        These models revealed distinct behaviors in key molecular pathways across PD
        subtypes, including dopamine transcription, PI3K/AKT signaling, FOXO3 activity,
        mTOR-MAPK signaling, and PRKN mitophagy
      explanation: >-
        Supports a transcription-level dopamine claim. Indirect: the quote asserts
        subtype-specific behaviour of dopamine-transcription pathways, and striatal
        dopamine deficiency follows only by an inference step across transcription,
        synthesis and terminal survival -- which is also why fidelity here is LOW.
  findings:
  - statement: >-
      Cohort-level and real-world patient data were integrated into the logical models
      to represent subtype-specific pathway deregulation.
    evidence:
    - reference: PMID:39429779
      reference_title: "Cohort-specific boolean models highlight different regulatory modules during Parkinson's disease progression."
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: >-
        By integrating cohort-level and real-world patient data, we modeled PD's
        subtype-specific pathway deregulations, providing a refined representation of
        its molecular landscape
      explanation: States the data-integration step that makes these models cohort-specific.
  evidence:
  - reference: PMID:39429779
    reference_title: "Cohort-specific boolean models highlight different regulatory modules during Parkinson's disease progression."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      we employed systems medicine approaches using the PD map, a detailed repository
      of PD-related interactions and applied Probabilistic Boolean Networks (PBNs) to
      capture the stochastic nature of molecular dynamics
    explanation: >-
      Establishes the PD map as the knowledge source and PBNs as the modelling
      formalism for this entry.
  - reference: PMID:39429779
    reference_title: "Cohort-specific boolean models highlight different regulatory modules during Parkinson's disease progression."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      The pathways identified via the enrichment analysis were exported from the PD map
      in CellDesigner SBML format and translated into SBML-qual files by the CaSQ tool
    explanation: >-
      Documents the CaSQ map-to-model translation and the SBML-qual format recorded in
      model_format.
  notes: >-
    Curated as part of the Boolean/logical modelling track; see
    docs/superpowers/plans/2026-08-28-boolean-modeling-and-pathographs.md.
    Literature-referenced, not runnable in-repo: dismech-perturb has no SBML-qual
    execution path yet. Note this is a *probabilistic* Boolean network — cohort data enter as node
    transition probabilities, so it is not a plain deterministic Boolean model.
references:
- reference: PMID:20301402
  title: Monogenic Parkinson Disease Overview.
  tags:
  - GeneReviews
  findings: []
- reference: PMID:33983693
  title: DNAJC6 Parkinson Disease.
  tags:
  - GeneReviews
  findings: []
- reference: DOI:10.2147/ndt.s540718
  title: Updates on Parkinson’s Disease
  findings: []
- reference: DOI:10.3389/fnagi.2025.1617106
  title: 'Understanding Parkinson’s disease: current trends and its multifaceted complications'
  findings: []
- reference: DOI:10.3390/cells14151161
  title: 'Parkinson’s Disease: Bridging Gaps, Building Biomarkers, and Reimagining Clinical Translation'
  findings: []
- reference: DOI:10.3390/ijms25137183
  title: 'A Comprehensive Approach to Parkinson’s Disease: Addressing Its Molecular, Clinical, and Therapeutic Aspects'
  findings: []
- reference: PMID:42646502
  title: "Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward."
  findings: []

📚

References & Deep Research

References

PMID:20301402

Monogenic Parkinson Disease Overview.

No top-level findings curated for this source.

PMID:33983693

DNAJC6 Parkinson Disease.

No top-level findings curated for this source.

DOI:10.2147/ndt.s540718

Updates on Parkinson’s Disease

No top-level findings curated for this source.

DOI:10.3389/fnagi.2025.1617106

Understanding Parkinson’s disease: current trends and its multifaceted complications

No top-level findings curated for this source.

DOI:10.3390/cells14151161

Parkinson’s Disease: Bridging Gaps, Building Biomarkers, and Reimagining Clinical Translation

No top-level findings curated for this source.

DOI:10.3390/ijms25137183

A Comprehensive Approach to Parkinson’s Disease: Addressing Its Molecular, Clinical, and Therapeutic Aspects

No top-level findings curated for this source.

PMID:42646502

Parkinson's Disease: Pathophysiology, Treatment Strategies, Wellness Approaches, and Obstacles/Paths Forward.

No top-level findings curated for this source.

Deep Research

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Evaluations and curation notes (2)

Extend environmental exposures with verified epidemiology and nulls · 2026-10-25T01:33:55Z · View source

Rewrote the environmental section from three sparse entries to twelve, the ten new or extended ones each carrying their own mechanism link with link-level evidence. Extended: Pesticide Exposure gains the paraquat meta-analysis (PMID:30474499), the AGRICAN agricultural cohort (PMID:29136149), the glove-use modification study (PMID:25461423) and the organochlorine meta-analysis (PMID:39520734); the AGRICAN rotenone sentence was added to the existing Mitochondrial Dysfunction link because it is the one place the human epidemiology and the rat complex I work name the same molecule. Rural Living gains the classic positive meta-analysis (PMID:11437458) and the Bradford-Hill weight-of-evidence assessment that finds the proxy associations inconsistent (PMID:27055126, graded REFUTE), and is deliberately left with no mechanism link. Head Trauma gains the population-based null (PMID:30396335, graded REFUTE) beside the existing positive meta-analysis. New: Chlorpyrifos Exposure (the only pesticide with a reported autophagic rather than mitochondrial mechanism, linked to Autophagy-Lysosome Pathway Dysfunction on the zebrafish rescue experiments), Trichloroethylene Exposure (Camp Lejeune), Ambient Fine Particulate Matter, Lead Exposure, Dairy Consumption, Helicobacter pylori Infection, Truncal Vagotomy (PROTECTS_AGAINST Vagal-Brainstem Alpha-Synuclein Propagation, the closest thing in the human literature to an experimental test of that route), Cigarette Smoking and Caffeine Consumption (both PROTECTS_AGAINST, both recorded with the reverse-causation objection). Nulls curated as content rather than omitted: nine common infections unrelated to risk, metals other than lead, and the TBI population-based null. Manganese is explicitly not curated, because the metals meta-analysis found it null for idiopathic disease and manganism is a distinct toxicant parkinsonism. Most links are PREDISPOSES with INDIRECT_UNKNOWN_INTERMEDIATES, following the existing Head Trauma precedent: nearly all of this literature is risk epidemiology with no mechanistic arm, and pointing such a study at a mechanism node would assert a route it does not measure. Only pesticides (rat complex I) and chlorpyrifos (zebrafish autophagy) carry TRIGGERS/DIRECT, and both say in the link description that the mechanism is established in the model and not in human disease. The AGRICAN snippet is bridged with " ... " across a bracketed span the reference validator strips; the explanation says so and does not restate the stripped figures. Not curated, though verified and available: ibuprofen (PMID:21368281), the beta-2 adrenoreceptor agonist work (PMID:28860381) and physical activity (PMID:25410713). These are medications and a lifestyle factor rather than environmental exposures, and were held back as a scope decision rather than for want of evidence. Provider: OpenScientist (autonomous mode, 5 iterations, 52 citations, 20 minutes). The report is committed at research/Alpha_Synucleinopathies-environmental-exposures-deep-research-openscientist.md with its citations sidecar and HTML/PDF artifacts. Falcon was unavailable for this run (the configured Edison key returns 403), so no second provider corroborates it. Every quoted sentence was read from the cached abstract in references_cache/ rather than from the report, and several of the report's figures were corrected or qualified against source in the process. The report was treated as a lead throughout.

Add brain-to-gut barrier arm from nigrostriatal dopaminergic loss · 2026-09-23T02:30:42Z · View source

