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Classifications

Harrison's Part

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Inheritance

1

Autosomal recessive inheritance HP:0000007

PARK-PRKN is inherited in an autosomal recessive manner; affected individuals carry biallelic (homozygous or compound heterozygous) pathogenic PRKN variants. Heterozygous carriers are generally unaffected, although heterozygosity has been proposed as a Parkinson disease risk factor.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:20301651 SUPPORT Human Clinical

"PARK-PRKN is inherited in an autosomal recessive manner."

GeneReviews states the mode of inheritance directly, supporting the HP:0000007 binding.

PMID:20301651 SUPPORT Human Clinical

"The diagnosis of PARK-PRKN is established in a proband with suggestive findings and biallelic pathogenic variants in PRKN identified by molecular genetic testing."

Confirms that two pathogenic PRKN alleles are required, i.e. recessive rather than dominant gene action.

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Discussions and Knowledge Gaps

2

Why does germline parkin knockout in mice fail to reproduce the substantia nigra pars compacta dopaminergic neuron loss that is the defining neuropathology of human PARK-PRKN, and does this reflect species-specific compensation, insufficient lifespan/oxidative burden, or a genuinely different human disease mechanism?

HUMAN MODEL MISMATCH OPEN hmm_prkn_knockout_mouse_no_nigral_degeneration

Attached to

pathophysiology#Accumulation of Damaged Mitochondria pathophysiology#Oxidative Stress and Respiratory Chain Deficiency pathophysiology#Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta

This is a textbook human-model mismatch and it sits precisely on the load-bearing edge of the pathograph. Parkin-null mice faithfully reproduce the UPSTREAM biology - impaired mitochondrial respiration, reduced complex I and IV subunits, reduced antioxidant capacity, increased protein and lipid peroxidation, altered striatal dopamine handling and nigrostriatal behavioural deficits - yet the number of dopaminergic neurons in the substantia nigra remains NORMAL up to 24 months of age. Human biallelic parkin carriers, by contrast, show nigral neuronal loss as severe as idiopathic Parkinson disease at autopsy. Evidence is therefore not absent (which would make this a KNOWLEDGE_GAP) but present-and-discordant: the mouse establishes the mitochondrial/oxidative arm while failing to translate it into the cell-death endpoint that defines the human disease. The mismatch has direct consequences for the knowledge base - it is why the edge from "Oxidative Stress and Respiratory Chain Deficiency" to "Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta" in this entry is typed INDIRECT_UNKNOWN_INTERMEDIATES rather than DIRECT - and for translation, since preclinical efficacy in this model cannot be read as protection against nigral degeneration. Candidate explanations include rodent lifespan being too short to accumulate the required oxidative/mtDNA burden, redundancy from other mitochondrial quality-control ligases, and species differences in nigral dopaminergic neuron vulnerability (pacemaking calcium load, neuromelanin, axonal arbor size).

Proposed experiments

Isogenic patient-derived iPSC nigral dopaminergic neuron survival under chronic mitochondrial stress

exp_prkn_ipsc_nigral_neuron_survival

Differentiate midbrain dopaminergic neurons from PRKN biallelic patient iPSCs and isogenic gene-corrected controls, apply chronic low-grade mitochondrial stress and extended culture, and measure mitophagic flux, mtDNA damage/release, cGAS-STING activation and neuron survival. This tests directly whether human nigral dopaminergic neurons, unlike mouse ones, convert the parkin-loss mitochondrial phenotype into cell death, and isolates whether the missing factor is cell-intrinsic species biology rather than duration of exposure.

Stereological nigral counts in aged and mitochondrially stressed parkin-null models

exp_prkn_aged_stressed_model_nigral_counts

Perform blinded stereological tyrosine-hydroxylase-positive nigral neuron counts in parkin-null animals aged to the limit of lifespan and/or sensitized with an independent mitochondrial-stress burden, in parallel with longitudinal pS65-ubiquitin and cell-free mtDNA measurements. A positive result would support the "insufficient cumulative burden" explanation; a persistently negative result would argue for genuine species-specific compensation and would strengthen the case for human-based models.

Show evidence (4 references)

PMID:12930822 SUPPORT Model Organism

"The number of dopaminergic neurons in the substantia nigra of parkin-/- mice, however, is normal up to the age of 24 months, in contrast to the substantial loss of nigral neurons characteristic of Parkinson's disease."

The primary statement of the mismatch: the mouse knockout does not reproduce the defining human nigral degeneration even at 24 months.

PMID:12930822 SUPPORT Model Organism

"Together these findings provide the first evidence for a novel role of parkin in dopamine regulation and nigrostriatal function, and a non-essential role of parkin in the survival of nigral neurons in mice."

Explicitly frames parkin as non-essential for nigral neuron survival in mice, in direct tension with the human neuropathology.

PMID:14985362 SUPPORT Model Organism

"provide the first direct evidence of mitochondrial dysfunction and oxidative damage in the absence of nigral degeneration in a genetic mouse model of Parkinson's disease"

Confirms the dissociation: the upstream mitochondrial/oxidative phenotype is faithfully modelled while the downstream degeneration is not.

+ 1 more reference

What makes substantia nigra pars compacta dopaminergic neurons - and specifically the ventral tier - selectively vulnerable to loss of parkin-dependent mitophagy, when parkin is broadly expressed and the PINK1-parkin pathway operates in all cell types?

KNOWLEDGE GAP OPEN gap_prkn_nigral_selectivity

Attached to

pathophysiology#Impaired Mitophagy pathophysiology#Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta

Parkin is expressed in many human tissues, yet biallelic loss produces a strikingly organ- and even sub-nucleus-restricted phenotype: severe ventral nigral loss with relative dorsal-tier preservation, mild locus coeruleus and dorsal vagal involvement, and sparing of the nucleus basalis of Meynert and raphe. No mechanism in this entry's pathograph explains that selectivity; the mitophagy defect as modelled is cell-type agnostic. Resolving this is the difference between a generic mitochondrial-quality-control story and an account that predicts which neurons die. Candidate but unresolved factors include the exceptionally large unmyelinated axonal arbor and consequent bioenergetic load of nigral dopaminergic neurons, autonomous pacemaking with sustained calcium influx, dopamine metabolism as an endogenous oxidant source, and regional differences in baseline mitophagic flux.

Show evidence (2 references)

PMID:9560156 SUPPORT Human Clinical

"A 4.5-kilobase transcript that is expressed in many human tissues but is abundant in the brain, including the substantia nigra"

Establishes that parkin expression is broad, so expression alone does not account for the restricted phenotype.

PMID:23459986 SUPPORT Human Clinical

"Mild neuronal loss was identified in the locus coeruleus and dorsal motor nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe nucleus, or other brain regions."

Documents the fine-grained regional selectivity that requires explanation.

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Pathophysiology

13

PRKN Biallelic Loss of Function

Homozygous or compound heterozygous loss-of-function PRKN alleles - most often whole-exon deletions or duplications, and less often point mutations - abolish functional parkin, an E3 ubiquitin ligase. This is the initiating molecular lesion of PARK-PRKN.

PRKN hgnc:8607

parkin ubiquitin protein ligase activity GO:0061630 ↓ DECREASED

Downstream

Failure of Phospho-Ubiquitin-Dependent Parkin Recruitment and E3 Ligase Activation With no functional parkin protein, the recruitment/activation step of the PINK1-parkin axis cannot proceed regardless of an intact upstream PINK1 signal.

Show evidence (2 references)

PMID:9560156 SUPPORT Human Clinical

"encoding a protein of 465 amino acids with moderate similarity to ubiquitin at the amino terminus and a RING-finger motif at the carboxy terminus"

Identifies parkin as a RING-finger (E3 ubiquitin ligase family) protein disrupted by deletion in AR-JP patients.

PMID:24784582 SUPPORT In Vitro

"PINK1 (PTEN induced putative kinase 1) and PARKIN (also known as PARK2) have been identified as the causal genes responsible for hereditary recessive early-onset Parkinsonism."

Confirms PRKN/PARK2 as a causal gene for hereditary recessive early-onset parkinsonism and situates it in the PINK1-parkin axis.

Mitochondrial Depolarization

Loss of inner mitochondrial membrane potential marks an individual mitochondrion as damaged. This is the upstream damage state that the PINK1-parkin quality-control system detects; it is scale-MOLECULAR and is modelled separately from the PINK1 sensing response it triggers.

mitochondrial depolarization GO:0051882

Downstream

PINK1 Accumulation on the Outer Mitochondrial Membrane Depolarization blocks the voltage-dependent proteolysis that normally keeps outer-membrane PINK1 low, so PINK1 accumulates selectively on the depolarized organelle.

Show evidence (1 reference)

PMID:20126261 SUPPORT In Vitro

"Parkin is selectively recruited to damaged mitochondria that have lost their membrane potential"

Establishes loss of membrane potential as the damage state that the pathway acts on.

PINK1 Accumulation on the Outer Mitochondrial Membrane

Full-length PINK1 accumulates on the outer membrane of the depolarized organelle with its kinase domain facing the cytosol. This is the damage-sensing step that flags an individual mitochondrion for disposal and is the immediate upstream requirement for parkin recruitment.

PINK1 kinase autophosphorylation and stabilization GO:0018105

Downstream

Failure of Phospho-Ubiquitin-Dependent Parkin Recruitment and E3 Ligase Activation Accumulated PINK1 is necessary and sufficient to recruit parkin; in PARK-PRKN the PINK1 signal is generated normally but has no competent effector.

Show evidence (1 reference)

PMID:20126261 SUPPORT In Vitro

"Selective accumulation of PINK1 on the impaired mitochondria recruits Parkin, and Parkin, in turn, induces the degradation of the damaged mitochondria."

States the sensing step and its immediate consequence for parkin recruitment.

Failure of Phospho-Ubiquitin-Dependent Parkin Recruitment and E3 Ligase Activation

Mitochondrial PINK1 phosphorylates ubiquitin at Ser65. Phospho-ubiquitin is the genuine parkin activator: it binds parkin allosterically, unlocking the autoinhibited catalytic cysteine, while PINK1-dependent phosphorylation of parkin itself completes full activation. In PARK-PRKN this convergence step fails because parkin is absent or catalytically dead, so the Ser65 phospho-ubiquitin signal is generated but not transduced.

PINK1-mediated ubiquitin Ser65 phosphorylation GO:0018105

parkin E3 ubiquitin ligase activation GO:0061630 ↓ DECREASED

Downstream

Loss of Ubiquitination of Outer Mitochondrial Membrane Substrates Activated parkin is the enzyme that transfers ubiquitin onto outer-membrane proteins; without activation this transfer does not occur.

Show evidence (3 references)

PMID:24784582 SUPPORT In Vitro

"Here we report that ubiquitin is the genuine substrate of PINK1. PINK1 phosphorylated ubiquitin at Ser 65 both in vitro and in cells"

Identifies ubiquitin Ser65 as the PINK1 substrate that constitutes the activating signal.

PMID:24784582 SUPPORT In Vitro

"The phosphorylation-dependent interaction between ubiquitin and parkin suggests that phosphorylated ubiquitin unlocks autoinhibition of the catalytic cysteine."

Provides the allosteric mechanism by which phospho-ubiquitin activates parkin's latent E3 activity.

PMID:24784582 SUPPORT In Vitro

"PINK1 acts as an upstream factor for parkin and is essential both for the activation of latent E3 parkin activity and for recruiting parkin onto depolarized mitochondria."

States the epistatic ordering (PINK1 upstream of parkin) and the dual recruitment/activation role.

Loss of Ubiquitination of Outer Mitochondrial Membrane Substrates

Activated parkin decorates outer mitochondrial membrane proteins with ubiquitin chains, which are further phosphorylated by PINK1 to generate a feed-forward amplification loop and to build the autophagy-receptor recognition signal on the damaged organelle. In PARK-PRKN this ubiquitin coat is not deposited, so the damaged mitochondrion is never tagged for disposal.

ubiquitination of outer mitochondrial membrane substrates GO:0016567 ↓ DECREASED

Downstream

Impaired Mitophagy The parkin-deposited ubiquitin signal is what commits the damaged mitochondrion to autophagic engulfment; its absence blocks mitophagy.

Show evidence (1 reference)

PMID:24784582 SUPPORT In Vitro

"Our results show that PINK1-dependent phosphorylation of both parkin and ubiquitin is sufficient for full activation of parkin E3 activity."

Supports that parkin E3 activity - and hence substrate ubiquitination - is the output of this module and is lost when parkin is absent.

Impaired Mitophagy

Mitophagy - the selective autophagic elimination of damaged mitochondria - is the terminal output of the PINK1-parkin axis and constitutes a mitochondrial quality-control system. Loss of parkin disables the parkin-dependent arm of this system, so damaged organelles are neither tagged nor cleared. Post-mitotic dopaminergic neurons, which cannot dilute damaged mitochondria by division, are predicted to be particularly reliant on this pathway.

dopaminergic neuron CL:0000700

mitophagy GO:0000422 ↓ DECREASED

Downstream

Accumulation of Damaged Mitochondria Undisposed damaged mitochondria persist, with falling respiratory-chain capacity and rising reactive oxygen species and oxidative damage.

Show evidence (2 references)

PMID:20126261 SUPPORT In Vitro

"they support a novel model for the negative selection of damaged mitochondria, in which PINK1 signals mitochondrial dysfunction to Parkin, and Parkin promotes their elimination"

States the quality-control model whose parkin-dependent arm is lost in PARK-PRKN.

PMID:33029617 SUPPORT Model Organism

"Recent research in murine models suggests that parkin and PINK1 deficiency leads to impaired mitophagy, which causes the release of mitochondrial DNA (mtDNA), thereby triggering inflammation."

Frames impaired mitophagy as the consequence of parkin deficiency and links it forward to the mtDNA-release arm. Tagged MODEL_ORGANISM and quoted with its full "Recent research in murine models suggests that" lead-in, because this sentence is the authors' summary of mouse work rather than their own human cohort result. The source also treats PRKN and PINK1 deficiency jointly.

Accumulation of Damaged Mitochondria

Without parkin-dependent clearance, dysfunctional mitochondria are not removed from the network and accumulate in the cell. This is the direct organelle-level consequence of the mitophagy block, modelled separately from the oxidative/bioenergetic damage it subsequently produces.

mitochondrion organization GO:0007005 ⚠ ABNORMAL

Downstream

Oxidative Stress and Respiratory Chain Deficiency Retained dysfunctional mitochondria have reduced respiratory-chain capacity and generate oxidative damage.

Cytosolic and Circulating mtDNA Release Damaged, uncleared mitochondria release mitochondrial DNA, which acts as a damage-associated molecular pattern.

Show evidence (1 reference)

PMID:14985362 SUPPORT Model Organism

"The combination of proteomic, genetic, and physiological analyses reveal an essential role for parkin in the regulation of mitochondrial function"

Establishes that loss of parkin degrades the mitochondrial population in vivo.

Oxidative Stress and Respiratory Chain Deficiency

In parkin-null mice the retained dysfunctional mitochondria manifest as reduced abundance of complex I and complex IV subunits, measurably reduced respiratory capacity of striatal mitochondria, reduced antioxidant defences, and increased protein and lipid peroxidation. Chronic oxidative burden is the proposed proximate injury to dopaminergic neurons.

oxidative stress response GO:0006979 ⚠ ABNORMAL

striatum UBERON:0002435

Downstream

Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta Chronic mitochondrial dysfunction and oxidative damage are the proposed cell-autonomous driver of nigral dopaminergic degeneration. The link is marked INDIRECT_UNKNOWN_INTERMEDIATES deliberately: parkin-null mice show the mitochondrial and oxidative phenotype WITHOUT nigral neuron loss, so the intermediate steps that convert this cellular stress into human dopaminergic cell death are not established (see the HUMAN_MODEL_MISMATCH discussion on this entry).

Show evidence (1 reference)

PMID:14985362 SUPPORT Model Organism

"parkin-/- mice showed decreased serum antioxidant capacity and increased protein and lipid peroxidation"

Demonstrates the oxidative-damage arm downstream of parkin loss in vivo.

Cytosolic and Circulating mtDNA Release

Mitochondrial DNA escapes from uncleared damaged mitochondria. In humans this is measurable as increased circulating cell-free mtDNA in carriers of biallelic or heterozygous PRKN/PINK1 mutations relative to idiopathic Parkinson disease, whereas unaffected heterozygous carriers have control-level concentrations. Released mtDNA is the damage-associated molecular pattern that the downstream innate immune sensor detects.

Downstream

cGAS-STING Innate Immune Activation Cytosolic mtDNA is sensed by cGAS-STING, converting the organelle defect into an inflammatory signal.