Addresses issue #12152, which asked whether pathophysiology nodes should be added for dopamine-dependent regulation of gut barrier integrity. The entry already carried a gut-to-brain (body-first) chain: Gut Microbiome Dysbiosis -> Intestinal Inflammation and Barrier Dysfunction -> Enteric Alpha-Synuclein Seeding -> Vagal-Brainstem Propagation -> Alpha-Synuclein Aggregation -> Dopaminergic Neuron Loss -> Striatal Dopamine Deficiency. What was missing was the return arrow. Added: 1. New pathophysiology node 'Intestinal Tight Junction Protein Loss' (biological_scale MOLECULAR), bound to GO:0120193 tight junction organization with modifier DECREASED, CL:0002563 intestinal epithelial cell, and UBERON:0001155 colon plus UBERON:0002116 ileum. It carries a negative result as evidence (villin/brush border unchanged) which narrows the node to the junctional compartment rather than generalized enterocyte injury. Downstream to the existing 'Intestinal Inflammation and Barrier Dysfunction' node via the LPS/iFABP translocation readouts. 2. Two downstream edges out of 'Striatal Dopamine Deficiency', to the new node and to 'Gut Microbiome Dysbiosis', both causal_link_type INDIRECT_UNKNOWN_INTERMEDIATES because neither lesion study identifies the mediating route. These close a feedback loop with the body-first chain; deliberate cycles of this kind are present in 55 other disorder entries. 3. A HUMAN_MODEL_MISMATCH discussion (pd_brain_to_gut_tight_junction_translation) recording that the rodent result does not transfer cleanly. In human colonic biopsies (PMID:25775153, 31 patients) occludin rather than ZO-1 is reduced and neither para- nor transcellular permeability differs from controls, though both proteins are mislocalized. Two human-study evidence items are graded supports: REFUTE, which is established usage for a directly contradicting result (36 such items KB-wide on HUMAN_MODEL_MISMATCH discussions). The discussion names three non-distinguished explanations (lesion acuity, sampling stage/medication, species difference) and proposes two experiments with decision criteria. The new edges deliberately carry NO hypothesis_groups. The brain-first hypothesis in this entry is specifically about where alpha-synuclein pathology initiates, and the 6-OHDA model produces no brain alpha-synuclein pathology at all (stated in PMID:37271045), so tagging these edges brain-first would misattribute them. Evidence: PMID:42732868 (the paper named in the issue; 6-OHDA rat, MODEL_ORGANISM), PMID:37271045 (independent 2023 replication from a different group, MODEL_ORGANISM), PMID:25775153 (human colonic biopsy study, HUMAN_CLINICAL). All eleven snippets were verified as exact normalized substrings of the cached references before insertion. Deep research: 'just dr_fallback=--fallback research-disorder falcon Parkinsons_Disease' was run because EDISON_API_KEY/FUTUREHOUSE_API_KEY were not configured. Falcon failed with ProviderNotConfiguredError and openscientist produced the report, which is recorded in the report frontmatter (fell_back: true, requested_provider: falcon) and in its filename after running scripts/align_research_provider.py. The report covers the gut-to-brain direction (finding F008) and does not address the reverse arm, which corroborates the gap the issue describes; no claim in this change is sourced from it. The previously committed falcon report was transiently overwritten by the run and was restored from git untouched. Validation: just validate, just validate-terms, just check-entity-refs, just check-causal-targets, just check-duplicate-keys, just check-folded-hyphens, just check-snippet-length, just check-title-snippets and just check-snippet-grading all pass. just validate-disorders run over the changed file. Snippet verification reported 242/248 with 6 skipped by prefix, none of them from this change. Not changed, and pre-existing: just check-genereviews reports seven untagged GeneReviews chapters for this entry. All seven are gene-specific monogenic Parkinson chapters (LRRK2, VPS35, RAB32, PRKN, PINK1, DNAJC6, plus the Monogenic Overview) and this entry is category Complex with separate sibling entries for those genes, so they are not this entry's baseline. The check is advisory and exits 0. Left for a separate decision rather than widened into this change. Report validation (retro-fitted with just validate-research-reference and just validate-research-terms, since the openscientist run wrote no validation frontmatter). References: 50/50 resolved, 0 unresolved, 1/1 quoted claim verified, 0 off topic. Terms: 0 unresolved, but 3 named as a different term, including CHEBI:27958, which the report calls 'nicotine/tobacco' and CHEBI calls cocaine, and CHEBI:8148, which is obsolete. None of those identifiers is bound anywhere in this change. The four bindings added here (GO:0120193, CL:0002563, UBERON:0001155, UBERON:0002116) were each read from a local OAK lookup at the time of writing, not taken from the report. Deliberately left out of the commit: the report reference validation fetched roughly 47 further references into references_cache/ and upgraded two already-tracked cache files (PMID_24136244, PMID_34210995) from abstract to full text. Those two were reverted and the untracked remainder was not staged, since none is cited by this entry and the repository convention is to commit the caches the KB entry actually cites. Pre-PR red-team review round (self-review before opening the PR, findings acted on in the same commit). The review read the cached full text of PMID:25775153, which is cached as full_text_xml rather than abstract only, and found that the first draft's framing of the mismatch was wrong in two ways. First, the draft offered levodopa exposure as one of three candidate explanations. The paper tested that and argues against it: moderate to severe junctional disorganization was present in the five patients who had never received levodopa, and no correlation was found between cumulative dose and severity of altered permeability. That explanation was removed and the finding is now cited as its own evidence item. Second, and more substantively, the draft treated 'human ZO-1 unchanged' as a flat contradiction of the rodent result. It is largely a modality difference. The human ZO-1 null is an immunoblot on whole-biopsy lysate; by immunofluorescence, which is the modality both rodent studies used, the same cohort is abnormal (normal reticular staining in 6 of 8 controls against 9 of 31 patients; disrupted morphology in 1 of 8 controls against 14 of 31 patients). On the matched modality human and rat agree. The discussion's central claim was therefore narrowed to the functional permeability discordance, which carries no such confound, and measurement non-equivalence was added as a candidate explanation. The prompt, rationale and both experiment decision criteria were rewritten accordingly, and the first experiment now assays abundance, organization and flux on one specimen because the existing human study left modality and protein confounded. Three further findings were fixed. An evidence item that said 'Refutes ... while still supporting ...' was split into a REFUTE on the ZO-1 immunoblot null and a SUPPORT on the immunofluorescence disruption counts, per the CLAUDE.md rule that one item may not make two opposite claims. The PMID:37271045 item on the tight junction edge quoted the paper's alpha-synuclein and glial-activation conclusion while its explanation claimed replication of the junctional outcome; it now quotes the ZO-1 barrier integrity sentence, and the directional quote was kept as a separate item graded directness: INDIRECT. The node's description called it the 'gut-side terminus' of the brain-to-gut arm, which its own downstream edge contradicts, and now states that the arm joins the body-first chain at the shared barrier node. Also from the review: added cellular_components GO:0005923 bicellular tight junction alongside the process term, since the node makes a protein-abundance claim and GO:0120193 is a process; relaxed the edge into Intestinal Inflammation and Barrier Dysfunction from DIRECT to INDIRECT_KNOWN_INTERMEDIATES because that target bundles inflammation with barrier failure and only the barrier half is direct; and removed an unsourced 'near-complete' description of the rodent lesion extent. The review confirmed the four ontology bindings, all reference titles, every evidence_source, the omission of hypothesis groups, and that REFUTE is correct established usage here. PR #12545 review round (ai4c-reviewer, CHANGES_REQUESTED), and a correction to the record above. The review found that the rationale rewrite described in the previous paragraphs had been applied to the wrong discussion block. The edit script located the rationale with an unanchored string search over the whole file, which matched the first folded rationale scalar in the document rather than the intended one, so the corrected brain-to-gut text overwrote the rationale of the unrelated pd_pgc1a_therapeutic_window discussion, and the new pd_brain_to_gut_tight_junction_translation block kept the superseded first draft. The consequences were that an existing entry's argument was deleted from the repository, that the PGC-1alpha block's surviving decision_criterion referred to a rheostat and inverted-U framing no longer present anywhere, and that the new block's rationale contradicted its own fourth evidence item by offering levodopa masking as a candidate explanation while that item cited the levodopa-naive patients who rule it out. Fixed by restoring the pd_pgc1a_therapeutic_window rationale from origin/main, verified byte-identical, with its prompt, proposed_experiments and evidence also confirmed unchanged, and by moving the corrected brain-to-gut rationale into its own block, discarding the stale draft. The replacement was done with spans anchored on each discussion_id and asserted unique, rather than by whole-file search. The entry's diff against origin/main is now 303 insertions and zero deletions, which is the shape a purely additive curation should have; the 19 deletions the reviewer flagged were entirely this defect. Also taken from the review, as its optional suggestion: the body_first_enteric_alpha_synuclein_model notes already said dysbiosis was unresolved as trigger versus modifier or consequence, and now point at the new Striatal Dopamine Deficiency to Gut Microbiome Dysbiosis edge as the curated counterpart of the consequence reading, while restating why that edge is not tagged to the hypothesis group. Folded into the same push because every push drops the approval. The review independently confirmed all 14 snippets exact, all five ontology bindings with canonical labels including the biological_processes versus cellular_components split, every evidence_source, the four-way split of the human paper, the directness: INDIRECT grading on the second PMID:37271045 item, the withheld hypothesis group, the withheld conforms_to, and that the check-genereviews findings are pre-existing and correctly left alone.

Disorder ▸

Disorder

Name: Parkinson's Disease
Category: Complex
Existing deep-research providers: falcon
Existing evidence reference count in YAML: 67

Key Pathophysiology Nodes

Dopaminergic Neuron Loss
Alpha-Synuclein Aggregation
Mitochondrial Dysfunction
Neuroinflammation
Autophagy-Lysosome Pathway Dysfunction
Gut-Brain Axis Dysfunction
Oxidative Stress
Calcium Dysregulation
Endoplasmic Reticulum Stress
Synaptic Dysfunction
Iron Accumulation and Ferroptosis
Blood-Brain Barrier Dysfunction

Citation Inventory (for evidence mapping)

DOI:10.1016/s0140-6736(23
DOI:10.2147/ndt.s540718
DOI:10.3389/fnagi.2025.1617106
DOI:10.3390/cells14151161
DOI:10.3390/ijms25137183

Falcon ▸

Disease Pathophysiology Research Report

Edison Scientific Literature 15 citations 2025-12-17T18:36:16.429486

Disease Pathophysiology Research Report

Target Disease - Disease Name: Parkinson’s disease (PD) - MONDO ID: MONDO:0005180 - Category: Complex

1) Core Pathophysiology: current understanding - Alpha‑synuclein misfolding, aggregation, and propagation: PD pathogenesis centers on abnormal alpha‑synuclein (SNCA) aggregation into Lewy bodies/neurites with prion‑like spread across neural networks. Evidence integrates genetics (SNCA dosage/mutations), neuropathology (Lewy inclusions capturing mitochondria/lysosomes), and in vivo propagation models. As a recent authoritative review states: “abnormal alpha‑synuclein aggregation and spreading between gut, brainstem and higher brain regions [is] a likely substrate for disease initiation and progression,” with oligomers likely more toxic than large aggregates (The Lancet, Jan 2024; doi:10.1016/S0140-6736(23)01478-2) (morris2024thepathogenesisof pages 1-4). See also (morris2024thepathogenesisof pages 4-7, bai2025updatesonparkinson’s pages 7-8). - Mitochondrial dysfunction and mitophagy failure: Fundamental mitochondrial deficits (complex I impairment, ROS, ATP shortfall) occur early, interlinked with PINK1/Parkin mitophagy pathways; environmental complex I inhibitors (e.g., MPTP/pesticides) converge on this axis (Lancet 2024) (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4). - Lysosomal/autophagy and endo‑lysosomal trafficking defects: Genetics and pathway data implicate lysosomal pathways (e.g., GBA1, LRRK2, VPS35), with impaired proteostasis driving alpha‑syn accumulation (Lancet 2024; 2024 IJMS review) (morris2024thepathogenesisof pages 1-4, alvarez2024acomprehensiveapproach pages 2-4). - Neuroinflammation and glial crosstalk: Chronic microglial/astrocytic activation, cytokine cascades, and gut–brain immune signaling likely contribute to progression; immune‑inflammatory mechanisms are highlighted as key but incompletely resolved (Lancet 2024) (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4). - Calcium homeostasis, synaptic and axonal dysfunction: Early synaptic injury (vesicle trafficking, axonal transport) and calcium dysregulation precede neuronal loss, particularly in vulnerable nigrostriatal dopaminergic neurons (Lancet 2024) (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4). - Body‑first vs brain‑first and gut–brain axis: Both Braak’s peripheral‑to‑central model and a “brain‑first” trajectory are supported; prodromal autonomic/GI features and RBD support a body‑first subtype in a substantial subgroup (Lancet 2024; 2025 narrative synthesis) (morris2024thepathogenesisof pages 1-4, tanaka2025parkinson’sdiseasebridging pages 6-7, chaudhary2025understandingparkinson’sdisease pages 2-3).

2) Key Molecular Players - Genes/Proteins (HGNC): - SNCA (alpha‑synuclein): causal; mutations/dosage increase aggregation and drive aggressive phenotypes (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - LRRK2 (PARK8): most common Mendelian PD; kinase activity implicated; variants (e.g., G2019S, R1441) and downstream lysosomal/endolysosomal effects (Lancet 2024; IJMS 2024) (morris2024thepathogenesisof pages 1-4, alvarez2024acomprehensiveapproach pages 2-4). - PRKN (Parkin; PARK2), PINK1 (PARK6): recessive; central to mitophagy, mitochondrial quality control (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - PARK7 (DJ‑1): recessive; oxidative stress responses (IJMS 2024) (alvarez2024acomprehensiveapproach pages 2-4). - GBA1 (glucocerebrosidase): strongest risk factor among lysosomal enzyme genes; glucosylceramide handling, autophagy‑lysosomal pathways (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - VPS35: endosomal trafficking; links to lysosome/autophagy (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - Polygenic risk: “90 independent variants across 74 genomic loci” implicating lysosome–autophagy and immune pathways (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - Chemical entities (CHEBI) and modulators: - Dopamine (CHEBI:18243): neurotransmitter depleted in striatum; levodopa remains pivotal symptomatic therapy (IJMS 2024) (alvarez2024acomprehensiveapproach pages 2-4). - Glucosylceramide (CHEBI:18238): substrate in GBA1 pathway; links lipid metabolism to alpha‑syn burden (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - Alpha‑synuclein‑targeting biologics and small molecules: therapeutic development ongoing (NDT 2025) (bai2025updatesonparkinson’s pages 1-2). - LRRK2 kinase inhibitors: BBB‑penetrant candidates entering clinical testing (NDT 2025) (bai2025updatesonparkinson’s pages 1-2). - Cell types (CL): - Midbrain dopaminergic neuron, substantia nigra pars compacta (CL:0002609): selectively vulnerable (Lancet 2024) (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4). - Microglia (CL:0000129) and astrocytes (CL:0000127): drivers and modulators of neuroinflammation (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - Enteric neurons/glia (ENS): peripheral initiation sites in body‑first subtype (Lancet 2024) (morris2024thepathogenesisof pages 1-4). - Anatomical locations (UBERON): - Substantia nigra pars compacta (UBERON:0002038), striatum (UBERON:0002435): canonical motor circuit pathology (Lancet 2024) (morris2024thepathogenesisof pages 4-7). - Olfactory bulb (UBERON:0002312); dorsal motor nucleus of vagus (UBERON:0002826); enteric nervous system (UBERON:0007250): prodromal/peripheral staging nodes (Lancet 2024) (morris2024thepathogenesisof pages 1-4).

3) Biological Processes (GO) disrupted - Protein aggregation and amyloid fibril formation; synaptic vesicle cycle; axonal transport; calcium ion homeostasis (GO:0006816); oxidative phosphorylation and response to oxidative stress (GO:0006979); mitophagy (GO:0000423) and mitochondrial fission/fusion; autophagy (GO:0006914) and lysosomal organization; innate immune signaling and microglial activation. Mechanistic reviews emphasize mitochondria–ER–lysosome network disruption, with alpha‑syn propagating pathology across these systems (Lancet 2024; Cells 2025) (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4, tanaka2025parkinson’sdiseasebridging pages 6-7).

4) Cellular Components (GOCC) - Presynaptic terminals (alpha‑syn physiology/pathology), Lewy bodies/neurites (cytoplasmic inclusions capturing organelles), mitochondria, lysosomes, endosomes, ER, synaptic vesicles. Lewy bodies “trap organelles including mitochondria and lysosomes,” linking aggregation to organellar dysfunction (Lancet 2024, Jan 2024; doi link below) (morris2024thepathogenesisof pages 4-7).

5) Disease Progression and Staging - Sequence of events: prodrome → early synaptic/metabolic stress → alpha‑syn oligomer accumulation and fibril formation → organellar (mitochondria/lysosome) stress and impaired mitophagy → neuroinflammation/glial activation → progressive nigrostriatal degeneration and network spread → clinical motor syndrome and expanding non‑motor burden (Lancet 2024) (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4). - Braak staging and heterogeneity: classical six‑stage model proposes initial lesions in olfactory bulb/ENS with ascending spread; however, “many cases do not follow Braak staging,” and a brain‑first subtype also exists, underscoring divergent pathways (Lancet 2024) (morris2024thepathogenesisof pages 1-4). Body‑first vs brain‑first dichotomy and prodromal subtypes are emphasized in 2025 expert synthesis advocating biological definitions and prevention‑trial design (Cells 2025, Jul 2025; doi:10.3390/cells14151161) (tanaka2025parkinson’sdiseasebridging pages 6-7). - Prodromal markers: REM sleep behavior disorder (RBD), anosmia, constipation/autonomic dysfunction, subtle cognitive/affective changes are integrated into MDS criteria for prodromal PD (Lancet 2024) (morris2024thepathogenesisof pages 1-4).

6) Phenotypic Manifestations (HP terms) - Motor: bradykinesia (HP:0002067), rigidity (HP:0002063), resting tremor (HP:0002322), gait disturbance/postural instability (HP:0002066). These reflect nigrostriatal dopamine loss and basal ganglia circuit plasticity changes (Lancet 2024) (morris2024thepathogenesisof pages 4-7). - Non‑motor: hyposmia (HP:0004408), constipation (HP:0002019), orthostatic hypotension (HP:0001278), REM sleep behavior disorder (HP:0002362), depression/anxiety (HP:0000716/HP:0000739), cognitive impairment/dementia (HP:0100543/HP:0000726). These map to early involvement of olfactory, autonomic and limbic systems and widespread network pathology (Lancet 2024; Cells 2025) (morris2024thepathogenesisof pages 1-4, tanaka2025parkinson’sdiseasebridging pages 6-7).

7) Biomarkers and clinical tools (with URLs/dates) - Alpha‑synuclein seed amplification assays (SAA/RT‑QuIC): Biomarker panels now include α‑syn SAA from CSF or minimally invasive tissues; reviews highlight SAA’s high diagnostic performance in manifest/prodromal cohorts, while stressing standardization and access limitations. Notably, “alpha‑synuclein seed amplification assays…are being used clinically for biochemical diagnosis” in synucleinopathies, although broader deployment requires harmonization (published 2025/2024 syntheses) (NDT 2025, Sep 2025, https://doi.org/10.2147/ndt.s540718; Lancet 2024, Jan 2024, https://doi.org/10.1016/S0140-6736(23)01478-2) (bai2025updatesonparkinson’s pages 1-2, morris2024thepathogenesisof pages 1-4). A 2025 synthesis also emphasizes SAA utility within biomarker‑driven definitions and prevention trials (Cells 2025, Jul 2025, https://doi.org/10.3390/cells14151161) (tanaka2025parkinson’sdiseasebridging pages 6-7). - Imaging: Dopamine transporter (DAT) SPECT and advanced PET tracers delineate dopaminergic degeneration; neuromelanin and iron‑sensitive MRI support staging; multimodal imaging of inflammation and neurotransmitters is expanding for prodrome (Lancet 2024; NDT 2025) (https://doi.org/10.1016/S0140-6736(23)01478-2; https://doi.org/10.2147/ndt.s540718) (morris2024thepathogenesisof pages 1-4, bai2025updatesonparkinson’s pages 1-2). - Emerging alpha‑syn PET: First clinical alpha‑syn PET signals are reported in specific synucleinopathies and are anticipated to expand; timelines and challenges are discussed as part of a broader biomarker roadmap toward biological PD definitions (Cells 2025, Jul 2025) (tanaka2025parkinson’sdiseasebridging pages 6-7). - Digital biomarkers: Wearables and remote sensing aid motor/non‑motor phenotyping and may enrich trials; “digital phenotyping” can predict fluctuations and support early detection, though validation and equity are needed (NDT 2025, Sep 2025) (bai2025updatesonparkinson’s pages 1-2).

8) Current applications and real‑world implementations - Clinical practice: Combined use of clinical criteria (MDS), dopaminergic imaging when indicated, and selective application of fluid/tissue α‑syn SAA is growing in expert centers; expert reviews call for standardization and access expansion (Lancet 2024; NDT 2025) (morris2024thepathogenesisof pages 1-4, bai2025updatesonparkinson’s pages 1-2). - Trials and pipelines: Disease‑modifying strategies include α‑syn immunotherapies, lysosomal/mitophagy enhancers, and kinase modulators (e.g., LRRK2 inhibitors). Expert pipeline summaries highlight BBB‑penetrant LRRK2 inhibitors and α‑syn therapies progressing through phase II, with trial design evolving toward prodromal/biological staging (NDT 2025, Sep 2025; Cells 2025, Jul 2025) (bai2025updatesonparkinson’s pages 1-2, tanaka2025parkinson’sdiseasebridging pages 6-7). - Prevention framing: Given prodromal biomarkers (SAA, imaging, genetics), secondary prevention trials are advocated, with subtype‑specific enrichment (e.g., RBD cohorts, genetic carriers) (Cells 2025, Jul 2025) (tanaka2025parkinson’sdiseasebridging pages 6-7).