Show evidence (1 reference)

PMID:33029617 SUPPORT Human Clinical

"By contrast, circulating cell-free mtDNA concentrations in unaffected heterozygous carriers of PRKN/PINK1 mutations were comparable to control levels"

The authors' own human cohort measurement, showing mtDNA release tracks affected status rather than carrier status alone.

cGAS-STING Innate Immune Activation

Sensing of released mtDNA drives type I interferon and interleukin-6 responses. In humans, patients with biallelic PRKN/PINK1 mutations have elevated serum IL-6 relative to healthy controls, with an apparent gene-dosage effect between biallelic and heterozygous carriers, and IL-6 correlates with disease duration in mutation carriers but not in idiopathic Parkinson disease. Marked PROVISIONAL: the human data are serum biomarker associations rather than demonstrations of causal neuroinflammatory neurodegeneration.

interleukin-6 production GO:0032755 ↑ INCREASED type I interferon production GO:0032606 ↑ INCREASED

Downstream

Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta Chronic mtDNA-driven innate immune activation is hypothesized to contribute to dopaminergic neurodegeneration. This edge is the least established in the graph - the supporting human data are peripheral serum biomarkers, not CNS neuropathology.

Show evidence (2 references)

PMID:33029617 SUPPORT Human Clinical

"elevated IL6 levels in patients with biallelic PRKN/PINK1 mutations compared to healthy control subjects in a German cohort, supporting the concept of a role for inflammation in PRKN/PINK1-linked Parkinson's disease"

The authors' own human cohort result: an inflammatory arm specifically in biallelic PRKN/PINK1 patients, validated in a second Italian cohort.

PMID:33029617 SUPPORT Human Clinical

"a correlation between IL6 levels and disease duration in carriers of PRKN/PINK1 mutations, while no such association was observed for idiopathic Parkinson's disease patients"

Human cohort result distinguishing the PRKN/PINK1 inflammatory signature from idiopathic Parkinson disease.

Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta

Dopaminergic neurons of the substantia nigra pars compacta degenerate. In autopsy-confirmed parkin disease the magnitude of nigral neuronal loss is as severe as in idiopathic Parkinson disease, but the topography differs: loss is predominantly ventral with relative preservation of the dorsal tier. Mild neuronal loss also occurs in the locus coeruleus and dorsal motor nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe nucleus, or other brain regions - a markedly more restricted distribution than in idiopathic Parkinson disease.

nigral dopaminergic neuron CL:0000700

dopaminergic neuron apoptosis GO:0051402 ↑ INCREASED

substantia nigra pars compacta UBERON:0001965

Downstream

Nigrostriatal Dopamine Deficiency Loss of nigral dopaminergic neurons removes the dopaminergic projection to the striatum, producing measurable presynaptic striatal dopaminergic denervation.

Show evidence (2 references)

PMID:23459986 SUPPORT Human Clinical

"Neuronal counts in the substantia nigra pars compacta revealed that neuronal loss in the parkin cases was as severe as that seen in PD, but relative preservation of the dorsal tier was seen in comparison with PD"

Quantitative human neuropathology establishing both the severity and the distinctive ventral-predominant topography of nigral loss.

PMID:23459986 SUPPORT Human Clinical

"Mild neuronal loss was identified in the locus coeruleus and dorsal motor nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe nucleus, or other brain regions."

Documents the restricted extranigral distribution that distinguishes parkin disease from idiopathic Parkinson disease.

Nigrostriatal Dopamine Deficiency

Degeneration of the nigrostriatal projection produces severe striatal dopamine deficiency, quantified in parkin-mutation patients by 18F-dopa PET as roughly 28% of control putaminal and 44% of control caudate uptake. This deficiency is the direct target of dopamine-replacement therapy and explains the excellent levodopa responsiveness of the disorder.

dopaminergic synaptic transmission GO:0001963 ↓ DECREASED

striatum UBERON:0002435

Downstream

Parkinsonism Striatal dopamine deficiency produces the cardinal motor syndrome of bradykinesia, rest tremor and rigidity.

Show evidence (1 reference)

PMID:10994015 SUPPORT Human Clinical

"Parkin gene mutations cause a form of early-onset autosomal recessive PD with neuronal loss in the substantia nigra and no Lewy bodies."

Confirms both the nigral degeneration underlying the dopamine deficit and the Lewy-body-negative pathology in the same imaged patient group.

Parkinsonism

The clinical syndrome: bradykinesia with resting tremor and rigidity, typically with early lower-limb dystonia, hyperreflexia, symmetric involvement, an excellent and sustained levodopa response, and early levodopa-induced dyskinesias. Progression is slow and cognitive decline is no more frequent than in the general population.

Show evidence (1 reference)

PMID:10824074 SUPPORT Human Clinical

"they were more likely to have symmetric involvement and dystonia at onset, to have hyperreflexia at onset or later, to have a good response to levodopa therapy, and to have levodopa-induced dyskinesias during treatment"

Defines the distinguishing clinical signature of parkin-mutation patients relative to mutation-negative early-onset Parkinson disease.

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Histopathology

1

Lewy-Body-Negative Nigral Degeneration

The distinguishing neuropathology of PARK-PRKN. Severe neuronal loss in the substantia nigra pars compacta occurs in the ABSENCE of the alpha-synuclein Lewy-body pathology that defines idiopathic Parkinson disease. Where Lewy bodies have been found in autopsy-confirmed parkin cases they were sparse and present in a minority of cases. The loss is topographically restricted - predominantly ventral tier, with relative dorsal-tier preservation, and limited extranigral involvement. This makes parkin disease a clinicopathologically distinct entity rather than simply an early-onset variant of idiopathic Parkinson disease, and is the single strongest argument for curating it as a separate dismech entry.

Show evidence (4 references)

PMID:23459986 SUPPORT Human Clinical

"These findings support the notion that parkin disease is characterized by a more restricted morphologic abnormality than is found in PD, with predominantly ventral nigral degeneration and absent or rare Lewy bodies."

The definitive statement of the distinguishing neuropathology from a controlled autopsy series (5 parkin cases vs 5 pathologically confirmed PD cases and 4 controls).

PMID:23459986 SUPPORT Human Clinical

"Sparse Lewy bodies were identified in 2 cases (brainstem and cortex)."

Marked PARTIAL because it qualifies the claim: Lewy bodies are usually but not invariably absent - 2 of 5 cases had sparse Lewy bodies. Curated explicitly so the entry does not overstate "Lewy-body negative" as absolute.

PMID:10994015 SUPPORT Human Clinical

"Parkin gene mutations cause a form of early-onset autosomal recessive PD with neuronal loss in the substantia nigra and no Lewy bodies."

Independent statement of the nigral-loss-without-Lewy-bodies pathology.

+ 1 more reference

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

9

Musculoskeletal 1

Rigidity HP:0002063

Show evidence (1 reference)

PMID:20301651 SUPPORT Human Clinical

"PRKN-related early-onset Parkinson disease (PARK-PRKN) is characterized by the cardinal signs of Parkinson disease (PD): bradykinesia, resting tremor, and rigidity."

GeneReviews lists rigidity as a cardinal sign.

Nervous System 4

Bradykinesia HP:0002067

Show evidence (1 reference)

PMID:20301651 SUPPORT Human Clinical

"PRKN-related early-onset Parkinson disease (PARK-PRKN) is characterized by the cardinal signs of Parkinson disease (PD): bradykinesia, resting tremor, and rigidity."

GeneReviews lists bradykinesia as a cardinal sign. No frequency band is asserted because this is a definitional statement, not a measured proportion.

Resting Tremor HP:0002322

Show evidence (2 references)

PMID:20301651 SUPPORT Human Clinical

"PRKN-related early-onset Parkinson disease (PARK-PRKN) is characterized by the cardinal signs of Parkinson disease (PD): bradykinesia, resting tremor, and rigidity."

GeneReviews lists resting tremor as a cardinal sign.

PMID:23459986 SUPPORT Human Clinical

"Presenting signs in the parkin disease cases were hand or leg tremor often combined with dystonia."

Autopsy-confirmed series describing tremor (with dystonia) as the typical presenting sign.

Hyperreflexia FREQUENT HP:0001347

Show evidence (2 references)

PMID:20301651 SUPPORT Human Clinical

"Clinical findings vary; hyperreflexia is common."

Supports both the association and the FREQUENT band. The GeneReviews term "common" maps to FREQUENT (30-79%) under the project's literature-term-to-enum mapping table.

PMID:10824074 SUPPORT Human Clinical

"to have hyperreflexia at onset or later"

Independent confirmation that hyperreflexia is over-represented in parkin-mutation carriers.

Levodopa-Induced Dyskinesia FREQUENT HP:0100660

Show evidence (2 references)

PMID:20301651 SUPPORT Human Clinical

"Dyskinesia as a result of treatment with levodopa frequently occurs."

Supports both the association and the FREQUENT band; "frequently occurs" maps to FREQUENT (30-79%) under the project's mapping table.

PMID:10824074 SUPPORT Human Clinical

"to have levodopa-induced dyskinesias during treatment"

Confirms the over-representation of levodopa-induced dyskinesias in parkin-mutation carriers.

Other 4

Lower-Limb Dystonia at Onset Leg dystonia HP:0031959

Show evidence (2 references)

PMID:20301651 SUPPORT Human Clinical

"Lower-limb dystonia may be a presenting sign"

GeneReviews identifies lower-limb dystonia as a presenting sign. No frequency band is asserted: "may be" does not map to a FrequencyEnum value.

PMID:10824074 SUPPORT Human Clinical

"they were more likely to have symmetric involvement and dystonia at onset"

Comparative evidence that dystonia at onset discriminates parkin-mutation carriers from non-carriers with early-onset Parkinson disease.

Excellent and Sustained Levodopa Response Parkinsonism with favorable response to dopaminergic medication HP:0002548

Show evidence (2 references)

PMID:10824074 SUPPORT Human Clinical

"to have a good response to levodopa therapy"

Parkin-mutation carriers were significantly more likely than non-carriers to have a good levodopa response.

PMID:29644727 SUPPORT Human Clinical

"an overall clinically typical form of PD with excellent treatment response, dystonia and dyskinesia being relatively common and cognitive decline relatively uncommon"

Systematic review of more than 1100 patients confirming the excellent treatment response. Note the review pools Parkin, PINK1 and DJ1.

Freezing of Gait HP:0031825

Show evidence (1 reference)

PMID:23459986 SUPPORT Human Clinical

"Freezing of gait, postural deformity, and motor fluctuations were common late features."

Autopsy-confirmed parkin disease series describing late motor features. Frequency band omitted: "common late features" in a five-case series does not support a quantitative band.

Relative Cognitive Sparing

NEEDS-TERM-REQUEST (NTR). This entry deliberately carries NO `term:` binding. HPO has no positive term for "cognition preserved", and both available workarounds are wrong: binding an HP dementia term would be read by downstream tooling as the disease HAVING dementia (the opposite of the curated finding, since dismech's phenotype model has no negation slot), and binding the general parent HP:0001300 Parkinsonism - which this entry did until PR review - is misleading because it labels a cognitive observation with a motor term that is already asserted elsewhere in the entry. An unbound `preferred_term` is the honest representation: the substantive claim is carried by the description and the two evidence items. An HPO term request for a "cognitive function preserved / not more frequent than population baseline" concept would be needed to bind this properly.

Show evidence (2 references)

PMID:20301651 SUPPORT Human Clinical

"cognitive decline appears to be no more frequent than in the general population"

GeneReviews states that cognitive decline is not over-represented, supporting relative cognitive sparing.

PMID:23459986 SUPPORT Human Clinical

"No patients had any evidence of cognitive impairment or dementia."

Autopsy-confirmed series with no cognitive impairment in any of five cases.

🧬

Genetic Associations

1

PRKN (Biallelic loss-of-function variants in PRKN (formerly PARK2), encoding the RING-between-RING E3 ubiquitin ligase parkin, cause autosomal recessive juvenile/early-onset Parkinson disease. The gene lies at 6q25.2-q27, spans more than 500 kb, and has 12 exons.)

Gene: PRKN hgnc:8607 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (4 references)

PMID:9560156 SUPPORT Human Clinical

"Mutations in the newly identified gene appear to be responsible for the pathogenesis of AR-JP, and we have therefore named the protein product 'Parkin'."

The original positional-cloning report establishing PRKN/parkin as the gene underlying autosomal recessive juvenile parkinsonism.

PMID:9560156 SUPPORT Human Clinical

"The gene spans more than 500 kilobases and has 12 exons, five of which (exons 3-7) are deleted in the patient. Four other AR-JP patients from three unrelated families have a deletion affecting exon 4 alone."

Documents the gene structure and the founding observation that multi-exon and single-exon deletions - not point mutations - were the first pathogenic alleles identified, anchoring the CNV-dominant mutational spectrum.

PMID:10824074 SUPPORT Human Clinical

"Nineteen different rearrangements of exons (deletions and multiplications) and 16 different point mutations were detected."

Quantifies the DIVERSITY of the mutational spectrum in a large multicentre series: 19 distinct exonic rearrangements versus 16 distinct point mutations. Note this counts distinct variant types, NOT the share of alleles or patients attributable to each class - the abstract does not report that split - so the claim made here is only that exonic rearrangements are a large and irreducible part of the spectrum, which is why copy-number analysis is required for complete PRKN testing.

+ 1 more reference

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Medical Actions

6

Levodopa/Carbidopa

Action: Pharmacotherapy NCIT:C15986

Agent: levodopa CHEBI:15765 carbidopa CHEBI:3395

Dopamine replacement is the mainstay of therapy and PARK-PRKN responds excellently and durably, often at low doses. Carbidopa is a peripheral DOPA-decarboxylase inhibitor co-administered to reduce peripheral conversion. IMPORTANT SAFETY NOTE from the GeneReviews agents/circumstances-to-avoid section: levodopa dosing beyond what is needed for satisfactory clinical response should be avoided, because levodopa-induced dyskinesias occur frequently and early in this disorder.

Mechanism Target:

RESTORES Nigrostriatal Dopamine Deficiency — Levodopa is decarboxylated to dopamine in surviving nigrostriatal terminals and other striatal cells, replacing the missing neurotransmitter downstream of the degenerated neurons. It restores striatal dopaminergic neurotransmission without addressing the upstream mitophagy defect, which is why the response is symptomatic rather than disease-modifying.

Show evidence (1 reference)

PMID:10994015 SUPPORT Human Clinical

"representing 28% of putamen and 44% of caudate nucleus control subject values"

Quantifies the striatal dopaminergic deficit that dopamine replacement therapy compensates for.

Target Phenotypes: Bradykinesia HP:0002067 Rigidity HP:0002063 Resting tremor HP:0002322

Show evidence (3 references)

PMID:20301651 SUPPORT Human Clinical

"Treatment of manifestations: Levodopa and dopamine receptor agonists, monoamine oxidase type B inhibitors, catechol-O-methyltransferase inhibitors, amantadine, adenosine A2A receptor antagonists, anticholinergics"

GeneReviews management recommendation naming levodopa first-line.

PMID:20301651 SUPPORT Human Clinical

"Agents/circumstances to avoid: Use of levodopa therapy that exceeds the dose needed for satisfactory clinical response."

The GeneReviews drug-safety warning motivating dose restraint, given the frequent early levodopa-induced dyskinesias.

PMID:20301651 SUPPORT Human Clinical

"Dopamine-blocking therapies (both typical and atypical dopamine-blocking psychiatric medications as well as dopamine blockers for gastrointestinal causes) may exacerbate parkinsonism in individuals with PARK-PRKN and should be avoided, when possible."

Second GeneReviews drug-safety warning: dopamine-blocking agents, including antiemetics, worsen parkinsonism and should be avoided.

Deep Brain Stimulation

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

Deep brain stimulation is recommended for individuals experiencing difficulty with levodopa therapy - in PARK-PRKN typically those limited by levodopa-induced dyskinesias and motor fluctuations rather than by loss of dopaminergic responsiveness.

Target Phenotypes: Dyskinesia HP:0100660

Show evidence (1 reference)

PMID:20301651 SUPPORT Human Clinical

"deep brain stimulation for those experiencing difficulty with levodopa therapy"

GeneReviews management recommendation for DBS.

Physical, Occupational and Speech Therapy

Action: physical therapy Ontology label: Physical Therapy NCIT:C15302

Non-pharmacological rehabilitation: exercise as tolerated (aerobic, strength building and integrative), physical and occupational therapy, and speech and voice therapy. Particularly relevant here given the long disease duration and young age at onset.

Show evidence (1 reference)

PMID:20301651 SUPPORT Human Clinical

"exercise as tolerated (aerobic, strength building, and integrative); physical and occupational therapy; speech and voice therapy"

GeneReviews management recommendations for rehabilitation.

Non-Motor and Autonomic Symptom Management

Action: supportive care Ontology label: Supportive Care NCIT:C15747

PARK-PRKN care is not confined to the motor syndrome. GeneReviews specifies symptomatic treatment of constipation; urology management of genitourinary manifestations; sleep aids, minimizing caffeine, good sleep hygiene and light therapy for sleep problems; and standard treatment of orthostatic hypotension. These matter disproportionately in this disorder because onset is early and disease duration can exceed 60 years, so the cumulative non-motor burden is carried for decades.