9) Expert opinions and analysis (authoritative sources, 2023–2025) - The Lancet 2024 review synthesizes genetics, organellar pathology, immune mechanisms, and heterogeneity, concluding: “There are currently no disease‑modifying treatments, but mechanistic insights… provide a basis for targeted neuroprotective strategies” (Jan 2024, https://doi.org/10.1016/S0140-6736(23)01478-2) (morris2024thepathogenesisof pages 1-4). - Recent expert syntheses emphasize a shift to biological definitions integrating α‑syn SAA/imaging, genetics, and digital phenotyping, and call for prevention‑trial designs and equitable biomarker access (Cells 2025, Jul 2025, https://doi.org/10.3390/cells14151161; NDT 2025, Sep 2025, https://doi.org/10.2147/ndt.s540718) (tanaka2025parkinson’sdiseasebridging pages 6-7, bai2025updatesonparkinson’s pages 1-2).

10) Relevant statistics and recent epidemiology (2019–2024) - Global burden: PD affects “over ten million individuals” worldwide, with rising prevalence over the last decade and incidence typically 8–18 per 100,000 person‑years; male predominance ~1.5×; early‑onset PD 5–10% (NDT 2025, Sep 2025, https://doi.org/10.2147/ndt.s540718) (bai2025updatesonparkinson’s pages 1-2). Contemporary global analyses cited by these reviews corroborate increasing age‑standardized prevalence and regional heterogeneity (Lancet 2024, Jan 2024, https://doi.org/10.1016/S0140-6736(23)01478-2) (morris2024thepathogenesisof pages 1-4).

Structured Annotations for a Knowledge Base - Pathophysiology (summary): Aggregated α‑synuclein seeds propagate across neural/peripheral networks, impairing synapses and organellar homeostasis (mitochondria–lysosome–ER). Mitophagy failure (PINK1/PRKN) and lysosomal dysfunction (GBA1, LRRK2, VPS35) amplify proteostasis stress and neuroinflammation, culminating in nigrostriatal degeneration and widespread network involvement (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4). - Gene/Protein annotations (HGNC): SNCA; LRRK2; PRKN; PINK1; PARK7; GBA; VPS35 (morris2024thepathogenesisof pages 1-4, alvarez2024acomprehensiveapproach pages 2-4). - GO Biological Processes: mitophagy (GO:0000423); autophagy (GO:0006914); synaptic vesicle cycle (GO:0099504); axonal transport (GO:0098930); calcium ion homeostasis (GO:0006874); response to oxidative stress (GO:0006979); innate immune response (GO:0045087) (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4). - GO Cellular Components: presynapse (GO:0098793); mitochondrion (GO:0005739); lysosome (GO:0005764); endosome (GO:0005768); Lewy body (GO:0097418) (morris2024thepathogenesisof pages 4-7). - Cell Types (CL): dopaminergic neuron, SNpc (CL:0002609); microglial cell (CL:0000129); astrocyte (CL:0000127); enteric neuron (CL:0000700) (morris2024thepathogenesisof pages 1-4). - Anatomy (UBERON): substantia nigra pars compacta (UBERON:0002038); striatum (UBERON:0002435); olfactory bulb (UBERON:0002312); dorsal motor nucleus of vagus (UBERON:0002826); enteric nervous system (UBERON:0007250) (morris2024thepathogenesisof pages 1-4). - Chemical Entities (CHEBI): dopamine (CHEBI:18243); glucosylceramide (CHEBI:18238); representative therapeutic classes: LRRK2 kinase inhibitors; α‑synuclein immunotherapies (bai2025updatesonparkinson’s pages 1-2, morris2024thepathogenesisof pages 1-4).

Direct supporting statements (quotes) - “Abnormal alpha‑synuclein aggregation and spreading between gut, brainstem and higher brain regions [is] a likely substrate for disease initiation and progression.” (The Lancet, Jan 2024, https://doi.org/10.1016/S0140-6736(23)01478-2) (morris2024thepathogenesisof pages 1-4) - “Cellular mechanisms implicated across monogenic and sporadic PD include mitochondrial, lysosomal and endosomal dysfunction, and maladaptive immune/inflammatory responses.” (The Lancet, Jan 2024, ibid.) (morris2024thepathogenesisof pages 1-4) - “There are currently no disease‑modifying treatments, but mechanistic insights… provide a basis for targeted neuroprotective strategies.” (The Lancet, Jan 2024, ibid.) (morris2024thepathogenesisof pages 1-4) - Reviews from 2025 emphasize a biomarker‑based, prevention‑trial framework: “biological definition… integrating in vivo detection of neuronal α‑synuclein aggregation, neurodegeneration and genetics” (Cells, Jul 2025, https://doi.org/10.3390/cells14151161) (tanaka2025parkinson’sdiseasebridging pages 6-7).

Notes on scope and limitations - GLP‑1 receptor agonists and other metabolic approaches are active areas, but detailed clinical meta‑analyses were not directly quoted in the evidence items here; we therefore limited claims to pipeline‑level commentary in authoritative reviews (bai2025updatesonparkinson’s pages 1-2). For detailed efficacy estimates, consult recent trial/meta‑analytic papers.

References (with links and dates) - Morris HR, Spillantini MG, Sue CM, Williams‑Gray CH. The pathogenesis of Parkinson’s disease. The Lancet. 2024 Jan;403:293–304. doi:10.1016/S0140-6736(23)01478-2. https://doi.org/10.1016/S0140-6736(23)01478-2 (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4) - Bai H, Ma W, Zhu L, et al. Updates on Parkinson’s Disease. Neuropsychiatric Disease and Treatment. 2025 Sep;21:1945–1953. doi:10.2147/ndt.s540718. https://doi.org/10.2147/ndt.s540718 (bai2025updatesonparkinson’s pages 1-2, bai2025updatesonparkinson’s pages 7-8) - Tanaka M. Parkinson’s Disease: Bridging Gaps, Building Biomarkers, and Reimagining Clinical Translation. Cells. 2025 Jul;14:1161. doi:10.3390/cells14151161. https://doi.org/10.3390/cells14151161 (tanaka2025parkinson’sdiseasebridging pages 6-7, tanaka2025parkinson’sdiseasebridging pages 2-4) - Álvarez MM, Cano‑Herrera G, Osorio Martínez MF, et al. A Comprehensive Approach to Parkinson’s Disease: Addressing Its Molecular, Clinical, and Therapeutic Aspects. International Journal of Molecular Sciences. 2024 Jun;25:7183. doi:10.3390/ijms25137183. https://doi.org/10.3390/ijms25137183 (alvarez2024acomprehensiveapproach pages 2-4)

Overall synthesis: Contemporary consensus places alpha‑synuclein aggregation/propagation at the core of PD, intersecting with mitochondrial and lysosomal/autophagy dysfunction and immune signaling to produce early synaptic failure and progressive network neurodegeneration. Heterogeneous trajectories (brain‑first, body‑first) map to prodromal markers and likely subtypes. Biomarker advances—especially α‑syn SAA, dopaminergic imaging, and emerging α‑syn PET—support a shift toward biologically defined diagnosis and prevention‑trial designs, while pipelines target α‑syn, LRRK2, lysosome and mitophagy for disease modification. The global burden continues to rise with aging populations, underscoring the urgency of biomarker‑driven, mechanistically informed interventions (morris2024thepathogenesisof pages 4-7, morris2024thepathogenesisof pages 1-4, bai2025updatesonparkinson’s pages 1-2).

References

(morris2024thepathogenesisof pages 1-4): Huw R Morris, Maria Grazia Spillantini, Carolyn M Sue, and Caroline H Williams-Gray. The pathogenesis of parkinson's disease. The Lancet, 403:293-304, Jan 2024. URL: https://doi.org/10.1016/s0140-6736(23)01478-2, doi:10.1016/s0140-6736(23)01478-2. This article has 739 citations and is from a highest quality peer-reviewed journal.
(morris2024thepathogenesisof pages 4-7): Huw R Morris, Maria Grazia Spillantini, Carolyn M Sue, and Caroline H Williams-Gray. The pathogenesis of parkinson's disease. The Lancet, 403:293-304, Jan 2024. URL: https://doi.org/10.1016/s0140-6736(23)01478-2, doi:10.1016/s0140-6736(23)01478-2. This article has 739 citations and is from a highest quality peer-reviewed journal.
(bai2025updatesonparkinson’s pages 7-8): Hong Bai, Wenhui Ma, Lei Zhu, Yaling Lu, Jiaojiao Fan, Mengjia Chen, and Cong Huang. Updates on parkinson’s disease. Neuropsychiatric Disease and Treatment, Volume 21:1945-1953, Sep 2025. URL: https://doi.org/10.2147/ndt.s540718, doi:10.2147/ndt.s540718. This article has 1 citations and is from a peer-reviewed journal.
(alvarez2024acomprehensiveapproach pages 2-4): Mauricio Muleiro Alvarez, Gabriela Cano-Herrera, María Fernanda Osorio Martínez, Joaquin Vega Gonzales-Portillo, Germán Rivera Monroy, Renata Murguiondo Pérez, Jorge Alejandro Torres-Ríos, Ximena A. van Tienhoven, Ernesto Marcelo Garibaldi Bernot, Felipe Esparza Salazar, and Antonio Ibarra. A comprehensive approach to parkinson’s disease: addressing its molecular, clinical, and therapeutic aspects. International Journal of Molecular Sciences, 25:7183, Jun 2024. URL: https://doi.org/10.3390/ijms25137183, doi:10.3390/ijms25137183. This article has 51 citations and is from a poor quality or predatory journal.
(tanaka2025parkinson’sdiseasebridging pages 6-7): Masaru Tanaka. Parkinson’s disease: bridging gaps, building biomarkers, and reimagining clinical translation. Cells, 14:1161, Jul 2025. URL: https://doi.org/10.3390/cells14151161, doi:10.3390/cells14151161. This article has 16 citations and is from a poor quality or predatory journal.
(chaudhary2025understandingparkinson’sdisease pages 2-3): Sameer A. Chaudhary, Sapana Chaudhary, and Sakshi Rawat. Understanding parkinson’s disease: current trends and its multifaceted complications. Frontiers in Aging Neuroscience, Sep 2025. URL: https://doi.org/10.3389/fnagi.2025.1617106, doi:10.3389/fnagi.2025.1617106. This article has 1 citations and is from a peer-reviewed journal.
(bai2025updatesonparkinson’s pages 1-2): Hong Bai, Wenhui Ma, Lei Zhu, Yaling Lu, Jiaojiao Fan, Mengjia Chen, and Cong Huang. Updates on parkinson’s disease. Neuropsychiatric Disease and Treatment, Volume 21:1945-1953, Sep 2025. URL: https://doi.org/10.2147/ndt.s540718, doi:10.2147/ndt.s540718. This article has 1 citations and is from a peer-reviewed journal.
(tanaka2025parkinson’sdiseasebridging pages 2-4): Masaru Tanaka. Parkinson’s disease: bridging gaps, building biomarkers, and reimagining clinical translation. Cells, 14:1161, Jul 2025. URL: https://doi.org/10.3390/cells14151161, doi:10.3390/cells14151161. This article has 16 citations and is from a poor quality or predatory journal.

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Parkinson's Disease: Comprehensive Disease Characteristics Report

openscientist-autonomous 50 citations 2026-09-22T22:27:58.975237

Parkinson's Disease: Comprehensive Disease Characteristics Report

Disease: Parkinson's Disease · MONDO: MONDO:0005180 · Category: Complex (multifactorial neurodegenerative) Report type: Knowledge-base entry synthesized from 5 autonomous research iterations (9 confirmed findings, 65 papers reviewed)

Summary

Parkinson's disease (PD) is a chronic, progressive, multifactorial neurodegenerative movement disorder — the second most common neurodegenerative disease after Alzheimer's disease. It is defined pathologically by the selective loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and by intraneuronal α-synuclein aggregates (Lewy bodies and Lewy neurites). Nigrostriatal degeneration depletes striatal dopamine, disrupting basal-ganglia motor circuitry and producing the cardinal motor syndrome of bradykinesia, rigidity, and resting tremor, accompanied by a broad and often prodromal non-motor spectrum (hyposmia, REM-sleep behavior disorder, constipation, autonomic and neuropsychiatric features).

Etiologically, PD sits at the intersection of aging (the dominant risk factor), genetics, and environment. Roughly 5–10% of cases are monogenic, caused by highly penetrant mutations in autosomal-dominant genes (SNCA, LRRK2, VPS35) and autosomal-recessive, early-onset genes (PRKN/Parkin, PINK1, PARK7/DJ-1). The strongest common genetic risk factors are incomplete-penetrance variants in GBA1 and LRRK2 (e.g., G2019S), and genome-wide association studies have identified >90 risk loci of small effect that shape sporadic disease. Environmental risk (pesticides, dairy, head trauma) and protective factors (smoking, caffeine, physical activity) interact with genotype — most strikingly, occupational pesticide exposure sharply amplifies PD odds in GBA1 carriers (adjusted OR 5.4). Mechanistically, the monogenic genes converge on impaired mitochondrial quality control (PINK1/Parkin mitophagy) and lysosomal/autophagic clearance, feeding a self-reinforcing cascade of α-synuclein misfolding and prion-like spread, oxidative stress, and neuroinflammation.

Clinically, diagnosis remains primarily clinical (MDS-2015 criteria) but is now strongly supported by two molecular/imaging tools: dopamine-transporter (DaT) imaging and the α-synuclein seed amplification assay (SAA/RT-QuIC), which detects misfolded α-synuclein seeds with ~93–95% sensitivity and specificity and turns positive years before motor onset in prodromal cohorts. Treatment is symptomatic and effective for years — levodopa, dopamine agonists, MAO-B/COMT inhibitors, and device-aided therapies (deep brain stimulation, infusion pumps, focused ultrasound) — but no disease-modifying therapy is approved. The leading anti-α-synuclein monoclonal antibodies (prasinezumab, cinpanemab) failed their Phase II primary endpoints, underscoring gaps between target engagement and clinical benefit and motivating earlier intervention, better biomarkers, and mechanistically broader (intracellular, metabolic) strategies.

Key Findings

F001 — Core neuropathology: nigrostriatal dopaminergic degeneration plus α-synuclein Lewy bodies

The defining lesion of PD is the progressive degeneration of dopaminergic neurons predominantly in the substantia nigra pars compacta, which reduces dopaminergic input to the striatum and depletes striatal dopamine. This dopamine deficit disrupts the direct/indirect basal-ganglia motor loops and produces the cardinal motor features — bradykinesia, rigidity, and resting tremor. The neuropathological hallmark is the intraneuronal Lewy body, an inclusion composed mainly of aggregated α-synuclein (SNCA protein product). As one review states, "Central to its pathophysiology is the degeneration of dopaminergic neurons in the substantia nigra, leading to a significant decrease in striatal dopamine (DA) levels" (PMID: 41904982), and another confirms "The neuropathology hallmark of PD is the loss of dopaminergic neurons predominantly in the substantia nigra pars compacta and the presence of intracellular inclusions termed Lewy bodies (LBs), which are mainly composed of α-synuclein (αSyn)" (PMID: 35362115). Additional post-mortem work links SNpc dopaminergic loss to neuromelanin depletion and oxidative-stress markers (e.g., loss of TXNIP–neuromelanin association in late-stage PD; PMID: 40868900).

Ontology anchors: UBERON:0001965 (substantia nigra pars compacta), UBERON:0002435 (striatum), CL:0000700 (dopaminergic neuron), GO:0005739 (mitochondrion); CHEBI:18243 (dopamine); HP:0002067 (bradykinesia), HP:0002063 (rigidity), HP:0002322 (resting tremor).

F002 — Genetic architecture: monogenic genes plus incomplete-penetrance risk variants

PD genetics span a spectrum from rare high-penetrance Mendelian forms to common low-effect risk alleles. Highly penetrant mutations cause monogenic PD in ~5–10% of cases: autosomal-dominant SNCA, LRRK2, and VPS35, and autosomal-recessive, typically early-onset PRKN/Parkin, PINK1, and DJ-1/PARK7. Incomplete-penetrance variants in LRRK2 (e.g., p.G2019S) and GBA1 are the strongest common genetic risk factors, and GWAS have identified >90 loci that each contribute small increments to sporadic disease. A foundational review summarizes: "Highly-penetrant mutations in different genes (SNCA, LRRK2, VPS35, Parkin, PINK1, and DJ-1) are known to cause rare monogenic forms of the disease. Furthermore, different variants with incomplete penetrance in the LRRK2 and the GBA gene are strong risk factors for PD" (PMID: 24262182). Complementary work extends the list of loci (ATP13A2, FBXO7, PLA2G6, EIF4G1) and confirms that Mendelian-gene polymorphisms also modestly influence "sporadic" risk (PMID: 22806825; PMID: 22166458).

HGNC/gene anchors: SNCA (HGNC:11138, OMIM 163890; PD OMIM 168601/605543), LRRK2 (HGNC:18618, OMIM 609007; PARK8 607060), VPS35 (HGNC:13487; PARK17 614203), PRKN/PARK2 (HGNC:8607; PARK2 600116), PINK1 (HGNC:14581; PARK6 605909), PARK7/DJ-1 (HGNC:16369; PARK7 606324), GBA1 (HGNC:4177; OMIM 606463).

F003 — Gene–environment interaction: pesticide exposure sharply raises PD odds in GBA1 carriers

Genetic and environmental risks are not independent. In the Parkinson's Progression Markers Initiative (PPMI), GBA-variant carriers with occupational pesticide exposure had markedly elevated PD odds (adjusted OR 5.4, 95% CI 1.7–18.5, p<0.01), whereas LRRK2-G2019S carriers showed only a non-significant elevation (aOR 1.3, 95% CI 0.4–4.6): "People with a GBA variant and occupational pesticide exposure had much higher odds of PD (aOR: 5.4, 95% CI 1.7–18.5, p < 0.01)" (PMID: 38820021). At the population level, the modifiable-risk-factor landscape is well characterized: "Physical activity, healthy dietary patterns, smoking, and caffeine intake are protective factors against PD. Head trauma, consumption of milk and dairy products, and pesticide exposure were associated with a higher risk of developing PD" (PMID: 40107260). Prospective cohorts reinforce that only a handful of factors have both epidemiologic strength and biological plausibility — risk: pesticides, dairy, β2-adrenoceptor antagonists; protective: smoking, caffeine/tea, physical activity, uric acid/gout, NSAIDs, vitamin E, β2-agonists (PMID: 31706021; PMID: 28189372; PMID: 23055790).

CHEBI anchors: CHEBI:34905 (paraquat), CHEBI:8148 (rotenone), CHEBI:27958 (nicotine/tobacco), CHEBI:27732 (caffeine).

F004 — Monogenic genes converge on impaired mitophagy / mitochondrial quality control

A central unifying mechanism is defective mitochondrial quality control. The kinase PINK1 and the E3 ubiquitin ligase PRKN/Parkin cooperate to amplify ubiquitin signals on damaged mitochondria, driving their selective autophagic removal (mitophagy); recessive loss-of-function mutations cause early-onset PD: "A kinase PINK1 and an E3 ubiquitin ligase PRKN/Parkin, both of which are mutated in familial Parkinson disease, amplify ubiquitin signals on the damaged mitochondria" (PMID: 42681746). Autosomal-dominant genes feed into the same pathway: LRRK2 mutations disrupt PINK1/Parkin mitophagy, and the VPS35 p.D620N mutation acts through increased LRRK2 kinase activity (a gain-of-function that impairs mitochondrial Parkin recruitment): "PINK1/parkin-mediated mitophagy is disrupted by LRRK2 mutations, which are the most prevalent cause of autosomal dominant Parkinson's disease" (PMID: 41164908). Downstream effectors include the autophagy receptor OPTN and an OPTN–RAB1–ATG9A axis (PMID: 42681746). This convergence explains how genetically distinct forms of PD share a common cellular pathology.

GO anchors: GO:0000422 (mitophagy), GO:0006914 (autophagy), GO:0006511 (ubiquitin-dependent protein catabolic process), GO:0005739 (mitochondrion), GO:0005764 (lysosome).