Show evidence (1 reference)

PMID:20301651 SUPPORT Human Clinical

"symptomatic treatment of constipation; urology management of genitourinary manifestations; sleep aids, minimizing caffeine, good sleep hygiene, and light therapy for sleep problems; standard treatment of orthostatic hypotension"

The GeneReviews Management recommendations for the constipation, genitourinary, sleep and orthostatic-hypotension domains, quoted verbatim.

Cognitive and Dementia Management

Action: Pharmacotherapy NCIT:C15986

Agent: cholinesterase inhibitor NCIT:C47792

Where cognitive impairment does occur, GeneReviews recommends cognitive behavioral therapy, pharmacologic treatment, and/or a cholinesterase inhibitor as needed. Note this is an "as needed" contingency rather than an expected course: cognitive decline in PARK-PRKN is no more frequent than in the general population (see the "Relative Cognitive Sparing" phenotype), in contrast to idiopathic Parkinson disease where dementia is a common late outcome.

Show evidence (1 reference)

PMID:20301651 SUPPORT Human Clinical

"cognitive behavioral therapy, pharmacologic treatment, and/or cholinesterase inhibitor as needed for dementia"

The GeneReviews Management recommendation for cognitive/dementia care, quoted verbatim.

Genetic Counseling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Autosomal recessive recurrence counseling. Once the familial PRKN variants are known, heterozygote testing for at-risk relatives and prenatal or preimplantation genetic testing are possible.

Show evidence (2 references)

PMID:20301651 SUPPORT Human Clinical

"If both parents are known to be heterozygous for a PRKN pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being heterozygous, and a 25% chance of inheriting neither of the familial PRKN pathogenic variants."

GeneReviews recurrence-risk counseling content.

PMID:20301651 SUPPORT Human Clinical

"Once the PRKN pathogenic variants have been identified in an affected family member, heterozygote testing for at-risk relatives and prenatal/preimplantation genetic testing are possible."

GeneReviews statement on cascade and reproductive testing.

🔬

Diagnosis

2

PRKN Molecular Genetic Testing with Exon-Dosage Analysis

Diagnosis is established by identifying biallelic pathogenic PRKN variants. Because exonic deletions and duplications dominate the mutational spectrum, sequence analysis alone is insufficient and must be paired with a copy-number/dosage method (e.g. MLPA). A single heterozygous point mutation should prompt dosage testing for a second, rearrangement allele in trans.

Show evidence (3 references)

PMID:20301651 SUPPORT Human Clinical

"The diagnosis of PARK-PRKN is established in a proband with suggestive findings and biallelic pathogenic variants in PRKN identified by molecular genetic testing."

States the diagnostic standard.

PMID:10824074 SUPPORT Human Clinical

"All subjects were screened for mutations in the parkin gene with use of a semiquantitative polymerase-chain-reaction assay that simultaneously amplified several exons."

Illustrates that a dosage-sensitive (semiquantitative, multi-exon) assay rather than plain sequencing was required to detect the rearrangements that made up the majority of alleles found.

PMID:10824074 SUPPORT Human Clinical

"Accurate diagnosis of these cases cannot be based only on the clinical manifestations of the disease."

Supports the requirement for molecular confirmation rather than clinical diagnosis alone.

Periodic Neurologic, Autonomic and Cognitive Surveillance

Ongoing surveillance rather than one-off diagnosis. GeneReviews recommends neurologic examination together with assessment of autonomic function and cognitive issues every six to 12 months. The autonomic and cognitive components are the reason this is not simply motor follow-up: they are the domains that generate the non-motor management needs (constipation, genitourinary, sleep, orthostatic hypotension) curated under treatments.

neurologic examination NCIT:C81313

Show evidence (1 reference)

PMID:20301651 SUPPORT Human Clinical

"Surveillance: Neurologic examination and assessment of autonomic function and cognitive issues every six to 12 months."

The GeneReviews Surveillance recommendation, including its six-to-12-month interval, quoted verbatim.

🩻

Imaging Findings

1

Reduced Striatal 18F-Dopa Uptake

18F-dopa PET in juvenile-onset patients with parkin mutations shows a profound presynaptic dopaminergic deficit, with uptake reduced to approximately 28% of control values in the putamen and 44% in the caudate nucleus - a putamen-predominant gradient similar to idiopathic Parkinson disease.

Show evidence (2 references)

PMID:10994015 SUPPORT Human Clinical

"representing 28% of putamen and 44% of caudate nucleus control subject values"

Quantifies the imaging phenotype. Based on three cases (one familial, two sporadic), so the point estimates should be read as illustrative.

PMID:10994015 SUPPORT Human Clinical

"PD caused by parkin gene mutations is distinct from idiopathic PD on molecular grounds but has similar clinical and PET findings."

Important nuance: imaging does NOT distinguish parkin disease from idiopathic Parkinson disease - the divergence is molecular and neuropathologic.

📈

Progression

1

Age at onset

Median age at onset approximately 31 years, with a very wide reported range (1-84 years). Progression is slow and disease duration of more than 60 years has been reported, in contrast to the more rapid course typical of late-onset Parkinson disease.

Show evidence (3 references)

PMID:20301651 SUPPORT Human Clinical

"The median age at onset is 31 years (range: 1-84 years)."

GeneReviews gives the median and range of age at onset.

PMID:20301651 SUPPORT Human Clinical

"The disease is slowly progressive: a disease duration of more than 60 years has been reported."

Supports the slow rate of progression and long disease duration.

PMID:29644727 SUPPORT Human Clinical

"median age at onset of ∼30 years for carriers of at least 2 mutations in any of the 3 genes"

Independent systematic-review confirmation of the early median onset. Note the MDSGene figure pools carriers of biallelic variants in Parkin, PINK1 or DJ1 rather than PRKN alone.

📊

Prevalence

1

Worldwide

Unknown Rare

No direct population-based prevalence estimate for PARK-PRKN specifically was identified in the sources used for this entry, so only the coarse qualitative band is asserted. The rarity can be bounded indirectly: only a small minority of Parkinson disease is early-onset, and only a minority of early-onset cases carry biallelic PRKN variants (see the structured `case_fractions` on the PRKN `genetic` entry, which is the well-quantified dimension). Do not read this record as a measured rate.

Show evidence (1 reference)

PMID:22956510 SUPPORT Human Clinical

"Approximately 3.6% of patients with Parkinson's disease develop symptoms before age 45."

Supports the rarity band only indirectly. It quantifies the early-onset Parkinson disease denominator, not the prevalence of PARK-PRKN itself; PRKN-attributable cases are a minority of that already small subgroup. Marked PARTIAL because the quoted statistic does not measure this disease's occurrence.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from PRKN-Related Juvenile Parkinson Disease:

Idiopathic (late-onset) Parkinson Disease

Overlapping Features The principal differential. Distinguishing features favouring PARK-PRKN are early median onset (~31 years), lower-limb dystonia at presentation, hyperreflexia, symmetric involvement, slow progression, absence of cognitive decline, and Lewy-body-negative ventral-predominant nigral degeneration at autopsy. Critically, 18F-dopa PET does NOT separate the two entities. Curated separately in dismech as `Parkinsons_Disease` (MONDO:0005180).

Show evidence (2 references)

PMID:23459986 SUPPORT Human Clinical

"These findings support the notion that parkin disease is characterized by a more restricted morphologic abnormality than is found in PD, with predominantly ventral nigral degeneration and absent or rare Lewy bodies."

Establishes parkin disease as pathologically distinct from idiopathic Parkinson disease.

PMID:10994015 SUPPORT Human Clinical

"PD caused by parkin gene mutations is distinct from idiopathic PD on molecular grounds but has similar clinical and PET findings."

Explicitly notes that PET imaging cannot make the distinction, so molecular testing is required.

{ }

Source YAML

click to show

name: PRKN-Related Juvenile Parkinson Disease
creation_date: "2026-07-31T00:00:00Z"
description: >-
  Autosomal recessive juvenile Parkinson disease 2 (PARK2 / PARK-PRKN) is an
  early-onset parkinsonian disorder caused by biallelic loss-of-function
  variants in PRKN, which encodes the RING-between-RING E3 ubiquitin ligase
  parkin. Parkin is the downstream effector of the PINK1-parkin mitochondrial
  quality-control axis: mitochondrial depolarization stabilizes PINK1 on the
  outer mitochondrial membrane, PINK1 phosphorylates ubiquitin at Ser65 to
  recruit and allosterically activate parkin, and parkin then ubiquitinates
  outer-membrane substrates to mark the damaged organelle for autophagic
  clearance (mitophagy). Biallelic parkin loss disables this arm, allowing
  damaged mitochondria, oxidative damage, and released mitochondrial DNA to
  accumulate, with selective degeneration of substantia nigra pars compacta
  dopaminergic neurons and consequent nigrostriatal dopamine deficiency.
  Clinically the disorder is distinguished from common late-onset Parkinson
  disease by its early median onset (~31 years), frequent lower-limb dystonia
  at presentation, hyperreflexia, an excellent and sustained levodopa response
  complicated by early levodopa-induced dyskinesias, slow progression, and
  cognitive decline no more frequent than in the general population.
  Neuropathologically it is characterized by severe but topographically
  restricted (predominantly ventral) nigral neuronal loss that is usually
  Lewy-body negative, a genuine point of divergence from idiopathic Parkinson
  disease.
category: Mendelian
parents:
- Neurodegenerative Disease
- Movement Disorder
disease_term:
  preferred_term: autosomal recessive juvenile Parkinson disease 2
  term:
    id: MONDO:0010820
    label: autosomal recessive juvenile Parkinson disease 2
synonyms:
- PARK2
- PARK-PRKN
- PRKN-related early-onset Parkinson disease
- autosomal recessive juvenile parkinsonism
- Parkinson disease 2, autosomal recessive juvenile
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
notes: >-
  Lump-vs-split rationale: this entry is deliberately kept SEPARATE from the
  existing `Parkinsons_Disease` entry (MONDO:0005180), which curates the
  common, largely sporadic, late-onset alpha-synucleinopathy. The two are
  complementary rather than redundant. (1) Different mechanism anchor: the
  dismech `Parkinsons_Disease` graph is built on misfolded alpha-synuclein
  aggregation and Lewy-body pathology, whereas PARK-PRKN is a monogenic
  mitochondrial-quality-control (PINK1-parkin mitophagy) disorder in which
  Lewy bodies are usually absent. (2) Different neuropathology: PARK-PRKN
  shows predominantly ventral-tier nigral loss with relative dorsal-tier
  preservation and absent or rare Lewy bodies (PMID:23459986). (3) Different
  clinical signature: early median onset, dystonia at presentation,
  hyperreflexia, excellent sustained levodopa response with early dyskinesias,
  and slow progression. (4) Different actionable genetics: the mutational
  spectrum is dominated by whole-exon deletions and duplications that
  sequencing-only panels miss, so dosage analysis (e.g. MLPA) is required.
  The existing `Parkinsons_Disease` entry already lists PRKN in its `genetic`
  section as one contributor to the broader PD gene landscape; that remains
  appropriate and is not duplicated here. ClinGen curates the PRKN
  gene-disease relationship at the broad "Parkinson disease" (MONDO:0005180)
  level rather than against MONDO:0010820, which is why the gene-validity
  evidence in this entry cites that broader assertion.
  Named-entity-confusion (NEC) preflight was performed before curation: the
  PARK numbered series is a high-NEC-risk class and PARK2/PRKN, PARK6/PINK1
  and PARK7/DJ-1 are frequently conflated in the literature. MONDO:0010820 was
  confirmed via OAK to carry `RO:0004003 HGNC:8607 ! PRKN`, `xref OMIM:600116`,
  and the synonyms "PARK2" and "PRKN young-onset Parkinson disease". All
  evidence in this entry was checked to be about PRKN/parkin rather than PINK1
  or DJ-1; where a cited study reports PRKN and PINK1 jointly (PMID:33029617,
  PMID:29644727) that joint scope is stated explicitly in the evidence
  explanation.
  Deep-research provenance: a `claude_code` deep-research run was performed
  (`research/PRKN-Related_Juvenile_Parkinson_Disease-deep-research-claude_code.md`
  plus its `.citations.md` sidecar; 13 web searches, 42 citations, 306 s).
  It was used as a completeness cross-check only - every claim in this entry is
  sourced to a `just fetch-reference`-cached primary reference that was read
  directly, not to the DR narrative. A gene-frequency NEC check on the report
  itself passed: PRKN/PARK2 is mentioned ~108 times versus PINK1 13 and DJ-1 2,
  confirming the report resolved to the intended entity rather than a PARK-series
  sibling.
  Retracted-literature note: PMID:30135585 (Sliter et al., Nature 2018,
  "Parkin and PINK1 mitigate STING-induced inflammation") is the most widely
  cited source for the parkin-STING innate-immune arm, but it was RETRACTED in
  2025 (Nature 644:1116). It is therefore deliberately NOT cited anywhere in
  this entry. The innate-immune arm is instead sourced to the independent
  human study PMID:33029617.
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    PARK-PRKN is inherited in an autosomal recessive manner; affected
    individuals carry biallelic (homozygous or compound heterozygous)
    pathogenic PRKN variants. Heterozygous carriers are generally unaffected,
    although heterozygosity has been proposed as a Parkinson disease risk
    factor.
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PARK-PRKN is inherited in an autosomal recessive manner."
    explanation: >-
      GeneReviews states the mode of inheritance directly, supporting the
      HP:0000007 binding.
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of PARK-PRKN is established in a proband with suggestive
      findings and biallelic pathogenic variants in PRKN identified by
      molecular genetic testing.
    explanation: >-
      Confirms that two pathogenic PRKN alleles are required, i.e. recessive
      rather than dominant gene action.
prevalence:
- population: Worldwide
  measure_type: UNKNOWN
  prevalence_class: RARE
  notes: >-
    No direct population-based prevalence estimate for PARK-PRKN specifically
    was identified in the sources used for this entry, so only the coarse
    qualitative band is asserted. The rarity can be bounded indirectly: only a
    small minority of Parkinson disease is early-onset, and only a minority of
    early-onset cases carry biallelic PRKN variants (see the structured
    `case_fractions` on the PRKN `genetic` entry, which is the well-quantified
    dimension). Do not read this record as a measured rate.
  evidence:
  - reference: PMID:22956510
    reference_title: "Systematic review and UK-based study of PARK2 (parkin), PINK1, PARK7 (DJ-1) and LRRK2 in early-onset Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Approximately 3.6% of patients with Parkinson's disease develop symptoms
      before age 45.
    explanation: >-
      Supports the rarity band only indirectly. It quantifies the early-onset
      Parkinson disease denominator, not the prevalence of PARK-PRKN itself;
      PRKN-attributable cases are a minority of that already small subgroup.
      Marked PARTIAL because the quoted statistic does not measure this
      disease's occurrence.
progression:
- phase: Age at onset
  notes: >-
    Median age at onset approximately 31 years, with a very wide reported range
    (1-84 years). Progression is slow and disease duration of more than 60
    years has been reported, in contrast to the more rapid course typical of
    late-onset Parkinson disease.
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The median age at onset is 31 years (range: 1-84 years)."
    explanation: GeneReviews gives the median and range of age at onset.
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The disease is slowly progressive: a disease duration of more than 60
      years has been reported.
    explanation: Supports the slow rate of progression and long disease duration.
  - reference: PMID:29644727
    reference_title: "Genotype-Phenotype Relations for the Parkinson's Disease Genes Parkin, PINK1, DJ1: MDSGene Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      median age at onset of ∼30 years for carriers of at least 2 mutations in
      any of the 3 genes
    explanation: >-
      Independent systematic-review confirmation of the early median onset.
      Note the MDSGene figure pools carriers of biallelic variants in Parkin,
      PINK1 or DJ1 rather than PRKN alone.
genetic:
- name: PRKN
  gene_term:
    preferred_term: PRKN
    term:
      id: hgnc:8607
      label: PRKN
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: present
  association: >-
    Biallelic loss-of-function variants in PRKN (formerly PARK2), encoding the
    RING-between-RING E3 ubiquitin ligase parkin, cause autosomal recessive
    juvenile/early-onset Parkinson disease. The gene lies at 6q25.2-q27, spans
    more than 500 kb, and has 12 exons.
  notes: >-
    MUTATIONAL SPECTRUM - CLINICALLY IMPORTANT: large intragenic copy-number
    changes (whole-exon deletions and duplications/multiplications) are a major
    component of the PRKN mutational spectrum, alongside point mutations, and
    the first pathogenic alleles ever described in this gene were exon
    deletions. This is consistent with the gene's very large genomic footprint
    (>500 kb across 12 exons). The practical consequence is that a
    sequencing-only panel or exome cannot detect this class of allele at all:
    exon-dosage analysis (MLPA or an equivalent copy-number method) is required
    to avoid false-negative genetic testing, and an apparently "single
    heterozygous point mutation" result should prompt dosage testing for a
    second, exonic rearrangement allele in trans. Deliberately NOT asserted
    here: the proportion of patients or alleles attributable to rearrangements
    versus point mutations. The cited sources report counts of DISTINCT variant
    types (19 rearrangements vs 16 point mutations in PMID:10824074), which is
    not the same quantity, and no source examined reports the allele-share
    split.
  evidence:
  - reference: PMID:9560156
    reference_title: "Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutations in the newly identified gene appear to be responsible for the
      pathogenesis of AR-JP, and we have therefore named the protein product
      'Parkin'.
    explanation: >-
      The original positional-cloning report establishing PRKN/parkin as the
      gene underlying autosomal recessive juvenile parkinsonism.
  - reference: PMID:9560156
    reference_title: "Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The gene spans more than 500 kilobases and has 12 exons, five of which
      (exons 3-7) are deleted in the patient. Four other AR-JP patients from
      three unrelated families have a deletion affecting exon 4 alone.
    explanation: >-
      Documents the gene structure and the founding observation that
      multi-exon and single-exon deletions - not point mutations - were the
      first pathogenic alleles identified, anchoring the CNV-dominant
      mutational spectrum.
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Nineteen different rearrangements of exons (deletions and
      multiplications) and 16 different point mutations were detected.
    explanation: >-
      Quantifies the DIVERSITY of the mutational spectrum in a large
      multicentre series: 19 distinct exonic rearrangements versus 16 distinct
      point mutations. Note this counts distinct variant types, NOT the share of
      alleles or patients attributable to each class - the abstract does not
      report that split - so the claim made here is only that exonic
      rearrangements are a large and irreducible part of the spectrum, which is
      why copy-number analysis is required for complete PRKN testing.
  - 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: >-
      The ClinGen Parkinson's Disease Gene Curation Expert Panel classifies the
      PRKN gene-disease relationship as Definitive with autosomal recessive
      inheritance. ClinGen curates this against the broad Parkinson disease
      concept (MONDO:0005180) rather than against MONDO:0010820.
  case_fractions:
  - population: >-
      Early-onset Parkinson disease, pooled systematic review of previously
      reported studies
    case_fraction_percent: 8.6
    cohort_size: 5800
    notes: >-
      Weighted mean proportion of early-onset Parkinson disease cases carrying
      PARK2/PRKN mutations across a systematic review of more than 5800 unique
      cases. The authors state only that the overall frequency was lower than
      previously estimated; they do not attribute that gap to any specific
      cause, so no explanation for it is asserted here.
    evidence:
    - reference: PMID:22956510
      reference_title: "Systematic review and UK-based study of PARK2 (parkin), PINK1, PARK7 (DJ-1) and LRRK2 in early-onset Parkinson's disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Our systematic review included information from >5800 unique cases.
        Overall, the weighted mean proportion of cases with PARK2 (parkin),
        PINK1, and PARK7 (DJ-1) mutations was 8.6%, 3.7%, and 0.4%,
        respectively.
      explanation: >-
        Directly quantifies the PARK2/PRKN share of early-onset Parkinson
        disease cases in a pooled systematic review.
  - population: >-
      European families with early-onset Parkinson disease (onset at or before
      age 45, unaffected parents)
    case_fraction_percent: 49.0
    cohort_size: 73
    notes: >-
      Family-ascertained cohort, so this fraction is substantially higher than
      the pooled systematic-review estimate; recessive inheritance is enriched
      by requiring an affected sib-ship with unaffected parents.
    evidence:
    - reference: PMID:10824074
      reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Among the families with early-onset Parkinson's disease, 36 (49
        percent) had parkin mutations.
      explanation: Direct case-fraction statistic for the familial EOPD cohort.
  - population: >-
      Isolated (non-familial) Parkinson disease with age at onset 20 years or
      younger
    case_fraction_percent: 77.0
    cohort_size: 13
    notes: >-
      The case fraction is strongly age-at-onset dependent: 77% at onset 20
      years or younger versus only 3% at onset over 30 years in the same study.
      Small denominator (13 patients) for the youngest stratum.
    evidence:
    - reference: PMID:10824074
      reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Among the patients with isolated Parkinson's disease, mutations were
        detected in 10 of 13 patients (77 percent) with an age at onset of 20
        years or younger, but in only 2 of 64 patients (3 percent) with an age
        at onset of more than 30 years.
      explanation: >-
        Quantifies the steep dependence of the PRKN case fraction on age at
        onset, with both the youngest and the older strata reported.
pathophysiology:
- name: PRKN Biallelic Loss of Function
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Homozygous or compound heterozygous loss-of-function PRKN alleles - most
    often whole-exon deletions or duplications, and less often point mutations
    - abolish functional parkin, an E3 ubiquitin ligase. This is the initiating
    molecular lesion of PARK-PRKN.
  gene:
    preferred_term: PRKN
    term:
      id: hgnc:8607
      label: PRKN
  molecular_functions:
  - preferred_term: parkin ubiquitin protein ligase activity
    term:
      id: GO:0061630
      label: ubiquitin protein ligase activity
    modifier: DECREASED
  evidence:
  - reference: PMID:9560156
    reference_title: "Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      encoding a protein of 465 amino acids with moderate similarity to
      ubiquitin at the amino terminus and a RING-finger motif at the carboxy
      terminus
    explanation: >-
      Identifies parkin as a RING-finger (E3 ubiquitin ligase family) protein
      disrupted by deletion in AR-JP patients.
  - reference: PMID:24784582
    reference_title: "Ubiquitin is phosphorylated by PINK1 to activate parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      PINK1 (PTEN induced putative kinase 1) and PARKIN (also known as PARK2)
      have been identified as the causal genes responsible for hereditary
      recessive early-onset Parkinsonism.
    explanation: >-
      Confirms PRKN/PARK2 as a causal gene for hereditary recessive
      early-onset parkinsonism and situates it in the PINK1-parkin axis.
  downstream:
  - target: Failure of Phospho-Ubiquitin-Dependent Parkin Recruitment and E3 Ligase Activation
    causal_link_type: DIRECT
    description: >-
      With no functional parkin protein, the recruitment/activation step of the
      PINK1-parkin axis cannot proceed regardless of an intact upstream PINK1
      signal.
    evidence:
    - reference: PMID:20126261
      reference_title: "PINK1 is selectively stabilized on impaired mitochondria to activate Parkin."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        disease-causing mutations in PINK1 and Parkin disrupt Parkin
        recruitment and Parkin-induced mitophagy at distinct steps
      explanation: >-
        Shows directly that disease-causing parkin mutations break the
        recruitment/mitophagy pathway.
- name: Mitochondrial Depolarization
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Loss of inner mitochondrial membrane potential marks an individual
    mitochondrion as damaged. This is the upstream damage state that the
    PINK1-parkin quality-control system detects; it is scale-MOLECULAR and is
    modelled separately from the PINK1 sensing response it triggers.
  biological_processes:
  - preferred_term: mitochondrial depolarization
    term:
      id: GO:0051882
      label: mitochondrial depolarization
  evidence:
  - reference: PMID:20126261
    reference_title: "PINK1 is selectively stabilized on impaired mitochondria to activate Parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Parkin is selectively recruited to damaged mitochondria that have lost
      their membrane potential
    explanation: >-
      Establishes loss of membrane potential as the damage state that the
      pathway acts on.
  downstream:
  - target: PINK1 Accumulation on the Outer Mitochondrial Membrane
    causal_link_type: DIRECT
    description: >-
      Depolarization blocks the voltage-dependent proteolysis that normally
      keeps outer-membrane PINK1 low, so PINK1 accumulates selectively on the
      depolarized organelle.
    evidence:
    - reference: PMID:20126261
      reference_title: "PINK1 is selectively stabilized on impaired mitochondria to activate Parkin."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        we show that expression of PINK1 on individual mitochondria is regulated
        by voltage-dependent proteolysis to maintain low levels of PINK1 on
        healthy, polarized mitochondria, while facilitating the rapid
        accumulation of PINK1 on mitochondria that sustain damage
      explanation: >-
        Directly demonstrates that membrane potential gates PINK1 abundance on
        the outer membrane.
- name: PINK1 Accumulation on the Outer Mitochondrial Membrane
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Full-length PINK1 accumulates on the outer membrane of the depolarized
    organelle with its kinase domain facing the cytosol. This is the
    damage-sensing step that flags an individual mitochondrion for disposal and
    is the immediate upstream requirement for parkin recruitment.
  biological_processes:
  - preferred_term: PINK1 kinase autophosphorylation and stabilization
    term:
      id: GO:0018105
      label: peptidyl-serine phosphorylation
  evidence:
  - reference: PMID:20126261
    reference_title: "PINK1 is selectively stabilized on impaired mitochondria to activate Parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Selective accumulation of PINK1 on the impaired mitochondria recruits
      Parkin, and Parkin, in turn, induces the degradation of the damaged
      mitochondria.
    explanation: >-
      States the sensing step and its immediate consequence for parkin
      recruitment.
  downstream:
  - target: Failure of Phospho-Ubiquitin-Dependent Parkin Recruitment and E3 Ligase Activation
    causal_link_type: DIRECT
    description: >-
      Accumulated PINK1 is necessary and sufficient to recruit parkin; in
      PARK-PRKN the PINK1 signal is generated normally but has no competent
      effector.
    evidence:
    - reference: PMID:20126261
      reference_title: "PINK1 is selectively stabilized on impaired mitochondria to activate Parkin."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        PINK1 accumulation on mitochondria is both necessary and sufficient for
        Parkin recruitment to mitochondria
      explanation: >-
        Defines the causal dependency of parkin recruitment on PINK1
        accumulation.
- name: Failure of Phospho-Ubiquitin-Dependent Parkin Recruitment and E3 Ligase Activation
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Mitochondrial PINK1 phosphorylates ubiquitin at Ser65. Phospho-ubiquitin is
    the genuine parkin activator: it binds parkin allosterically, unlocking the
    autoinhibited catalytic cysteine, while PINK1-dependent phosphorylation of
    parkin itself completes full activation. In PARK-PRKN this convergence step
    fails because parkin is absent or catalytically dead, so the Ser65
    phospho-ubiquitin signal is generated but not transduced.
  molecular_functions:
  - preferred_term: parkin E3 ubiquitin ligase activation
    term:
      id: GO:0061630
      label: ubiquitin protein ligase activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: PINK1-mediated ubiquitin Ser65 phosphorylation
    term:
      id: GO:0018105
      label: peptidyl-serine phosphorylation
  evidence:
  - reference: PMID:24784582
    reference_title: "Ubiquitin is phosphorylated by PINK1 to activate parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Here we report that ubiquitin is the genuine substrate of PINK1. PINK1
      phosphorylated ubiquitin at Ser 65 both in vitro and in cells
    explanation: >-
      Identifies ubiquitin Ser65 as the PINK1 substrate that constitutes the
      activating signal.
  - reference: PMID:24784582
    reference_title: "Ubiquitin is phosphorylated by PINK1 to activate parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The phosphorylation-dependent interaction between ubiquitin and parkin
      suggests that phosphorylated ubiquitin unlocks autoinhibition of the
      catalytic cysteine.
    explanation: >-
      Provides the allosteric mechanism by which phospho-ubiquitin activates
      parkin's latent E3 activity.
  - reference: PMID:24784582
    reference_title: "Ubiquitin is phosphorylated by PINK1 to activate parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      PINK1 acts as an upstream factor for parkin and is essential both for the
      activation of latent E3 parkin activity and for recruiting parkin onto
      depolarized mitochondria.
    explanation: >-
      States the epistatic ordering (PINK1 upstream of parkin) and the dual
      recruitment/activation role.
  downstream:
  - target: Loss of Ubiquitination of Outer Mitochondrial Membrane Substrates
    causal_link_type: DIRECT
    description: >-
      Activated parkin is the enzyme that transfers ubiquitin onto
      outer-membrane proteins; without activation this transfer does not occur.
    evidence:
    - reference: PMID:24784582
      reference_title: "Ubiquitin is phosphorylated by PINK1 to activate parkin."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        parkin is an E3 ubiquitin ligase that catalyses ubiquitin transfer to
        mitochondrial substrates
      explanation: >-
        Establishes the enzymatic step that is lost downstream of failed parkin
        activation.
- name: Loss of Ubiquitination of Outer Mitochondrial Membrane Substrates
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Activated parkin decorates outer mitochondrial membrane proteins with
    ubiquitin chains, which are further phosphorylated by PINK1 to generate a
    feed-forward amplification loop and to build the autophagy-receptor
    recognition signal on the damaged organelle. In PARK-PRKN this ubiquitin
    coat is not deposited, so the damaged mitochondrion is never tagged for
    disposal.
  biological_processes:
  - preferred_term: ubiquitination of outer mitochondrial membrane substrates
    term:
      id: GO:0016567
      label: protein ubiquitination
    modifier: DECREASED
  evidence:
  - reference: PMID:24784582
    reference_title: "Ubiquitin is phosphorylated by PINK1 to activate parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our results show that PINK1-dependent phosphorylation of both parkin and
      ubiquitin is sufficient for full activation of parkin E3 activity.
    explanation: >-
      Supports that parkin E3 activity - and hence substrate ubiquitination -
      is the output of this module and is lost when parkin is absent.
  downstream:
  - target: Impaired Mitophagy
    causal_link_type: DIRECT
    description: >-
      The parkin-deposited ubiquitin signal is what commits the damaged
      mitochondrion to autophagic engulfment; its absence blocks mitophagy.
    evidence:
    - reference: PMID:20126261
      reference_title: "PINK1 is selectively stabilized on impaired mitochondria to activate Parkin."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Parkin is selectively recruited from the cytosol to damaged
        mitochondria to trigger their autophagy.
      explanation: >-
        Links parkin action on damaged mitochondria directly to their
        autophagic degradation.
- name: Impaired Mitophagy
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Mitophagy - the selective autophagic elimination of damaged mitochondria -
    is the terminal output of the PINK1-parkin axis and constitutes a