F005 — α-synuclein seed amplification assay (SAA/RT-QuIC) is a high-accuracy molecular diagnostic

Seed amplification assays have transformed PD diagnostics. CSF real-time quaking-induced conversion (RT-QuIC) detects misfolded α-synuclein seeds with sensitivity 93.3–94.6% and pooled specificity 94% (95% CI 0.92–0.96) for sporadic PD/DLB: "Cerebrospinal fluid (CSF)-based real-time quaking-induced conversion (RT-QuIC) demonstrates exceptional diagnostic accuracy for sporadic Parkinson's disease (PD) and dementia with Lewy bodies (DLB), with sensitivity reaching 93.3%-94.6% and pooled specificity of 94% (95% CI: 0.92-0.96)" (PMID: 42141805). A network meta-analysis independently ranks CSF α-syn SAA highest (sensitivity 0.91, specificity 0.95 vs controls; PMID: 41324773). Skin and intestinal-tissue assays reach up to ~94% accuracy, and in idiopathic REM-sleep behavior disorder (prodromal) cohorts positivity exceeds 80%, detecting pathology years before diagnosis. Assay strain typing can distinguish PD/DLB from MSA. Caveats: inter-laboratory/protocol variability remains substantial (DLB cross-lab sensitivity 55–100%; PMID: 41604609; PMID: 42201636), so harmonization is needed before universal clinical adoption.

F006 — No disease-modifying therapy exists; α-synuclein antibodies failed Phase II

All approved PD therapies are symptomatic (dopaminergic replacement, deep brain stimulation); none halts neurodegeneration. The two leading anti-α-synuclein monoclonal antibodies — prasinezumab (PASADENA) and cinpanemab (SPARK) — were generally safe but failed primary efficacy endpoints: "recent Phase II clinical trials, including PASADENA and SPARK, failed to achieve their primary clinical endpoints, highlighting a substantial gap between biological target engagement and meaningful clinical benefit" (PMID: 42227981). Specific non-significant p-values were reported: "Phase-II trials failed to meet their primary efficacy endpoints and showed no significant slowing of disease progression (Cinpanemab 250 mg P-value = 0.7, 1250 mg P-value = 0.78, 3500 mg P-value = 0.7; Prasinezumab 1500 mg P-value = 0.24, 4500 mg P-value = 0.72)" (PMID: 41702332). A systematic review concurs that cinpanemab showed almost no efficacy while prasinezumab's mixed signals weakened after excluding high-risk-of-bias studies (PMID: 42495570). Proposed reasons include late intervention timing, poor blood–brain-barrier penetration (CSF:serum ~0.2–0.5%), pathology heterogeneity, insensitive outcome measures (MDS-UPDRS), and possible over-emphasis on extracellular prion-like spread relative to intracellular metabolic autotoxicity (aminochrome, mitochondrial dysfunction, oxidative stress — the "Single-Neuron Degeneration Hypothesis"; PMID: 42459575).

F007 — Neuroinflammation and adaptive immunity contribute to dopaminergic neurodegeneration

PD is not a cell-autonomous disease alone; immune mechanisms amplify neuronal loss. Extracellular α-synuclein aggregates act as damage-associated molecular patterns (DAMPs), and autoantibodies against α-synuclein appear in PD CSF and serum: "Extracellular α-syn aggregates act as a damage-associated molecular pattern (DAMP) and the presence of autoantibodies against α-syn species in the cerebrospinal fluid and the serum of PD patients implicate the involvement of innate and adaptive immune responses" (PMID: 31796095). α-synuclein-specific T-cell responses drive neurotoxicity: "The immunization of mice with α-Syn peptides resulted in enhanced autoimmune responses, such as the peptide recall response, polarization toward Th1/Th17 cells, and regulatory T cell imbalance" (PMID: 38788538). Microglial activation, neurotoxic A1 astrocytes, and infiltrating B, CD4+/CD8+ T, and NK cells accompany α-synuclein inclusions in preformed-fibril mouse models. Blood–brain-barrier breakdown forms a vicious cycle with neuroinflammation and α-synuclein deposition (PMID: 41735220), and cellular senescence with a pro-inflammatory secretory phenotype adds an aging-linked inflammatory driver (PMID: 41806646).

GO/CL anchors: GO:0006954 (inflammatory response), GO:0002250 (adaptive immune response); CL:0000129 (microglial cell), CL:0000127 (astrocyte), CL:0000624 (CD4+ T cell), CL:0000625 (CD8+ T cell).

F008 — Prion-like gut-to-brain α-synuclein propagation underlies caudorostral Braak staging

α-synuclein pathology spreads cell-to-cell in a prion-like manner. In the "body-first" subtype, gut Lewy pathology propagates via the vagus nerve to the brainstem/pons, then substantia nigra, then diencephalon and cortex — matching the caudorostral Braak staging scheme: "α-synuclein aggregates originating from the gut transmit to the brain through the vagus nerve, employing a prion-like mechanism that promotes Lewy body pathology" (PMID: 41052745). Colonic phosphorylated α-synuclein histopathology increases in parallel with Braak/Arizona stage and correlates with sleep/wake dysfunction and RBD: "Colonic PASH frequency also increased in parallel to presumed PD Braak and Arizona stage classifications" (PMID: 37873268). Clinically, prodromal symptoms tracking a shared body-first origin cluster together (e.g., RBD closely associated with constipation in de novo PD; PMID: 36098886).

UBERON/GO anchors: UBERON:0001759 (vagus nerve), UBERON:0001155 (colon), UBERON:0000988 (pons).

F009 — GBA1-PD: age-dependent penetrance and a more aggressive phenotype

GBA1 variants are the most common genetic risk factor for PD, yet penetrance is low and age-dependent — most carriers never develop synucleinopathy. In biallelic Gaucher disease type 1, age-specific PD prevalence rose from 4.0% (95% CI 2.7–5.7) at 60 years to 12.2% (8.6–17.0) at 80 years (~1 in 9; ~1 in 5 including parkinsonian signs): "The age-specific prevalence (95% CI) of PD and pPS was 4.0% (2.7-5.7) and 6.0% (4.5-7.9) at 60 years and 12.2% (8.6-17.0) and 22.9% (17.1-30.1) at 80 years, respectively" (PMID: 42085646). When PD does develop, GBA1-PD is more aggressive: "The clinical profile of GBA1-associated Parkinson's disease is characterised by a faster rate of progression with more severe cognitive and autonomic dysfunction than idiopathic Parkinson's disease, particularly in those carrying severe pathogenic variants" (PMID: 42127935). Variant severity stratifies risk: severe (L444P/L483P), mild (N370S/N409S), and risk-only (E326K/E365K, T369M/T408M) alleles, with ethnicity-specific distributions and earlier onset in Asian carriers (PMID: 39927608).

Detailed Section Report

1. Disease Information

PD is a chronic, progressive neurodegenerative movement disorder, the second most common neurodegenerative disease. Identifiers: MONDO:0005180; OMIM 168600 (susceptibility) with monogenic loci PARK1-PARK23; Orphanet ORPHA:2828; ICD-10 G20; ICD-11 8A00.0; MeSH D010300 (Parkinson Disease); DOID:14330. Synonyms: idiopathic Parkinson's disease, primary parkinsonism, paralysis agitans, Lewy body Parkinson's disease. Information here derives from aggregated disease-level resources (OMIM, Orphanet, systematic reviews, GWAS meta-analyses, registries such as PPMI and the ICGG Gaucher Registry) rather than individual EHR records.

2. Etiology

Causal factors: multifactorial — aging (dominant), genetics, and environment. Genetic risk: monogenic SNCA/LRRK2/VPS35 (AD), PRKN/PINK1/PARK7 (AR early-onset); strong common risk from GBA1 and LRRK2 incomplete-penetrance variants; >90 GWAS loci (F002). Environmental risk: pesticides/herbicides (paraquat, rotenone, maneb), heavy metals (manganese, lead), head trauma, dairy consumption, well-water/rural living (F003; PMID: 28189372). Protective factors: cigarette smoking, caffeine/tea, physical activity, higher serum urate/gout, NSAID use, vitamin E; no well-established protective genetic variant is confirmed here. Gene–environment interaction: GBA1 × pesticide OR 5.4 (F003) is the strongest documented GxE effect; environment-genetic interplay is proposed to contribute more than either alone (PMID: 23055790).

3. Phenotypes

Motor (cardinal): bradykinesia (HP:0002067), rigidity (HP:0002063), resting tremor (HP:0002322), postural instability/gait impairment (HP:0002172), typically asymmetric at onset, adult/late-onset, progressive. Non-motor / prodromal: hyposmia (HP:0000458), REM-sleep behavior disorder, constipation (HP:0002019), depression (HP:0000716), anxiety, orthostatic hypotension/autonomic dysfunction (HP:0001278), cognitive impairment/dementia (HP:0000726), psychosis and impulse-control disorders (often treatment-related). Prodromal markers precede motor onset by 5 to >20 years, with the strongest predictive value for RBD, hyposmia, and constipation (PMID: 27786242; PMID: 35180132). QoL impact: PD substantially reduces health-related quality of life and independence, driving high direct/indirect and informal-care costs (mean €14,278/patient/year in Europe; PMID: 42659761).

4. Genetic / Molecular Information

Causal genes: SNCA, LRRK2, VPS35 (AD); PRKN, PINK1, PARK7/DJ-1, ATP13A2, FBXO7, PLA2G6 (AR). Variant examples: SNCA A53T, duplications/triplications (gain-of-function/dosage); LRRK2 p.G2019S (kinase gain-of-function, the most common single mutation); VPS35 p.D620N; GBA1 N370S/N409S (mild), L444P/L483P (severe), E326K/T369M (risk). Classification: per ACMG/AMP, LRRK2 G2019S and severe GBA1 alleles are pathogenic/likely pathogenic; E326K/T369M are risk factors of uncertain individual pathogenicity. Allele frequency: GBA1 and LRRK2 risk-variant frequencies vary by ancestry (e.g., LRRK2 G2019S enriched in Ashkenazi Jewish and North African Berber populations; PMID: 41735653). Origin: germline. Functional consequences: SNCA — toxic gain-of-function aggregation; LRRK2 — kinase gain-of-function; PRKN/PINK1/DJ-1 — loss-of-function; VPS35 — gain-of-function via LRRK2. Modifier genes: GBA1 modifies progression/cognition; ancestry modifies LRRK2 penetrance. Epigenetics/chromosomal: SNCA promoter methylation changes reported; large-scale chromosomal abnormalities are not a defining feature.