    mitochondrial quality-control system. Loss of parkin disables the
    parkin-dependent arm of this system, so damaged organelles are neither
    tagged nor cleared. Post-mitotic dopaminergic neurons, which cannot dilute
    damaged mitochondria by division, are predicted to be particularly reliant
    on this pathway.
  biological_processes:
  - preferred_term: mitophagy
    term:
      id: GO:0000422
      label: autophagy of mitochondrion
    modifier: DECREASED
  cell_types:
  - preferred_term: dopaminergic neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  evidence:
  - reference: PMID:20126261
    reference_title: "PINK1 is selectively stabilized on impaired mitochondria to activate Parkin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      they support a novel model for the negative selection of damaged
      mitochondria, in which PINK1 signals mitochondrial dysfunction to Parkin,
      and Parkin promotes their elimination
    explanation: >-
      States the quality-control model whose parkin-dependent arm is lost in
      PARK-PRKN.
  - reference: PMID:33029617
    reference_title: "Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Recent research in murine models suggests that parkin and PINK1 deficiency
      leads to impaired mitophagy, which causes the release of mitochondrial DNA
      (mtDNA), thereby triggering inflammation.
    explanation: >-
      Frames impaired mitophagy as the consequence of parkin deficiency and
      links it forward to the mtDNA-release arm. Tagged MODEL_ORGANISM and
      quoted with its full "Recent research in murine models suggests that"
      lead-in, because this sentence is the authors' summary of mouse work
      rather than their own human cohort result. The source also treats PRKN and
      PINK1 deficiency jointly.
  downstream:
  - target: Accumulation of Damaged Mitochondria
    causal_link_type: DIRECT
    description: >-
      Undisposed damaged mitochondria persist, with falling respiratory-chain
      capacity and rising reactive oxygen species and oxidative damage.
    evidence:
    - reference: PMID:14985362
      reference_title: "Mitochondrial dysfunction and oxidative damage in parkin-deficient mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The combination of proteomic, genetic, and physiological analyses reveal
        an essential role for parkin in the regulation of mitochondrial function
      explanation: >-
        In vivo demonstration in parkin-null mice that loss of parkin degrades
        mitochondrial function.
- name: Accumulation of Damaged Mitochondria
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Without parkin-dependent clearance, dysfunctional mitochondria are not
    removed from the network and accumulate in the cell. This is the direct
    organelle-level consequence of the mitophagy block, modelled separately
    from the oxidative/bioenergetic damage it subsequently produces.
  biological_processes:
  - preferred_term: mitochondrion organization
    term:
      id: GO:0007005
      label: mitochondrion organization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:14985362
    reference_title: "Mitochondrial dysfunction and oxidative damage in parkin-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The combination of proteomic, genetic, and physiological analyses reveal
      an essential role for parkin in the regulation of mitochondrial function
    explanation: >-
      Establishes that loss of parkin degrades the mitochondrial population in
      vivo.
  downstream:
  - target: Oxidative Stress and Respiratory Chain Deficiency
    causal_link_type: DIRECT
    description: >-
      Retained dysfunctional mitochondria have reduced respiratory-chain
      capacity and generate oxidative damage.
    evidence:
    - reference: PMID:14985362
      reference_title: "Mitochondrial dysfunction and oxidative damage in parkin-deficient mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Consistent with reductions in several subunits of complexes I and IV,
        functional assays showed reductions in respiratory capacity of striatal
        mitochondria isolated from parkin-/- mice.
      explanation: >-
        Direct in vivo measurement of respiratory-chain impairment caused by
        parkin loss.
  - target: Cytosolic and Circulating mtDNA Release
    causal_link_type: DIRECT
    description: >-
      Damaged, uncleared mitochondria release mitochondrial DNA, which acts as
      a damage-associated molecular pattern.
    evidence:
    - reference: PMID:33029617
      reference_title: "Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        increased circulating cell-free mtDNA serum levels in both patients with
        biallelic or with heterozygous PRKN/PINK1 mutations compared to
        idiopathic Parkinson's disease
      explanation: >-
        Human evidence that PRKN mutation carriers have elevated circulating
        cell-free mtDNA, consistent with release from uncleared damaged
        mitochondria.
- name: Oxidative Stress and Respiratory Chain Deficiency
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    In parkin-null mice the retained dysfunctional mitochondria manifest as
    reduced abundance of complex I and complex IV subunits, measurably reduced
    respiratory capacity of striatal mitochondria, reduced antioxidant
    defences, and increased protein and lipid peroxidation. Chronic oxidative
    burden is the proposed proximate injury to dopaminergic neurons.
  biological_processes:
  - preferred_term: oxidative stress response
    term:
      id: GO:0006979
      label: response to oxidative stress
    modifier: ABNORMAL
  locations:
  - preferred_term: striatum
    term:
      id: UBERON:0002435
      label: striatum
  evidence:
  - reference: PMID:14985362
    reference_title: "Mitochondrial dysfunction and oxidative damage in parkin-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      parkin-/- mice showed decreased serum antioxidant capacity and increased
      protein and lipid peroxidation
    explanation: >-
      Demonstrates the oxidative-damage arm downstream of parkin loss in vivo.
  downstream:
  - target: Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Chronic mitochondrial dysfunction and oxidative damage are the proposed
      cell-autonomous driver of nigral dopaminergic degeneration. The link is
      marked INDIRECT_UNKNOWN_INTERMEDIATES deliberately: parkin-null mice show
      the mitochondrial and oxidative phenotype WITHOUT nigral neuron loss, so
      the intermediate steps that convert this cellular stress into human
      dopaminergic cell death are not established (see the HUMAN_MODEL_MISMATCH
      discussion on this entry).
    evidence:
    - reference: PMID:14985362
      reference_title: "Mitochondrial dysfunction and oxidative damage in parkin-deficient mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        provide the first direct evidence of mitochondrial dysfunction and
        oxidative damage in the absence of nigral degeneration in a genetic
        mouse model of Parkinson's disease
      explanation: >-
        Marked PARTIAL because the same study that establishes the mitochondrial
        and oxidative phenotype explicitly reports it occurring WITHOUT nigral
        degeneration in mice, so it supports the upstream half of the edge while
        arguing against a simple sufficiency claim.
- name: Cytosolic and Circulating mtDNA Release
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Mitochondrial DNA escapes from uncleared damaged mitochondria. In humans
    this is measurable as increased circulating cell-free mtDNA in carriers of
    biallelic or heterozygous PRKN/PINK1 mutations relative to idiopathic
    Parkinson disease, whereas unaffected heterozygous carriers have
    control-level concentrations. Released mtDNA is the damage-associated
    molecular pattern that the downstream innate immune sensor detects.
  evidence:
  - reference: PMID:33029617
    reference_title: "Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      By contrast, circulating cell-free mtDNA concentrations in unaffected
      heterozygous carriers of PRKN/PINK1 mutations were comparable to control
      levels
    explanation: >-
      The authors' own human cohort measurement, showing mtDNA release tracks
      affected status rather than carrier status alone.
  downstream:
  - target: cGAS-STING Innate Immune Activation
    causal_link_type: DIRECT
    description: >-
      Cytosolic mtDNA is sensed by cGAS-STING, converting the organelle defect
      into an inflammatory signal.
    evidence:
    - reference: PMID:33029617
      reference_title: "Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        the CGAS (cyclic GMP-AMP synthase)-STING (stimulator of interferon
        genes) pathway mitigates activation of the innate immune system,
        quantifiable as increased interleukin-6 (IL6) levels
      explanation: >-
        Names the cGAS-STING sensing route. Tagged MODEL_ORGANISM because this
        sentence is the authors' introductory summary of murine work ("Recent
        research in murine models suggests that..."), not their own human
        result.
- name: cGAS-STING Innate Immune Activation
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  description: >-
    Sensing of released mtDNA drives type I interferon and interleukin-6
    responses. In humans, patients with biallelic PRKN/PINK1 mutations have
    elevated serum IL-6 relative to healthy controls, with an apparent
    gene-dosage effect between biallelic and heterozygous carriers, and IL-6
    correlates with disease duration in mutation carriers but not in idiopathic
    Parkinson disease. Marked PROVISIONAL: the human data are serum biomarker
    associations rather than demonstrations of causal neuroinflammatory
    neurodegeneration.
  biological_processes:
  - preferred_term: interleukin-6 production
    term:
      id: GO:0032755
      label: positive regulation of interleukin-6 production
    modifier: INCREASED
  - preferred_term: type I interferon production
    term:
      id: GO:0032606
      label: type I interferon production
    modifier: INCREASED
  notes: >-
    The most widely cited mouse source for the parkin-STING arm (Sliter et al.,
    Nature 2018) was retracted in 2025 and is deliberately not cited here. The
    human-facing claims on this node therefore rest on independent human
    biomarker data, and the one mechanistic sentence borrowed from the murine
    literature is tagged MODEL_ORGANISM rather than presented as human evidence.
  evidence:
  - reference: PMID:33029617
    reference_title: "Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      elevated IL6 levels in patients with biallelic PRKN/PINK1 mutations
      compared to healthy control subjects in a German cohort, supporting the
      concept of a role for inflammation in PRKN/PINK1-linked Parkinson's
      disease
    explanation: >-
      The authors' own human cohort result: an inflammatory arm specifically in
      biallelic PRKN/PINK1 patients, validated in a second Italian cohort.
  - reference: PMID:33029617
    reference_title: "Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a correlation between IL6 levels and disease duration in carriers of
      PRKN/PINK1 mutations, while no such association was observed for
      idiopathic Parkinson's disease patients
    explanation: >-
      Human cohort result distinguishing the PRKN/PINK1 inflammatory signature
      from idiopathic Parkinson disease.
  downstream:
  - target: Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Chronic mtDNA-driven innate immune activation is hypothesized to
      contribute to dopaminergic neurodegeneration. This edge is the least
      established in the graph - the supporting human data are peripheral serum
      biomarkers, not CNS neuropathology.
    evidence:
    - reference: PMID:33029617
      reference_title: "Mitochondrial damage-associated inflammation highlights biomarkers in PRKN/PINK1 parkinsonism."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        our study further implicates inflammation due to impaired mitophagy and
        subsequent mtDNA release in the pathogenesis of PRKN/PINK1-linked
        Parkinson's disease
      explanation: >-
        Marked PARTIAL: the authors implicate inflammation in pathogenesis but
        the measurements are peripheral serum IL-6 and cell-free mtDNA, so a
        causal contribution to nigral neuron death is inferred, not shown.
- name: Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Dopaminergic neurons of the substantia nigra pars compacta degenerate. In
    autopsy-confirmed parkin disease the magnitude of nigral neuronal loss is
    as severe as in idiopathic Parkinson disease, but the topography differs:
    loss is predominantly ventral with relative preservation of the dorsal
    tier. Mild neuronal loss also occurs in the locus coeruleus and dorsal motor
    nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe
    nucleus, or other brain regions - a markedly more restricted distribution
    than in idiopathic Parkinson disease.
  cell_types:
  - preferred_term: nigral dopaminergic neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  locations:
  - preferred_term: substantia nigra pars compacta
    term:
      id: UBERON:0001965
      label: substantia nigra pars compacta
  biological_processes:
  - preferred_term: dopaminergic neuron apoptosis
    term:
      id: GO:0051402
      label: neuron apoptotic process
    modifier: INCREASED
  evidence:
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neuronal counts in the substantia nigra pars compacta revealed that
      neuronal loss in the parkin cases was as severe as that seen in PD, but
      relative preservation of the dorsal tier was seen in comparison with PD
    explanation: >-
      Quantitative human neuropathology establishing both the severity and the
      distinctive ventral-predominant topography of nigral loss.
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mild neuronal loss was identified in the locus coeruleus and dorsal motor
      nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe
      nucleus, or other brain regions.
    explanation: >-
      Documents the restricted extranigral distribution that distinguishes
      parkin disease from idiopathic Parkinson disease.
  downstream:
  - target: Nigrostriatal Dopamine Deficiency
    causal_link_type: DIRECT
    description: >-
      Loss of nigral dopaminergic neurons removes the dopaminergic projection to
      the striatum, producing measurable presynaptic striatal dopaminergic
      denervation.
    evidence:
    - reference: PMID:10994015
      reference_title: "[18 F]-dopa PET study in patients with juvenile-onset PD and parkin gene mutations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        representing 28% of putamen and 44% of caudate nucleus control subject
        values
      explanation: >-
        In vivo human imaging quantifying the striatal presynaptic dopaminergic
        deficit in parkin-mutation patients.
- name: Nigrostriatal Dopamine Deficiency
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >-
    Degeneration of the nigrostriatal projection produces severe striatal
    dopamine deficiency, quantified in parkin-mutation patients by 18F-dopa PET
    as roughly 28% of control putaminal and 44% of control caudate uptake. This
    deficiency is the direct target of dopamine-replacement therapy and explains
    the excellent levodopa responsiveness of the disorder.
  biological_processes:
  - preferred_term: dopaminergic synaptic transmission
    term:
      id: GO:0001963
      label: synaptic transmission, dopaminergic
    modifier: DECREASED
  locations:
  - preferred_term: striatum
    term:
      id: UBERON:0002435
      label: striatum
  evidence:
  - reference: PMID:10994015
    reference_title: "[18 F]-dopa PET study in patients with juvenile-onset PD and parkin gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Parkin gene mutations cause a form of early-onset autosomal recessive PD
      with neuronal loss in the substantia nigra and no Lewy bodies.
    explanation: >-
      Confirms both the nigral degeneration underlying the dopamine deficit and
      the Lewy-body-negative pathology in the same imaged patient group.
  downstream:
  - target: Parkinsonism
    causal_link_type: DIRECT
    description: >-
      Striatal dopamine deficiency produces the cardinal motor syndrome of
      bradykinesia, rest tremor and rigidity.
    evidence:
    - reference: PMID:20301651
      reference_title: "PRKN-Related Early-Onset Parkinson Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        PRKN-related early-onset Parkinson disease (PARK-PRKN) is characterized
        by the cardinal signs of Parkinson disease (PD): bradykinesia, resting
        tremor, and rigidity.
      explanation: >-
        Establishes the clinical output of the nigrostriatal deficit.
- name: Parkinsonism
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    The clinical syndrome: bradykinesia with resting tremor and rigidity,
    typically with early lower-limb dystonia, hyperreflexia, symmetric
    involvement, an excellent and sustained levodopa response, and early
    levodopa-induced dyskinesias. Progression is slow and cognitive decline is
    no more frequent than in the general population.
  evidence:
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      they were more likely to have symmetric involvement and dystonia at onset,
      to have hyperreflexia at onset or later, to have a good response to
      levodopa therapy, and to have levodopa-induced dyskinesias during
      treatment
    explanation: >-
      Defines the distinguishing clinical signature of parkin-mutation patients
      relative to mutation-negative early-onset Parkinson disease.
phenotypes:
- category: Motor
  name: Bradykinesia
  description: >-
    Slowness of voluntary movement; one of the three cardinal signs of
    PARK-PRKN.
  phenotype_term:
    preferred_term: Bradykinesia
    term:
      id: HP:0002067
      label: Bradykinesia
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PRKN-related early-onset Parkinson disease (PARK-PRKN) is characterized
      by the cardinal signs of Parkinson disease (PD): bradykinesia, resting
      tremor, and rigidity.
    explanation: >-
      GeneReviews lists bradykinesia as a cardinal sign. No frequency band is
      asserted because this is a definitional statement, not a measured
      proportion.
- category: Motor
  name: Resting Tremor
  description: >-
    Tremor present at rest; a cardinal sign and, together with dystonia, a
    common presenting feature in autopsy-confirmed parkin disease.
  phenotype_term:
    preferred_term: Resting tremor
    term:
      id: HP:0002322
      label: Resting tremor
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PRKN-related early-onset Parkinson disease (PARK-PRKN) is characterized
      by the cardinal signs of Parkinson disease (PD): bradykinesia, resting
      tremor, and rigidity.
    explanation: GeneReviews lists resting tremor as a cardinal sign.
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Presenting signs in the parkin disease cases were hand or leg tremor often
      combined with dystonia.
    explanation: >-
      Autopsy-confirmed series describing tremor (with dystonia) as the typical
      presenting sign.
- category: Motor
  name: Rigidity
  description: Increased muscle tone; a cardinal sign of PARK-PRKN.
  phenotype_term:
    preferred_term: Rigidity
    term:
      id: HP:0002063
      label: Rigidity
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PRKN-related early-onset Parkinson disease (PARK-PRKN) is characterized
      by the cardinal signs of Parkinson disease (PD): bradykinesia, resting
      tremor, and rigidity.
    explanation: GeneReviews lists rigidity as a cardinal sign.
- category: Motor
  name: Lower-Limb Dystonia at Onset
  description: >-
    Dystonia, characteristically of the lower limb, is a hallmark presenting
    feature of PARK-PRKN and is one of the clinical clues that distinguishes it
    from mutation-negative early-onset Parkinson disease. It may antedate overt
    parkinsonism.
  phenotype_term:
    preferred_term: Leg dystonia
    term:
      id: HP:0031959
      label: Leg dystonia
  diagnostic: true
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lower-limb dystonia may be a presenting sign"
    explanation: >-
      GeneReviews identifies lower-limb dystonia as a presenting sign. No
      frequency band is asserted: "may be" does not map to a FrequencyEnum
      value.
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      they were more likely to have symmetric involvement and dystonia at onset
    explanation: >-
      Comparative evidence that dystonia at onset discriminates parkin-mutation
      carriers from non-carriers with early-onset Parkinson disease.
- category: Neurologic
  name: Hyperreflexia
  description: >-
    Brisk deep-tendon reflexes, an atypical finding for idiopathic Parkinson
    disease and a recognized clinical clue to PARK-PRKN. It may be present at
    onset or develop later.
  phenotype_term:
    preferred_term: Hyperreflexia
    term:
      id: HP:0001347
      label: Hyperreflexia
  frequency: FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical findings vary; hyperreflexia is common."
    explanation: >-
      Supports both the association and the FREQUENT band. The GeneReviews term
      "common" maps to FREQUENT (30-79%) under the project's
      literature-term-to-enum mapping table.
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "to have hyperreflexia at onset or later"
    explanation: >-
      Independent confirmation that hyperreflexia is over-represented in
      parkin-mutation carriers.
- category: Treatment Response
  name: Excellent and Sustained Levodopa Response
  description: >-
    PARK-PRKN characteristically shows an excellent and durable response to
    levodopa, often at relatively low doses. This is a defining therapeutic
    feature of the disorder and contrasts with the waning response seen in some
    other early-onset parkinsonian syndromes.
  phenotype_term:
    preferred_term: Parkinsonism with favorable response to dopaminergic medication
    term:
      id: HP:0002548
      label: Parkinsonism with favorable response to dopaminergic medication
  diagnostic: true
  evidence:
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "to have a good response to levodopa therapy"
    explanation: >-
      Parkin-mutation carriers were significantly more likely than non-carriers
      to have a good levodopa response.
  - reference: PMID:29644727
    reference_title: "Genotype-Phenotype Relations for the Parkinson's Disease Genes Parkin, PINK1, DJ1: MDSGene Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      an overall clinically typical form of PD with excellent treatment
      response, dystonia and dyskinesia being relatively common and cognitive
      decline relatively uncommon
    explanation: >-
      Systematic review of more than 1100 patients confirming the excellent
      treatment response. Note the review pools Parkin, PINK1 and DJ1.
- category: Treatment Response
  name: Levodopa-Induced Dyskinesia
  description: >-
    Dyskinesias complicating levodopa therapy occur frequently and often early
    in the disease course, which is why GeneReviews explicitly lists exceeding
    the levodopa dose needed for satisfactory clinical response as a
    circumstance to avoid.
  phenotype_term:
    preferred_term: Dyskinesia
    term:
      id: HP:0100660
      label: Dyskinesia
  frequency: FREQUENT
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dyskinesia as a result of treatment with levodopa frequently occurs.
    explanation: >-
      Supports both the association and the FREQUENT band; "frequently occurs"
      maps to FREQUENT (30-79%) under the project's mapping table.
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "to have levodopa-induced dyskinesias during treatment"
    explanation: >-
      Confirms the over-representation of levodopa-induced dyskinesias in
      parkin-mutation carriers.
- category: Motor
  name: Freezing of Gait
  description: >-
    Freezing of gait, postural deformity and motor fluctuations are common late
    features of parkin disease.
  phenotype_term:
    preferred_term: Freezing of gait
    term:
      id: HP:0031825
      label: Freezing of gait
  evidence:
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Freezing of gait, postural deformity, and motor fluctuations were common
      late features.
    explanation: >-
      Autopsy-confirmed parkin disease series describing late motor features.
      Frequency band omitted: "common late features" in a five-case series does
      not support a quantitative band.
- category: Cognitive
  name: Relative Cognitive Sparing
  description: >-
    In contrast to idiopathic Parkinson disease, where dementia is a common
    late outcome, cognitive decline in PARK-PRKN appears no more frequent than
    in the general population, and an autopsy-confirmed series found no
    cognitive impairment or dementia in any case. This relative cognitive
    sparing is a genuine point of clinical divergence and is consistent with
    the restricted neuropathology (no involvement of the nucleus basalis of
    Meynert). The substantive curated claim here is the ABSENCE of dementia,
    not a positive phenotype.
  phenotype_term:
    preferred_term: Cognition relatively preserved (no HPO term; NTR candidate)
  notes: >-
    NEEDS-TERM-REQUEST (NTR). This entry deliberately carries NO `term:` binding.
    HPO has no positive term for "cognition preserved", and both available
    workarounds are wrong: binding an HP dementia term would be read by
    downstream tooling as the disease HAVING dementia (the opposite of the
    curated finding, since dismech's phenotype model has no negation slot), and
    binding the general parent HP:0001300 Parkinsonism - which this entry did
    until PR review - is misleading because it labels a cognitive observation
    with a motor term that is already asserted elsewhere in the entry. An
    unbound `preferred_term` is the honest representation: the substantive claim
    is carried by the description and the two evidence items. An HPO term
    request for a "cognitive function preserved / not more frequent than
    population baseline" concept would be needed to bind this properly.
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      cognitive decline appears to be no more frequent than in the general
      population
    explanation: >-
      GeneReviews states that cognitive decline is not over-represented,
      supporting relative cognitive sparing.
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No patients had any evidence of cognitive impairment or dementia."
    explanation: >-
      Autopsy-confirmed series with no cognitive impairment in any of five
      cases.
histopathology:
- name: Lewy-Body-Negative Nigral Degeneration
  description: >-
    The distinguishing neuropathology of PARK-PRKN. Severe neuronal loss in the
    substantia nigra pars compacta occurs in the ABSENCE of the alpha-synuclein
    Lewy-body pathology that defines idiopathic Parkinson disease. Where Lewy
    bodies have been found in autopsy-confirmed parkin cases they were sparse
    and present in a minority of cases. The loss is topographically restricted
    - predominantly ventral tier, with relative dorsal-tier preservation, and
    limited extranigral involvement. This makes parkin disease a
    clinicopathologically distinct entity rather than simply an early-onset
    variant of idiopathic Parkinson disease, and is the single strongest
    argument for curating it as a separate dismech entry.
  finding_term:
    preferred_term: Lewy-body-negative nigral neuronal degeneration
    term:
      id: NCIT:C50774
      label: Tissue Degeneration
  diagnostic: true
  notes: >-
    The finding_term is bound to the generic NCIT morphologic finding "Tissue
    Degeneration" because neither NCIT nor the allowed HP branch provides a
    histopathology-result term for nigral neuronal loss or for absence of Lewy
    bodies. The specific finding is carried by `preferred_term`, the
    description, and the evidence.
  evidence:
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These findings support the notion that parkin disease is characterized by
      a more restricted morphologic abnormality than is found in PD, with
      predominantly ventral nigral degeneration and absent or rare Lewy bodies.
    explanation: >-
      The definitive statement of the distinguishing neuropathology from a
      controlled autopsy series (5 parkin cases vs 5 pathologically confirmed
      PD cases and 4 controls).
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sparse Lewy bodies were identified in 2 cases (brainstem and cortex).
    explanation: >-
      Marked PARTIAL because it qualifies the claim: Lewy bodies are usually
      but not invariably absent - 2 of 5 cases had sparse Lewy bodies. Curated
      explicitly so the entry does not overstate "Lewy-body negative" as
      absolute.
  - reference: PMID:10994015
    reference_title: "[18 F]-dopa PET study in patients with juvenile-onset PD and parkin gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Parkin gene mutations cause a form of early-onset autosomal recessive PD
      with neuronal loss in the substantia nigra and no Lewy bodies.
    explanation: >-
      Independent statement of the nigral-loss-without-Lewy-bodies pathology.
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The few available detailed neuropathologic reports suggest that homozygous
      and compound heterozygous parkin mutations are characterized by severe
      substantia nigra pars compacta neuronal loss.
    explanation: >-
      Establishes the severity of nigral loss in biallelic parkin mutation
      carriers.
imaging_findings:
- name: Reduced Striatal 18F-Dopa Uptake
  description: >-
    18F-dopa PET in juvenile-onset patients with parkin mutations shows a
    profound presynaptic dopaminergic deficit, with uptake reduced to
    approximately 28% of control values in the putamen and 44% in the caudate
    nucleus - a putamen-predominant gradient similar to idiopathic Parkinson
    disease.
  evidence:
  - reference: PMID:10994015
    reference_title: "[18 F]-dopa PET study in patients with juvenile-onset PD and parkin gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      representing 28% of putamen and 44% of caudate nucleus control subject
      values
    explanation: >-
      Quantifies the imaging phenotype. Based on three cases (one familial, two
      sporadic), so the point estimates should be read as illustrative.
  - reference: PMID:10994015
    reference_title: "[18 F]-dopa PET study in patients with juvenile-onset PD and parkin gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PD caused by parkin gene mutations is distinct from idiopathic PD on
      molecular grounds but has similar clinical and PET findings.
    explanation: >-
      Important nuance: imaging does NOT distinguish parkin disease from
      idiopathic Parkinson disease - the divergence is molecular and
      neuropathologic.
diagnosis:
- name: PRKN Molecular Genetic Testing with Exon-Dosage Analysis
  description: >-
    Diagnosis is established by identifying biallelic pathogenic PRKN variants.
    Because exonic deletions and duplications dominate the mutational spectrum,
    sequence analysis alone is insufficient and must be paired with a
    copy-number/dosage method (e.g. MLPA). A single heterozygous point mutation
    should prompt dosage testing for a second, rearrangement allele in trans.
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of PARK-PRKN is established in a proband with suggestive
      findings and biallelic pathogenic variants in PRKN identified by
      molecular genetic testing.
    explanation: States the diagnostic standard.
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All subjects were screened for mutations in the parkin gene with use of a
      semiquantitative polymerase-chain-reaction assay that simultaneously
      amplified several exons.
    explanation: >-
      Illustrates that a dosage-sensitive (semiquantitative, multi-exon) assay
      rather than plain sequencing was required to detect the rearrangements
      that made up the majority of alleles found.
  - reference: PMID:10824074
    reference_title: "Association between early-onset Parkinson's disease and mutations in the parkin gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Accurate diagnosis of these cases cannot be based only on the clinical
      manifestations of the disease.
    explanation: >-
      Supports the requirement for molecular confirmation rather than clinical
      diagnosis alone.
- name: Periodic Neurologic, Autonomic and Cognitive Surveillance
  description: >-
    Ongoing surveillance rather than one-off diagnosis. GeneReviews recommends
    neurologic examination together with assessment of autonomic function and
    cognitive issues every six to 12 months. The autonomic and cognitive
    components are the reason this is not simply motor follow-up: they are the
    domains that generate the non-motor management needs (constipation,
    genitourinary, sleep, orthostatic hypotension) curated under treatments.
  diagnosis_term:
    preferred_term: neurologic examination
    term:
      id: NCIT:C81313
      label: Neurologic Examination
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Surveillance: Neurologic examination and assessment of autonomic function
      and cognitive issues every six to 12 months.
    explanation: >-
      The GeneReviews Surveillance recommendation, including its six-to-12-month
      interval, quoted verbatim.
treatments:
- name: Levodopa/Carbidopa
  description: >-
    Dopamine replacement is the mainstay of therapy and PARK-PRKN responds
    excellently and durably, often at low doses. Carbidopa is a peripheral
    DOPA-decarboxylase inhibitor co-administered to reduce peripheral
    conversion. IMPORTANT SAFETY NOTE from the GeneReviews
    agents/circumstances-to-avoid section: levodopa dosing beyond what is needed
    for satisfactory clinical response should be avoided, because
    levodopa-induced dyskinesias occur frequently and early in this disorder.
  therapeutic_modality: SMALL_MOLECULE
  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: Nigrostriatal Dopamine Deficiency
    treatment_effect: RESTORES
    description: >-
      Levodopa is decarboxylated to dopamine in surviving nigrostriatal
      terminals and other striatal cells, replacing the missing neurotransmitter
      downstream of the degenerated neurons. It restores striatal dopaminergic
      neurotransmission without addressing the upstream mitophagy defect, which
      is why the response is symptomatic rather than disease-modifying.
    evidence:
    - reference: PMID:10994015
      reference_title: "[18 F]-dopa PET study in patients with juvenile-onset PD and parkin gene mutations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        representing 28% of putamen and 44% of caudate nucleus control subject
        values
      explanation: >-
        Quantifies the striatal dopaminergic deficit that dopamine replacement
        therapy compensates for.
  target_phenotypes:
  - preferred_term: Bradykinesia
    term:
      id: HP:0002067
      label: Bradykinesia
  - preferred_term: Rigidity
    term:
      id: HP:0002063
      label: Rigidity
  - preferred_term: Resting tremor
    term:
      id: HP:0002322
      label: Resting tremor
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment of manifestations: Levodopa and dopamine receptor agonists,
      monoamine oxidase type B inhibitors, catechol-O-methyltransferase
      inhibitors, amantadine, adenosine A2A receptor antagonists,
      anticholinergics
    explanation: GeneReviews management recommendation naming levodopa first-line.
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Agents/circumstances to avoid: Use of levodopa therapy that exceeds the
      dose needed for satisfactory clinical response.
    explanation: >-
      The GeneReviews drug-safety warning motivating dose restraint, given the
      frequent early levodopa-induced dyskinesias.
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dopamine-blocking therapies (both typical and atypical dopamine-blocking
      psychiatric medications as well as dopamine blockers for gastrointestinal
      causes) may exacerbate parkinsonism in individuals with PARK-PRKN and
      should be avoided, when possible.
    explanation: >-
      Second GeneReviews drug-safety warning: dopamine-blocking agents,
      including antiemetics, worsen parkinsonism and should be avoided.
- name: Deep Brain Stimulation
  description: >-
    Deep brain stimulation is recommended for individuals experiencing
    difficulty with levodopa therapy - in PARK-PRKN typically those limited by
    levodopa-induced dyskinesias and motor fluctuations rather than by loss of
    dopaminergic responsiveness.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: deep brain stimulation
    term:
      id: NCIT:C21024
      label: Deep Brain Stimulation
  target_phenotypes:
  - preferred_term: Dyskinesia
    term:
      id: HP:0100660
      label: Dyskinesia
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      deep brain stimulation for those experiencing difficulty with levodopa
      therapy
    explanation: GeneReviews management recommendation for DBS.
- name: Physical, Occupational and Speech Therapy
  description: >-
    Non-pharmacological rehabilitation: exercise as tolerated (aerobic,
    strength building and integrative), physical and occupational therapy, and
    speech and voice therapy. Particularly relevant here given the long disease
    duration and young age at onset.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      exercise as tolerated (aerobic, strength building, and integrative);
      physical and occupational therapy; speech and voice therapy
    explanation: GeneReviews management recommendations for rehabilitation.
- name: Non-Motor and Autonomic Symptom Management
  description: >-
    PARK-PRKN care is not confined to the motor syndrome. GeneReviews specifies
    symptomatic treatment of constipation; urology management of genitourinary
    manifestations; sleep aids, minimizing caffeine, good sleep hygiene and
    light therapy for sleep problems; and standard treatment of orthostatic
    hypotension. These matter disproportionately in this disorder because onset
    is early and disease duration can exceed 60 years, so the cumulative
    non-motor burden is carried for decades.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      symptomatic treatment of constipation; urology management of
      genitourinary manifestations; sleep aids, minimizing caffeine, good sleep
      hygiene, and light therapy for sleep problems; standard treatment of
      orthostatic hypotension
    explanation: >-
      The GeneReviews Management recommendations for the constipation,
      genitourinary, sleep and orthostatic-hypotension domains, quoted verbatim.
- name: Cognitive and Dementia Management
  description: >-
    Where cognitive impairment does occur, GeneReviews recommends cognitive
    behavioral therapy, pharmacologic treatment, and/or a cholinesterase
    inhibitor as needed. Note this is an "as needed" contingency rather than an
    expected course: cognitive decline in PARK-PRKN is no more frequent than in
    the general population (see the "Relative Cognitive Sparing" phenotype), in
    contrast to idiopathic Parkinson disease where dementia is a common late
    outcome.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: cholinesterase inhibitor
      term:
        id: NCIT:C47792
        label: Acetylcholinesterase Inhibitor
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      cognitive behavioral therapy, pharmacologic treatment, and/or
      cholinesterase inhibitor as needed for dementia
    explanation: >-
      The GeneReviews Management recommendation for cognitive/dementia care,
      quoted verbatim.
- name: Genetic Counseling
  description: >-
    Autosomal recessive recurrence counseling. Once the familial PRKN variants
    are known, heterozygote testing for at-risk relatives and prenatal or
    preimplantation genetic testing are possible.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      If both parents are known to be heterozygous for a PRKN pathogenic
      variant, each sib of an affected individual has at conception a 25% chance
      of being affected, a 50% chance of being heterozygous, and a 25% chance of
      inheriting neither of the familial PRKN pathogenic variants.
    explanation: GeneReviews recurrence-risk counseling content.
  - reference: PMID:20301651
    reference_title: "PRKN-Related Early-Onset Parkinson Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Once the PRKN pathogenic variants have been identified in an affected
      family member, heterozygote testing for at-risk relatives and
      prenatal/preimplantation genetic testing are possible.
    explanation: GeneReviews statement on cascade and reproductive testing.
differential_diagnoses:
- name: Idiopathic (late-onset) Parkinson Disease
  description: >-
    The principal differential. Distinguishing features favouring PARK-PRKN are
    early median onset (~31 years), lower-limb dystonia at presentation,
    hyperreflexia, symmetric involvement, slow progression, absence of cognitive
    decline, and Lewy-body-negative ventral-predominant nigral degeneration at
    autopsy. Critically, 18F-dopa PET does NOT separate the two entities.
    Curated separately in dismech as `Parkinsons_Disease` (MONDO:0005180).
  evidence:
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These findings support the notion that parkin disease is characterized by
      a more restricted morphologic abnormality than is found in PD, with
      predominantly ventral nigral degeneration and absent or rare Lewy bodies.
    explanation: >-
      Establishes parkin disease as pathologically distinct from idiopathic
      Parkinson disease.
  - reference: PMID:10994015
    reference_title: "[18 F]-dopa PET study in patients with juvenile-onset PD and parkin gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PD caused by parkin gene mutations is distinct from idiopathic PD on
      molecular grounds but has similar clinical and PET findings.
    explanation: >-
      Explicitly notes that PET imaging cannot make the distinction, so
      molecular testing is required.
- name: PINK1-related and DJ-1-related early-onset Parkinson disease
  description: >-
    PARK6 (PINK1) and PARK7 (DJ-1) are the other two autosomal recessive
    early-onset Parkinson disease genes and are clinically very similar,
    sharing early onset, excellent treatment response, dystonia and dyskinesia,
    and relative cognitive sparing. They cannot be reliably separated
    clinically and are frequently conflated in the literature (the PARK
    numbered series is a high named-entity-confusion risk class). PINK1 acts
    directly upstream of parkin in the same mitophagy pathway, which explains
    the phenotypic convergence. Molecular testing is the discriminator.
  evidence:
  - reference: PMID:29644727
    reference_title: "Genotype-Phenotype Relations for the Parkinson's Disease Genes Parkin, PINK1, DJ1: MDSGene Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This first comprehensive MDSGene review is devoted to the 3 autosomal
      recessive Parkinson's disease forms: PARK-Parkin, PARK-PINK1, and
      PARK-DJ1.
    explanation: >-
      Establishes the three-gene recessive differential that this entry must be
      distinguished from.
  - reference: PMID:22956510
    reference_title: "Systematic review and UK-based study of PARK2 (parkin), PINK1, PARK7 (DJ-1) and LRRK2 in early-onset Parkinson's disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PINK1 mutations were more common in Asian subjects.
    explanation: >-
      Documents ancestry-dependent differences in the relative contribution of
      the recessive EOPD genes, relevant to differential prioritization.
discussions:
- discussion_id: hmm_prkn_knockout_mouse_no_nigral_degeneration
  prompt: >-
    Why does germline parkin knockout in mice fail to reproduce the substantia
    nigra pars compacta dopaminergic neuron loss that is the defining
    neuropathology of human PARK-PRKN, and does this reflect species-specific
    compensation, insufficient lifespan/oxidative burden, or a genuinely
    different human disease mechanism?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Accumulation of Damaged Mitochondria
  - pathophysiology#Oxidative Stress and Respiratory Chain Deficiency
  - pathophysiology#Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta
  rationale: >-
    This is a textbook human-model mismatch and it sits precisely on the
    load-bearing edge of the pathograph. Parkin-null mice faithfully reproduce
    the UPSTREAM biology - impaired mitochondrial respiration, reduced complex
    I and IV subunits, reduced antioxidant capacity, increased protein and lipid
    peroxidation, altered striatal dopamine handling and nigrostriatal
    behavioural deficits - yet the number of dopaminergic neurons in the
    substantia nigra remains NORMAL up to 24 months of age. Human biallelic
    parkin carriers, by contrast, show nigral neuronal loss as severe as
    idiopathic Parkinson disease at autopsy. Evidence is therefore not absent
    (which would make this a KNOWLEDGE_GAP) but present-and-discordant: the
    mouse establishes the mitochondrial/oxidative arm while failing to
    translate it into the cell-death endpoint that defines the human disease.
    The mismatch has direct consequences for the knowledge base - it is why the
    edge from "Oxidative Stress and Respiratory Chain Deficiency" to
    "Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta"
    in this entry is typed INDIRECT_UNKNOWN_INTERMEDIATES rather than DIRECT -
    and for translation, since preclinical efficacy in this model cannot be read
    as protection against nigral degeneration. Candidate explanations include
    rodent lifespan being too short to accumulate the required oxidative/mtDNA
    burden, redundancy from other mitochondrial quality-control ligases, and
    species differences in nigral dopaminergic neuron vulnerability (pacemaking
    calcium load, neuromelanin, axonal arbor size).
  proposed_experiments:
  - experiment_id: exp_prkn_ipsc_nigral_neuron_survival
    name: >-
      Isogenic patient-derived iPSC nigral dopaminergic neuron survival under
      chronic mitochondrial stress
    description: >-
      Differentiate midbrain dopaminergic neurons from PRKN biallelic patient
      iPSCs and isogenic gene-corrected controls, apply chronic low-grade
      mitochondrial stress and extended culture, and measure mitophagic flux,
      mtDNA damage/release, cGAS-STING activation and neuron survival. This
      tests directly whether human nigral dopaminergic neurons, unlike mouse
      ones, convert the parkin-loss mitochondrial phenotype into cell death,
      and isolates whether the missing factor is cell-intrinsic species biology
      rather than duration of exposure.
  - experiment_id: exp_prkn_aged_stressed_model_nigral_counts
    name: >-
      Stereological nigral counts in aged and mitochondrially stressed
      parkin-null models
    description: >-
      Perform blinded stereological tyrosine-hydroxylase-positive nigral neuron
      counts in parkin-null animals aged to the limit of lifespan and/or
      sensitized with an independent mitochondrial-stress burden, in parallel
      with longitudinal pS65-ubiquitin and cell-free mtDNA measurements. A
      positive result would support the "insufficient cumulative burden"
      explanation; a persistently negative result would argue for genuine
      species-specific compensation and would strengthen the case for
      human-based models.
  evidence:
  - reference: PMID:12930822
    reference_title: "Parkin-deficient mice exhibit nigrostriatal deficits but not loss of dopaminergic neurons."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The number of dopaminergic neurons in the substantia nigra of parkin-/-
      mice, however, is normal up to the age of 24 months, in contrast to the
      substantial loss of nigral neurons characteristic of Parkinson's disease.
    explanation: >-
      The primary statement of the mismatch: the mouse knockout does not
      reproduce the defining human nigral degeneration even at 24 months.
  - reference: PMID:12930822
    reference_title: "Parkin-deficient mice exhibit nigrostriatal deficits but not loss of dopaminergic neurons."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Together these findings provide the first evidence for a novel role of
      parkin in dopamine regulation and nigrostriatal function, and a
      non-essential role of parkin in the survival of nigral neurons in mice.
    explanation: >-
      Explicitly frames parkin as non-essential for nigral neuron survival in
      mice, in direct tension with the human neuropathology.
  - reference: PMID:14985362
    reference_title: "Mitochondrial dysfunction and oxidative damage in parkin-deficient mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      provide the first direct evidence of mitochondrial dysfunction and
      oxidative damage in the absence of nigral degeneration in a genetic mouse
      model of Parkinson's disease
    explanation: >-
      Confirms the dissociation: the upstream mitochondrial/oxidative phenotype
      is faithfully modelled while the downstream degeneration is not.
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neuronal counts in the substantia nigra pars compacta revealed that
      neuronal loss in the parkin cases was as severe as that seen in PD
    explanation: >-
      The human side of the mismatch: severe nigral loss is unambiguous in
      biallelic parkin patients.
- discussion_id: gap_prkn_nigral_selectivity
  prompt: >-
    What makes substantia nigra pars compacta dopaminergic neurons - and
    specifically the ventral tier - selectively vulnerable to loss of
    parkin-dependent mitophagy, when parkin is broadly expressed and the
    PINK1-parkin pathway operates in all cell types?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Impaired Mitophagy
  - pathophysiology#Selective Dopaminergic Neuron Loss in the Substantia Nigra Pars Compacta
  rationale: >-
    Parkin is expressed in many human tissues, yet biallelic loss produces a
    strikingly organ- and even sub-nucleus-restricted phenotype: severe ventral
    nigral loss with relative dorsal-tier preservation, mild locus coeruleus and
    dorsal vagal involvement, and sparing of the nucleus basalis of Meynert and
    raphe. No mechanism in this entry's pathograph explains that selectivity;
    the mitophagy defect as modelled is cell-type agnostic. Resolving this is
    the difference between a generic mitochondrial-quality-control story and an
    account that predicts which neurons die. Candidate but unresolved factors
    include the exceptionally large unmyelinated axonal arbor and consequent
    bioenergetic load of nigral dopaminergic neurons, autonomous pacemaking with
    sustained calcium influx, dopamine metabolism as an endogenous oxidant
    source, and regional differences in baseline mitophagic flux.
  evidence:
  - reference: PMID:9560156
    reference_title: "Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 4.5-kilobase transcript that is expressed in many human tissues but is
      abundant in the brain, including the substantia nigra
    explanation: >-
      Establishes that parkin expression is broad, so expression alone does not
      account for the restricted phenotype.
  - reference: PMID:23459986
    reference_title: "Parkin disease: a clinicopathologic entity?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mild neuronal loss was identified in the locus coeruleus and dorsal motor
      nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe
      nucleus, or other brain regions.
    explanation: >-
      Documents the fine-grained regional selectivity that requires explanation.
references:
- reference: PMID:20301651
  title: "PRKN-Related Early-Onset Parkinson Disease."
  tags:
  - GeneReviews