5. Environmental Information

Toxins: pesticides/herbicides (paraquat, rotenone, maneb), metals (Mn, Pb), solvents; MPTP is a well-known dopaminergic toxin used experimentally. Lifestyle: smoking, caffeine, and physical activity lower risk; dairy raises risk; alcohol equivocal. Infectious agents: no established causative pathogen; PD is not an infectious disease, though the gut microbiome and inflammation are implicated in modulating pathology (F008). Air pollution and rural/agricultural exposure are epidemiologically associated (PMID: 20187243).

6. Mechanism / Pathophysiology — Ordered Causal Chain

1. INITIATING LESION (branch A: genetic — SNCA/LRRK2/VPS35/PRKN/PINK1/DJ-1/GBA1 variants;
   branch B: environmental — pesticide/toxin exposure, aging; often A×B interaction, e.g. GBA1×pesticide OR 5.4)
│  leads to
▼
2. Impaired mitochondrial quality control (PINK1/Parkin mitophagy failure; LRRK2 & VPS35 D620N
   converge here) AND impaired lysosomal/autophagic clearance (GBA1 → glucocerebrosidase deficiency)
│  results in
▼
3. Accumulation and misfolding of α-synuclein → oligomers and fibrils (aided by oxidative stress,
   dopamine-derived aminochrome, reduced clearance)
│  leads to
▼
4. Formation of intraneuronal Lewy bodies/neurites; α-synuclein acts as a DAMP
│  branches:
├─(4a) Prion-like cell-to-cell spread — gut → vagus nerve → brainstem → SNpc → cortex
│       (caudorostral Braak staging; "body-first" subtype)   [inferred from model + tissue data]
└─(4b) Neuroinflammation — microglial activation, A1 astrocytes, α-syn-specific Th1/Th17 T cells,
        BBB breakdown, cellular senescence (SASP)
│  together result in
▼
5. Selective degeneration of SNpc dopaminergic neurons (oxidative stress, mitochondrial failure,
   iron/neuromelanin dysregulation) — upstream lesion; white-matter/oligodendrocyte involvement may precede
│  leads to
▼
6. Striatal dopamine depletion → basal-ganglia circuit dysfunction (direct/indirect pathway imbalance)
│  results in
▼
7. CLINICAL MANIFESTATION: cardinal motor syndrome (bradykinesia, rigidity, resting tremor,
   postural instability) + non-motor/prodromal features (hyposmia, RBD, constipation, autonomic,
   cognitive, neuropsychiatric)

Upstream vs downstream: Steps 1–3 (genetic/toxic triggers, mitophagy/lysosomal failure, α-synuclein misfolding) are upstream; steps 5–7 (dopaminergic death, dopamine depletion, motor signs) are downstream. Neuroinflammation (4b) and prion-like spread (4a) are amplifying loops that are both consequence and cause. Molecular pathways: ubiquitin–proteasome/autophagy–lysosome, PINK1/Parkin mitophagy, LRRK2 kinase signaling, glucocerebrosidase/sphingolipid metabolism, oxidative-stress/NRF2 axis. Cell types: dopaminergic neurons (CL:0000700), microglia (CL:0000129), astrocytes (CL:0000127), oligodendrocyte precursors (PMID: 42397532). Subcellular compartments: mitochondria (GO:0005739), lysosome (GO:0005764), presynaptic terminal.

7. Anatomical Structures Affected

Primary organ: brain — substantia nigra pars compacta (UBERON:0001965) and nigrostriatal pathway/striatum (UBERON:0002435). Body system: central and autonomic nervous system. Spread pattern: dorsal motor nucleus of vagus/olfactory bulb → pons/locus coeruleus → SNpc → limbic → neocortex (Braak). Secondary involvement: enteric nervous system/colon (UBERON:0001155), heart (cardiac sympathetic denervation), olfactory bulb, white-matter tracts. Cell populations: SNpc dopaminergic (neuromelanin-containing) neurons, plus cholinergic, noradrenergic (locus coeruleus), and serotonergic populations. Subcellular: mitochondria, lysosomes, presynapse. Lateralization: characteristically asymmetric/unilateral at onset, becoming bilateral with progression.

8. Temporal Development

Onset: typically adult/late-onset (mean ~60 years); early-onset (<50) and juvenile forms occur, often monogenic (PRKN, PINK1). Onset pattern: insidious and chronic, preceded by a prodromal phase lasting 5 to >20 years. Stages: prodromal → early clinical (Hoehn & Yahr I–II) → intermediate (III) → advanced (IV–V) with motor fluctuations, dyskinesia, falls, dementia. Progression: slow but relentless and variable; GBA1 and older age at onset predict faster decline and dementia (PMID: 42127935; PMID: 41944089). Course: progressive, lifelong, chronic; no spontaneous remission. Critical window: the prodromal/early stage is the presumed opportunity for disease-modifying intervention (F006).

9. Inheritance and Population

Epidemiology: one of the fastest-growing neurological disorders; prevalence rises steeply with age (global burden growing, largely from aging/population growth rather than rising age-specific incidence; PMID: 42689419). Inheritance: predominantly multifactorial/polygenic; monogenic subsets are AD (SNCA, LRRK2, VPS35) or AR (PRKN, PINK1, DJ-1). Penetrance: incomplete and age-dependent (GBA1 ~4%→12% by age 60→80 in Gaucher type 1; LRRK2 G2019S variable by ancestry). Expressivity: variable. Founder effects: LRRK2 G2019S in Ashkenazi Jewish and North African Berber populations; GBA1 N370S in Ashkenazi Jews. Sex ratio: male predominance (~1.4–1.5:1). Geographic/ancestry variation: earlier onset in Asian GBA1/LRRK2 carriers; rising incidence in regions such as the UAE (PMID: 42656222).

10. Diagnostics

Clinical criteria: MDS-2015 clinical diagnostic criteria (parkinsonism = bradykinesia + rest tremor and/or rigidity; supportive/exclusion/red-flag features). Imaging: dopamine-transporter (DaT) SPECT, neuromelanin- and iron-sensitive MRI, and multiparametric MRI of SNpc microstructure (PMID: 42691220). Molecular biomarker: CSF α-synuclein SAA/RT-QuIC (sens ~93–95%, spec ~94%; F005) and CSF neurofilament light (NfL) to differentiate PD from atypical parkinsonism (PMID: 41324773); skin/gut tissue SAA. Genetic testing: targeted single-gene or panels (GBA1, LRRK2, SNCA, PRKN, PINK1, PARK7, VPS35), with WES/WGS for early-onset/familial cases (GTR, GeneReviews). Differential diagnosis: essential tremor, drug-induced parkinsonism, MSA, PSP, corticobasal degeneration, DLB, vascular parkinsonism — distinguished by red flags, imaging, and SAA strain typing. Screening: no population screening; prodromal risk estimation via MDS Prodromal Criteria combining RBD, hyposmia, constipation, DaT, and genetics.

11. Outcome / Prognosis

PD is not directly fatal but reduces life expectancy, chiefly via complications (aspiration pneumonia, falls/fractures, immobility). Mortality: annual mortality in a community PD cohort ~10.5% (95% CI 8.7–12.3%), with older age at onset predicting death and dementia (PMID: 41944089). Dementia: incident dementia ~5%/year in community PD. Morbidity: progressive disability, motor fluctuations, dyskinesia, and non-motor burden dominate. Prognostic factors: older onset age, GBA1 severe variants (faster cognitive/autonomic decline), postural-instability-gait-dominant subtype, early cognitive impairment/RBD; amantadine use was historically associated with improved survival (PMID: 8649547). Prognostic biomarkers: CSF NfL (progression), α-syn SAA positivity/strain, and genotype.

12. Treatment

Pharmacotherapy (symptomatic; NCIT anchors): levodopa/carbidopa (dopamine precursor; NCIT:C29159/levodopa) — most effective; dopamine agonists (pramipexole, ropinirole, rotigotine, apomorphine; non-ergot preferred, lower dyskinesia odds OR ~0.21 but higher impulse-control-disorder risk; PMID: 35527736); MAO-B inhibitors (selegiline, rasagiline, safinamide); COMT inhibitors (entacapone, opicapone — sustained motor benefit over 76 weeks, PMID: 41995421); amantadine (NMDA antagonist, anti-dyskinesia); anticholinergics (tremor). Device-aided/advanced therapies (advanced PD): subthalamic or GPi deep brain stimulation (STN-DBS best-evidenced), levodopa-carbidopa intestinal gel (LCIG), subcutaneous apomorphine/foslevodopa infusion, and MRI-guided focused ultrasound (MRgFUS) for tremor (PMID: 35791767; PMID: 35791766). Advanced-therapy referral guided by the 5-2-1 rule / MANAGE-PD tool (PMID: 42656222). Supportive/rehab: physiotherapy, occupational and speech therapy, exercise. Neuropsychiatric management: quetiapine/clozapine for psychosis; dopamine-agonist reduction for impulse-control disorders (PMID: 39046524). Experimental / disease-modifying: anti-α-synuclein antibodies (prasinezumab, cinpanemab — failed Phase II, F006); repurposed candidates (GLP-1 agonists, ambroxol, iron chelators, c-Abl inhibitors, statins, calcium-channel blockers; PMID: 39914809). Pharmacogenomics: COMT/dopaminergic metabolism variants may influence response (not definitively established here). No approved DMT exists.

13. Prevention

Primary prevention: risk-factor modification — physical activity, caffeine, avoidance of pesticide exposure; no vaccine applies. Secondary prevention: prodromal detection (RBD clinics, hyposmia/DaT/SAA screening) enables early intervention research, though no proven neuroprotective agent yet exists. Tertiary prevention: fall prevention, aspiration/pneumonia management, treatment of motor/non-motor complications, avoidance of ICD-triggering medications. Genetic counseling: offered for monogenic families and GBA1/LRRK2 carriers, emphasizing incomplete, age-dependent penetrance. Public-health/environmental: occupational pesticide-exposure reduction is the most actionable environmental lever (F003).

14. Other Species / Natural Disease

No natural, faithful spontaneous PD occurs in non-human species; naturally occurring aged non-human primates and some rodents show partial nigral dopamine decline but not full Lewy pathology. Orthologous genes exist across mammals (mouse Snca, Lrrk2, Prkn, Pink1, Park7, Gba1) and invertebrates (Drosophila parkin/PINK1; C. elegans homologs), enabling comparative study. Zoonotic/transmission concepts do not apply (PD is non-infectious), though prion-like α-synuclein spread is a mechanistic — not epidemiological — parallel. Veterinary PD as a natural disease is not established (NCBI Taxonomy; OMIA).

15. Model Organisms

Toxin-induced models: MPTP (mouse/non-human primate), 6-OHDA (rat), rotenone, paraquat — reproduce nigrostriatal dopaminergic loss and motor deficits but incompletely model Lewy pathology and are criticized as poor predictors of clinical translation (PMID: 42459575). Genetic models: SNCA A53T transgenics; LRRK2, Parkin, PINK1, DJ-1 knockouts/knock-ins — often show mild phenotypes. α-synuclein preformed-fibril (PFF) seeding models recapitulate templated aggregation, spread, and immune infiltration (PMID: 31796095). Enteric/gut models demonstrate ENS neuropathology and gut-first pathology (PMID: 33846426). Cellular models: patient iPSC-derived dopaminergic neurons and organoids. Limitations: no single model captures the full slow, age-dependent, multi-system human disease; each addresses specific mechanisms (toxicity, aggregation, spread, or genetics). Resources: MGI, RGD, ZFIN, FlyBase, WormBase, Alliance of Genome Resources.

Mechanistic Model / Interpretation

The nine findings assemble into a coherent, branching causal narrative. A converging upstream lesion — genetic (mitophagy/lysosomal genes), environmental (toxins, aging), or their interaction — cripples the two cellular systems that keep dopaminergic neurons healthy: mitochondrial quality control (PINK1/Parkin, with LRRK2 and VPS35 feeding in) and autophagy–lysosomal clearance (GBA1). The result is accumulation and misfolding of α-synuclein, the molecular linchpin. Misfolded α-synuclein then acts in three reinforcing ways: it seeds further aggregation and spreads prion-like from gut to brain along the vagus nerve (explaining Braak caudorostral staging and the body-first subtype), it functions as a DAMP that ignites neuroinflammation (microglia, A1 astrocytes, α-syn-specific T cells, BBB breakdown), and it forms Lewy bodies that mark dying neurons. Selective SNpc dopaminergic death depletes striatal dopamine and unbalances basal-ganglia circuitry, yielding the cardinal motor syndrome; parallel degeneration in olfactory, brainstem, enteric, and cortical systems produces the prodromal and non-motor spectrum.

Layer	Upstream driver	Downstream consequence	Key evidence
Genetic	SNCA, LRRK2, VPS35, PRKN, PINK1, DJ-1, GBA1	Mitophagy + lysosomal failure	F002, F004
Environmental	Pesticides, aging (× genotype)	Oxidative stress, α-syn burden	F003
Molecular	α-synuclein misfolding/aggregation	Lewy bodies, seeds	F001, F005
Propagation	Prion-like gut→brain spread	Braak staging, body-first PD	F008
Immune	α-syn DAMP, Th1/Th17, microglia	Amplified neuronal death	F007
Cellular	SNpc dopaminergic death	Striatal dopamine depletion	F001
Clinical	Basal-ganglia dysfunction	Motor + non-motor syndrome	F001, F009

This model directly explains the therapeutic impasse (F006): drugs targeting a single downstream node (extracellular α-synuclein) after most neurons are already lost, measured with insensitive scales, cannot slow a multi-loop, largely intracellular process — arguing for earlier, multi-target, biomarker-guided intervention.

Evidence Base

Finding	Primary PMIDs	Evidence type	Role
F001 Neuropathology	41904982, 35362115, 40868900	Human/review	Defines core lesion
F002 Genetics	24262182, 22806825, 22166458	Human/review	Architecture
F003 GxE	38820021, 40107260, 31706021, 28189372, 23055790	Human epi	Risk/protective + interaction
F004 Mitophagy	42681746, 41164908	In vitro/model	Mechanistic convergence
F005 SAA diagnostic	42141805, 41324773, 41604609, 42201636	Human dx	Biomarker accuracy + caveats
F006 No DMT	42227981, 41702332, 42495570, 42459575, 39914809	Clinical trials	Therapeutic gap
F007 Neuroinflammation	31796095, 38788538, 41735220, 41806646	Model/human	Immune amplification
F008 Gut-brain spread	41052745, 37873268, 36098886	Human/model	Propagation/staging
F009 GBA1-PD	42085646, 42127935, 39927608	Human registry	Penetrance/prognosis

All quoted snippets above are verbatim from the cited abstracts. The evidence spans human clinical/epidemiological studies (F001–F003, F005, F006, F009), model-organism and in vitro mechanistic work (F004, F007, F008), and systematic reviews/meta-analyses (F003, F005, F006).

Limitations and Knowledge Gaps

Prion-like spread (F008) rests substantially on model-organism and tissue-correlation data; direct causal demonstration of gut-origin spread in living humans remains inferred, not proven, and body-first vs brain-first subtyping is still being validated.
SAA (F005) shows excellent accuracy but significant inter-laboratory/protocol variability (DLB sensitivity 55–100% across labs); harmonization is required before universal clinical deployment, and the assay reports presence, not quantity or stage, of pathology.
Penetrance estimates (F009) derive partly from Gaucher (biallelic GBA1) registries and may not generalize to heterozygous idiopathic-PD carriers; LRRK2 penetrance varies by ancestry and environment.
Therapeutic failures (F006) cannot yet distinguish a wrong target from wrong timing/insensitive endpoints; the competing "Single-Neuron Degeneration"/metabolic hypothesis is plausible but unproven.
No molecular data were analyzed de novo in this investigation; findings are literature-synthesized. Quantitative epidemiology (exact prevalence/incidence per 100,000) was not fully extracted and should be sourced from GBD for the KB entry.
Sex, ancestry, and health-equity dimensions (male predominance; disparities in LGBTQ+ and minority populations, PMID: 42707080) are under-quantified here.

Proposed Follow-up Experiments / Actions

Extract quantitative epidemiology (age-specific prevalence/incidence per 100,000, DALYs, sex ratios) from GBD 2021 and Orphanet to complete Section 9 of the KB entry.
Cross-tabulate variant-level annotations (GBA1, LRRK2, SNCA) with ClinVar/gnomAD allele frequencies and ACMG classifications for a structured pathogenic-variant table.
Map the causal chain to explicit ontology triples (gene → GO process → CL cell type → UBERON site → HP phenotype) for machine-readable KB ingestion.
Add a biomarker-timing analysis: compile SAA/DaT/NfL positivity as a function of prodromal-to-clinical conversion to define intervention windows.
Systematically catalog active disease-modifying trials (GLP-1 agonists, ambroxol, LRRK2 kinase inhibitors, ASOs) with NCT identifiers for the treatment section.
Formalize body-first vs brain-first subtyping evidence and its diagnostic/prognostic implications as testable hypotheses for future iterations.

Report compiled from 5 research iterations; 9 confirmed findings; 65 papers reviewed. All statistical claims and quotations are anchored to the cited PMIDs.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	50
Resolved	50
Unresolved (possible confabulation)	0
Unverifiable	0
Quoted claims checked	1
Quoted claims found in source	1
Quoted claims not found in source	0
References weighed for topical relevance	50
On topic	14
Off topic	0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	42
Resolved	33
Unresolved (possible confabulation)	0
Obsolete	1
Unverifiable	8
Terms whose name was checked	26
Terms named correctly	20
Terms named as a different term	3
Terms whose name is worth a second look	3

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

MONDO:0005180 (3 mentions) - the report calls it "if available"; MONDO calls it Parkinson disease
CHEBI:8148 (1 mention) - the report calls it "rotenone"; CHEBI calls it CHEBI_8148
CHEBI:27958 (1 mention) - the report calls it "nicotine/tobacco"; CHEBI calls it cocaine

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

CHEBI:8148 (CHEBI_8148) (1 mention) - replaced by CHEBI:28475

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

GO:0000422 (1 mention) - the report calls it "mitophagy"; GO calls it autophagy of mitochondrion, and lists "mitophagy" among its other names
CL:0000624 (1 mention) - the report calls it "CD4+ T cell"; CL calls it CD4-positive, alpha-beta T cell
CL:0000625 (1 mention) - the report calls it "CD8+ T cell"; CL calls it CD8-positive, alpha-beta T cell

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.

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Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Environmental Factors

Biochemical Markers

Diagnosis

Stages

Prevalence

Related Datasets

Experimental Models

Animal Models

Computational Models

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References & Deep Research

References

Deep Research

Disorder

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Citation Inventory (for evidence mapping)

Parkinson's Disease: Comprehensive Disease Characteristics Report

Summary

Key Findings

F001 — Core neuropathology: nigrostriatal dopaminergic degeneration plus α-synuclein Lewy bodies

F002 — Genetic architecture: monogenic genes plus incomplete-penetrance risk variants

F003 — Gene–environment interaction: pesticide exposure sharply raises PD odds in GBA1 carriers

F004 — Monogenic genes converge on impaired mitophagy / mitochondrial quality control

F005 — α-synuclein seed amplification assay (SAA/RT-QuIC) is a high-accuracy molecular diagnostic

F006 — No disease-modifying therapy exists; α-synuclein antibodies failed Phase II

F007 — Neuroinflammation and adaptive immunity contribute to dopaminergic neurodegeneration

F008 — Prion-like gut-to-brain α-synuclein propagation underlies caudorostral Braak staging

F009 — GBA1-PD: age-dependent penetrance and a more aggressive phenotype

Detailed Section Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic / Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology — Ordered Causal Chain

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Obsolete terms

Terms whose name is worth a second look

Prefixes with no resolver