📚

References & Deep Research

References

1

PMID:20301651

PRKN-Related Early-Onset Parkinson Disease.

No top-level findings curated for this source.

Deep Research

1

Claude Code ▸

PRKN-Related Juvenile/Early-Onset Parkinson Disease — Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 42 citations 2026-07-31T16:51:50.724886

PRKN-Related Juvenile/Early-Onset Parkinson Disease — Comprehensive Research Report

1. Disease Information

Overview. PRKN-related Parkinson disease (historically "autosomal recessive juvenile parkinsonism," AR-JP, or PARK2) is a monogenic, autosomal recessive form of early-onset parkinsonism caused by biallelic loss-of-function variants in PRKN (formerly PARK2), which encodes the E3 ubiquitin ligase parkin. It is the most common known monogenic cause of early-onset Parkinson disease (EOPD) GeneReviews, NBK1478. The clinical designation has shifted from "juvenile parkinsonism" (onset <21 years) to the broader PARK-PRKN / PRKN-Type Early-Onset Parkinson Disease, since the true age range at onset is 1–84 years with a median of 31 years GeneReviews, NBK1478.

Key identifiers: - OMIM phenotype: #600116 — Parkinson Disease 2, Autosomal Recessive Juvenile; PARK2 OMIM #600116 - OMIM gene: 602544 — Parkin RBR E3 Ubiquitin Protein Ligase; PRKN OMIM *602544 - MONDO: MONDO:0010820 — autosomal recessive juvenile Parkinson disease 2 ClinGen curation - Gene symbol: PRKN (previously PARK2); located at chromosome 6q26, one of the largest human genes (~1.38 Mb) - ICD-11: 8A00.0 (Parkinson disease), with genetic-etiology extension coding; ICD-10: G20 - MeSH:* Parkinson Disease (D010300); Parkinsonian Disorders

Synonyms: Autosomal recessive juvenile parkinsonism (AR-JP); Parkinson disease 2; PARK2; Parkin-type early-onset Parkinson disease (PARK-PRKN, in the current Mendelian nomenclature used by GeneReviews/MDSGene).

Data provenance: Information is derived from aggregated disease-level resources (OMIM, GeneReviews, ClinGen, MDSGene, Orphanet-linked literature reviews and meta-analyses of published case series and cohort studies), not from a single-patient EHR source.

2. Etiology

Disease causal factor: PRKN-PD is caused exclusively by biallelic (homozygous or compound heterozygous) pathogenic variants in PRKN that abolish or severely reduce parkin E3 ubiquitin ligase activity. It is a purely genetic/mechanistic (loss-of-function) disease with no known infectious cause; environmental exposures are not established causal factors, though they are studied as modifiers in idiopathic PD generally.

Genetic risk factors: - Causal (biallelic) variants: Deletions/duplications of whole exons account for roughly half of pathogenic alleles; among 159 disease-causing genotypes reviewed, 45.3% were structural variants (large deletions/duplications/indels/rearrangements), 30.2% were loss-of-function SNVs, and 20.8% were missense variants Frontiers, Genetic Analysis of EOPD, Eastern China. In some series, copy-number variants account for up to 60% of PRKN-PD cases. - Founder effects: A common exon 2 duplication identified in European populations was absent from non-European populations in gnomAD structural-variant data, suggesting a founder effect Frontiers, Heterozygous PRKN Variants CHRIS Cohort. - Heterozygous carriage: Population carrier frequency of PRKN pathogenic variants is estimated between 0.17% and 3.7% depending on population and ascertainment method. A large case-control genetic study found heterozygous PRKN mutations are common in the population but do not confer significantly increased Parkinson disease risk on their own Brain, Heterozygous PRKN mutations; a modest susceptibility effect combined with additional genetic or environmental risk factors cannot be excluded GeneReviews, NBK1478. - Modifier genes: No robustly validated modifier loci for PRKN-PD severity/onset are established; genotype–phenotype correlation across the >200 reported PRKN pathogenic variants has not been firmly established, as symptoms vary substantially even among individuals with the same genotype Frontiers, Genotype-Phenotype Correlations Monogenic PD.

Environmental risk/protective factors: Not specifically established for PRKN-PD; the broader PD literature implicates pesticide exposure, rural living, and traumatic brain injury as risk factors and caffeine/smoking as inversely associated (epidemiologic, not causal-confirmed) — these associations have not been specifically tested in PRKN-genotyped cohorts and should not be assumed to transfer directly.

Gene–environment interactions: No PRKN-specific gene–environment interaction studies were identified in this search; mechanistically, since parkin loss impairs clearance of oxidatively damaged mitochondria, environmental oxidative/mitochondrial stressors (e.g., rotenone, MPTP-like toxins) are plausible severity modifiers based on cellular models, but this is inferential rather than directly demonstrated in PRKN-PD patients.

3. Phenotypes

Cardinal motor signs (symptoms/signs; HPO/OMIM/GeneReviews-sourced): bradykinesia, resting tremor, rigidity, and postural instability — the core parkinsonian tetrad OMIM Clinical Synopsis #600116.

Phenotype	Category	Frequency/notes	Suggested HPO term (verify via OAK before curation)
Bradykinesia	Motor sign	Cardinal feature	HP:0002067 Bradykinesia
Resting tremor	Motor sign	Cardinal, common presenting sign	HP:0002322 Resting tremor
Rigidity	Motor sign	Cardinal feature	HP:0002063 Rigidity
Postural instability	Motor sign	Cardinal, typically later stage	HP:0002172 Postural instability
Lower-limb dystonia	Motor sign	Presenting sign in ~66% of individuals; may be isolated for years before parkinsonism	HP:0001332 Dystonia
Hyperreflexia	Motor sign	Present in ~50% of affected individuals; distinguishes from idiopathic PD	HP:0001347 Hyperreflexia
Levodopa-induced dyskinesia	Treatment-related sign	Higher likelihood than in non-genetic parkinsonism; early and sustained	HP:0002346 (Dyskinesia — verify)
Diurnal fluctuation / sleep benefit	Motor sign	Symptoms improve after sleep, worsen through the day — a distinguishing clinical clue	(no precise HPO; describe in notes)
Autonomic dysfunction (constipation, urinary frequency, sexual dysfunction, orthostatic hypotension)	Autonomic/laboratory-adjacent sign	~53% of individuals	HP:0002019 Constipation; HP:0000020 Urinary incontinence; HP:0001278 Orthostatic hypotension
Depression / anxiety	Behavioral	Frequent	HP:0000716 Depression; HP:0000739 Anxiety
Cognitive impairment / dementia	Behavioral/cognitive	Uncommon; dementia in <3%, no more frequent than general population	HP:0000726 (Dementia — rare in this disease)
Preserved olfaction	Sign (distinguishing, absence of typical feature)	"Well-preserved sense of smell" — contrasts with idiopathic PD hyposmia	HP:0004408 (Olfactory dysfunction — typically ABSENT here)

Source for the frequency and clinical-distinguishing data: GeneReviews, NBK1478; MalaCards.

Onset: Median 31 years, range 1–84 years; onset is usually before age 40; juvenile onset (<20 years) is comparatively rare but gives the disease its historical name.

Severity/progression: Slowly progressive — disease duration >60 years has been reported, substantially slower progression than idiopathic PD. Freezing of gait, postural deformities, and motor fluctuations may emerge in later stages, but dementia typically does not develop.

Quality of life impact: Levodopa-induced dyskinesia and early motor fluctuations are the dominant drivers of disability given the very long disease duration; autonomic symptoms (constipation, urinary, orthostatic) and mood symptoms (depression/anxiety) contribute meaningfully to quality of life over decades of disease, though formal EQ-5D/SF-36 PRKN-specific QoL studies were not identified in this search.

4. Genetic/Molecular Information

Causal gene: PRKN (HGNC symbol PRKN, previously PARK2), OMIM *602544, chromosome 6q26. PRKN spans ~1.38 Mb of genomic DNA with 12 exons, making it one of the largest genes in the human genome and overlapping the common fragile site FRA6E — a feature thought to predispose to the high rate of exonic structural rearrangements GeneReviews, NBK1478.

Pathogenic variant spectrum: - Pathogenic variants have been described across all 12 exons. - Structural/copy-number variants (exon deletions/duplications) are the single largest class (~45–60% depending on cohort) Frontiers EOPD China; complex structural variants including exon inversions can be invisible to standard exome sequencing and require targeted deletion/duplication or long-read sequencing methods to detect Brain Communications, Levodopa-responsive dystonia from PRKN exon inversion. - Loss-of-function SNVs (nonsense, frameshift, canonical splice-site): ~30%. - Missense variants: ~21%, often clustering in the RING/IBR zinc-binding domains where they destabilize protein folding. - Detection: sequence analysis alone detects ~39% of pathogenic alleles; gene-targeted deletion/duplication testing (MLPA, quantitative PCR, long-range PCR, targeted microarray, or long-read sequencing for complex rearrangements) is required to detect the remaining ~61% — single-gene sequencing-only testing is explicitly not recommended as a standalone approach GeneReviews, NBK1478; medRxiv, long-read sequencing PRKN structural variants.

Frequency in PD cohorts: PRKN biallelic pathogenic variants are found in 6–12% of PD with onset <50 years, 30% of onset <30 years, and up to 42.2% of onset ≤20 years GeneReviews, NBK1478; Central European EOPD cohorts show 2.6–9.3% prevalence of biallelic PRKN variants GeneReviews, NBK1478.

Functional consequence: The great majority of PRKN pathogenic variants act through loss of function of the E3 ubiquitin ligase — either by truncation/instability (nonsense, frameshift, most structural variants) or catalytic/structural inactivation (missense variants, especially in zinc-coordinating RING/IBR residues) GeneReviews, NBK1478.

Protein domain architecture: Parkin has an N-terminal ubiquitin-like (Ubl) domain followed by four zinc-coordinating domains: RING0 (also called the Unique Parkin Domain, UPD — interacts with PINK1), RING1 (E2-binding), IBR (in-between-RING, two zinc-binding sites required for correct folding), and RING2 (contains the catalytic cysteine, Cys431, required for E2-mediated ubiquitin transfer) GeneCards PRKN; PMC3730226, Structure of human Parkin ligase domain.

Modifier genes: None robustly established specific to PRKN-PD.

Somatic vs. germline: Exclusively germline in PRKN-PD (biallelic constitutional variants); no somatic mosaicism mechanism described for this disease.

Epigenetics / chromosomal abnormalities: No disease-defining epigenetic mechanism or large chromosomal aneuploidy is implicated; the relevant "structural variation" here is at the level of intragenic exon-level deletions/duplications/inversions rather than whole-chromosome abnormalities.

5. Environmental Information

No PRKN-PD-specific environmental, lifestyle, or infectious causal factors were identified in the literature searched. As a monogenic, fully penetrant-in-biallelic-carriers disease (see Section 9 for nuance on penetrance), environmental factors are not considered primary drivers, though — as in idiopathic PD — mitochondrial/oxidative toxicant exposure is mechanistically plausible as a severity modifier given the pathway involved (see Section 6).

6. Mechanism / Pathophysiology

Molecular function of parkin: Parkin is a cytosolic RBR (RING-Between-RING) E3 ubiquitin ligase central to mitochondrial quality control (mitophagy) and general proteasome-dependent protein degradation GeneCards PRKN.

Causal chain (PINK1–Parkin mitophagy pathway): 1. Trigger: Mitochondrial damage causes loss of inner-membrane potential, preventing the normal proteolytic removal of PINK1, which then accumulates and stabilizes on the outer mitochondrial membrane (OMM). 2. Activation: PINK1 phosphorylates pre-existing ubiquitin on OMM proteins at Ser65 and recruits/phosphorylates parkin's Ubl domain, releasing autoinhibition and activating parkin's E3 ligase activity J Cell Biol, PINK1 phosphorylates ubiquitin to activate Parkin. 3. Amplification: Activated parkin ubiquitinates additional OMM proteins (e.g., VDAC1, MFN1/2, MIRO1) via Lys-63-linked polyubiquitin chains, which PINK1 can again phosphorylate — a feedforward amplification loop that rapidly decorates damaged mitochondria with ubiquitin PMC9851250, Feedforward activation of PRKN/parkin. 4. Downstream execution: Ubiquitinated OMM proteins recruit autophagy receptors and the LC3/autophagosome machinery, marking damaged mitochondria for selective autophagic clearance (mitophagy) PMC9763867, Parkin-PHB2 interaction links inner membrane ubiquitination to mitophagy. 5. Disease consequence: Loss-of-function PRKN variants abolish or impair this quality-control step. Parkin-deficient cells cannot efficiently clear depolarized/damaged mitochondria; the accumulating burden of dysfunctional mitochondria drives chronic oxidative stress, decreased proteasome-mediated mitochondrial protein turnover, and ultimately apoptotic loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) — the anatomic hallmark shared with idiopathic PD Cyagen, PRKN Gene Function.

Cellular processes: mitophagy (GO:0000422), autophagy (GO:0006914), protein polyubiquitination (GO:0000209), ubiquitin-protein transferase/E3 ligase activity (GO:0061630 or GO:0004842), mitochondrion organization (GO:0007005), apoptotic cell death of vulnerable neurons/muscle (in model systems).

Metabolic context — differentiation-state dependence: A key mechanistic nuance from iPSC-neuron studies: when neuronal precursors are still glycolytic early in differentiation, mitophagy is unimpaired by PRKN deficiency; but as neurons mature and become dependent on oxidative phosphorylation, mitophagy becomes severely impaired in PRKN-mutant neurons PMC7511396, Oxidative switch drives mitophagy defects in parkin mutant patient neurons. This helps explain selective vulnerability of long-lived, highly oxidative dopaminergic neurons.

Oxidative stress: iPSC-derived PARK2 (PRKN) neurons and postmortem brain tissue show mitochondrial dysfunction, increased oxidative stress, and α-synuclein accumulation despite the characteristic absence of classical Lewy body pathology at autopsy in most PRKN-PD cases PMC3546866, Mitochondrial dysfunction with oxidative stress and α-synuclein accumulation in PARK2 iPSC neurons. Model-organism work (Drosophila) shows that antioxidant overexpression (glutathione S-transferase) rescues dopaminergic neurodegeneration in parkin mutants, supporting oxidative stress as a major downstream driver [PMC5818410].

Pathology (human): Loss of dopaminergic neurons in the substantia nigra similar to idiopathic PD, but classically without Lewy bodies — a key neuropathological distinction, although this is not absolute across all reported cases MalaCards; OMIM #600116.

Suggested ontology terms: GO:0000422 (mitophagy), GO:0006914 (autophagy), GO:0016567 (protein ubiquitination), GO:0004842/GO:0061630 (ubiquitin-protein ligase activity), GO:0007005 (mitochondrion organization); CL:0000700 (dopaminergic neuron); all should be verified against current OBO labels before curation (per dismech OAK-verification convention).

7. Anatomical Structures Affected

Organ/system level: Primary — central nervous system, specifically the basal ganglia dopaminergic circuit. Substantia nigra pars compacta (SNpc) dopaminergic neurons are the principal site of degeneration; the nigrostriatal projection to the striatum (caudate + putamen) is functionally denervated, producing the parkinsonian motor syndrome. Secondary/complication-level involvement includes the autonomic nervous system (gut, bladder, cardiovascular reflexes) accounting for the autonomic phenotype cluster.

Tissue/cell level: Dopaminergic neurons (CL:0000700) of the SNpc are the principal vulnerable population. Note that unlike idiopathic PD, locus coeruleus noradrenergic neurons and olfactory pathways are comparatively spared (consistent with preserved olfaction being a clinical distinguishing feature).

Subcellular level: Mitochondria (outer mitochondrial membrane specifically) are the central subcellular compartment implicated, via the PINK1-parkin mitophagy pathway; also the ubiquitin-proteasome system machinery broadly. Suggested GO Cellular Component terms: mitochondrial outer membrane (GO:0005741), mitochondrion (GO:0005739).

Localization (UBERON): substantia nigra (UBERON:0002038), basal ganglion (UBERON:0002420), brain (UBERON:0000955), striatum (UBERON:0002435) — terms should be verified via OAK/UBERON before use.

Lateralization: Typically bilateral, though — as in idiopathic PD — asymmetric onset (e.g., unilateral lower-limb dystonia or tremor) is common at presentation.

8. Temporal Development

Onset: Median age 31 years (range 1–84 years); onset is usually before age 40. Insidious/gradual onset is typical, consistent with a slowly evolving neurodegenerative process rather than acute or subacute presentation. Lower-limb dystonia may precede overt parkinsonism by years.

Progression: Slowly progressive over an unusually long disease course — disease duration exceeding 60 years has been documented, substantially longer than idiopathic PD GeneReviews, NBK1478. Motor progression rate is markedly slower than idiopathic PD. Later stages can include freezing of gait, postural deformities, and motor fluctuations, but — notably — dementia does not typically supervene even after decades, distinguishing the long-term course from idiopathic PD with dementia.

Course pattern: Progressive but with a characteristic diurnal fluctuation (symptoms worse later in the day) and sleep benefit (improvement after sleep) — a distinctive fluctuating component layered on the progressive baseline.

Treatment-response pattern: Marked, sustained levodopa responsiveness is a defining clinical feature, but with a higher-than-typical propensity for levodopa-induced dyskinesia, which becomes a dominant driver of later-stage disability/motor complications.

Critical periods: No formally defined developmental "critical window," but early recognition of the young-onset dystonia-parkinsonism phenotype is clinically important for genetic diagnosis and levodopa-dose optimization to minimize dyskinesia risk over a multi-decade disease course.

9. Inheritance and Population

Inheritance pattern: Autosomal recessive GeneReviews, NBK1478; heterozygotes (single pathogenic variant carriers) are not considered to have a strongly increased risk of disease on their own, though a modest susceptibility effect in combination with other genetic/environmental factors cannot be excluded Brain, Heterozygous PRKN mutations.

Recurrence risk: If both parents are confirmed heterozygous carriers, each sibling has at conception a 25% chance of being affected (biallelic), 50% chance of being an asymptomatic heterozygous carrier, and 25% chance of inheriting neither variant GeneReviews, NBK1478.

Penetrance: Notably incomplete even among biallelic carriers — in a population cohort, while biallelic PRKN carriers were more likely overall to carry a PD diagnosis, 91.7% of biallelic carriers identified through population screening were asymptomatic, reflecting substantial incomplete penetrance or an as-yet-unelapsed disease latency PMC8382284, Frequency of Heterozygous PRKN Variants and Penetrance, CHRIS Cohort.

Expressivity: Highly variable — no robust genotype-phenotype correlation has been established across the many different pathogenic PRKN alleles; clinical severity and symptom constellation vary substantially even for ostensibly similar genotypes Frontiers, Genotype-Phenotype Correlations Monogenic PD.

Genetic anticipation / germline mosaicism: Not a described feature of PRKN-PD (unlike repeat-expansion disorders).

Founder effects: The European exon 2 duplication is a well-documented founder allele, absent in non-European gnomAD structural-variant data Frontiers, CHRIS Cohort.

Carrier frequency / population prevalence: Heterozygous PRKN pathogenic variant carrier frequency is estimated at 0.17%–3.7% depending on population and methodology. A modeling study estimated genetic prevalence of PRKN-PD itself (biallelic) at approximately 24 per 100,000 in non-Japanese East Asians and 22 per 100,000 in Non-Finnish Europeans, the two highest-prevalence groups modeled (this is a preprint/medRxiv estimate and should be treated as provisional pending peer review) medRxiv, Estimated genetic prevalence of EOPD from PRKN mutations.

Consanguinity: As an autosomal recessive disease, consanguineous unions increase the probability of homozygosity for a given PRKN variant in populations/families where consanguinity is common; this is standard AR genetics reasoning rather than a PRKN-specific finding in the sources reviewed.

Sex ratio / geographic distribution: No strong sex-ratio skew is reported for PRKN-PD specifically in the sources reviewed (distinct from idiopathic PD's modest male excess). Geographic/ethnic variation in variant spectrum is well documented (e.g., European exon 2 duplication founder effect; differing structural-variant vs. point-mutation ratios reported in East Asian vs. European cohorts).

10. Diagnostics

Clinical suspicion criteria (no formal consensus criteria exist, but diagnosis should be suspected when): - Parkinsonism onset before ~age 40 (especially <20–30) - Prominent lower-limb dystonia, sometimes isolated for years - Hyperreflexia - Slow disease progression - Preserved olfaction (unusual for parkinsonism generally) - Marked, sustained levodopa response, but with early/prominent dyskinesia - Absence of dementia even after long disease duration GeneReviews, NBK1478

Genetic testing (definitive diagnosis): - Diagnosis requires demonstration of biallelic pathogenic PRKN variants. - Sequence analysis alone detects ~39% of pathogenic alleles; gene-targeted deletion/duplication analysis is essential (detects the remaining ~61%, given the high rate of exonic structural rearrangements) — techniques include quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and gene-targeted microarray GeneReviews, NBK1478. - Complex structural variants such as exon inversions can be invisible to standard exome sequencing and require MLPA or long-read sequencing for detection Brain Communications, PRKN exon inversion; medRxiv, long-read sequencing of PRKN structural variants. - Recommended testing strategy: multigene panel covering PRKN plus other EOPD genes (PINK1, PARK7/DJ-1, ATP13A2, DNAJC6, FBXO7, PLA2G6, SYNJ1, VPS13C), OR comprehensive genomic testing (exome/genome sequencing) combined with dedicated CNV analysis; single-gene sequencing-only testing is explicitly discouraged as insufficient.

Imaging: DAT-SPECT (¹²³I-ioflupane) demonstrates the expected nigrostriatal dopaminergic deficit consistent with any dopamine-deficient parkinsonism, confirming a neurodegenerative parkinsonism versus non-degenerative mimics, but does not distinguish PRKN-PD from idiopathic PD or other genetic forms AJNR, Role of DAT-SPECT in Parkinsonian Syndromes.

Emerging biomarkers: α-synuclein seed amplification assay (SAA) in CSF is a sensitive/specific marker for Lewy body disease; because PRKN-PD classically lacks Lewy body pathology, SAA status may theoretically differ from idiopathic PD, though PRKN-specific SAA data were not identified in this search and this should be treated as a hypothesis rather than an established diagnostic fact.

Differential diagnosis: - PARK-PINK1 (PINK1-related EOPD) — the second most common monogenic EOPD cause; clinically indistinguishable from PARK-PRKN, differentiated only by molecular testing GeneReviews, NBK1478 - PARK7 (DJ-1)-related parkinsonism - Other recessive EOPD/parkinsonism-plus genes: ATP13A2 (Kufor-Rakeb syndrome), DNAJC6, FBXO7, PLA2G6, SYNJ1, VPS13C - Dopa-responsive dystonia (GCH1, TH, SPR mutations) — important because of phenotypic overlap with the dystonia-predominant PRKN-PD presentation

Screening: No population-based newborn or general screening program exists for PRKN-PD given its adult/young-adult typical onset; targeted cascade testing of at-risk relatives (once a family's causal variants are known) and reproductive-partner carrier testing (particularly with known consanguinity) are the recommended screening applications. Prenatal diagnosis and preimplantation genetic testing are available once familial variants are identified GeneReviews, NBK1478.

11. Outcome/Prognosis

Survival/mortality: PRKN-PD is not directly life-shortening in the way many pediatric-onset genetic diseases are; disease duration exceeding 60 years has been documented, indicating survival compatible with a normal or near-normal lifespan, with morbidity driven by progressive motor disability rather than early mortality.

Morbidity/function: Long-term disability accrues from: (1) progressive core parkinsonian motor impairment (bradykinesia, rigidity, gait freezing, postural instability in later stages), and (2) treatment-related motor complications, especially levodopa-induced dyskinesia, which tends to appear earlier and more prominently than in idiopathic PD and becomes a major determinant of quality of life over a multi-decade disease course.

Preserved domains: Cognitive function is relatively preserved — dementia is rare (<3%) and, per available data, roughly comparable to general-population rates, a strikingly different long-term trajectory than idiopathic PD, where PD-associated dementia is common in advanced disease.

Complications: Autonomic complications (constipation, urinary dysfunction, orthostatic hypotension) and psychiatric symptoms (depression, anxiety) are frequent contributors to morbidity; falls/postural instability become relevant in advanced stages.

Prognostic factors: No robust genotype-specific prognostic biomarkers have been established (see Section 9, expressivity); disease duration and the emergence of dyskinesia/motor fluctuations are the dominant clinically tracked prognostic markers, managed proactively by minimizing levodopa dose above the minimum effective threshold.

12. Treatment

Pharmacotherapy (first-line and adjunctive): - Levodopa (with peripheral decarboxylase inhibitor) — first-line; produces a "marked and sustained response," the most distinctive treatment feature of this disease GeneReviews, NBK1478. Suggested NCIT term: NCIT:C15986 (Pharmacotherapy) as treatment_term with therapeutic_agent bound to levodopa (verify CHEBI/NCIT ID via OAK). - Dopamine receptor agonists - Monoamine oxidase type B (MAO-B) inhibitors - Catechol-O-methyltransferase (COMT) inhibitors - Amantadine - Adenosine A2A receptor antagonists - Anticholinergics (useful especially for dystonia-predominant presentations) GeneReviews, NBK1478

Critical dosing caution: Because of the elevated risk of levodopa-induced dyskinesia in this population, clinicians are specifically advised to avoid levodopa doses that exceed what is needed for satisfactory clinical response GeneReviews, NBK1478.

Agents to avoid: Dopamine-blocking drugs — both typical/atypical antipsychotics and dopamine-blocking antiemetics/GI agents — can exacerbate parkinsonism and should be avoided when possible GeneReviews, NBK1478.

Surgical/device therapy: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or globus pallidus internus (GPi) is appropriate for individuals with disabling motor fluctuations/dyskinesia refractory to medical optimization. STN DBS's antidyskinetic effect is largely mediated through allowing reduction of dopaminergic medication dose, whereas GPi stimulation has more direct antidyskinetic effects PMC4010755, Surgical Treatment of Dyskinesia in PD. Modern DBS series report ≥50% symptom reduction and roughly 4 additional hours of "ON" time daily in PD generally (not PRKN-specific figures).

Supportive/rehabilitative care: Physical therapy, occupational therapy, speech/voice therapy (e.g., Lee Silverman Voice Treatment), and structured exercise (aerobic, strength training, Tai Chi) are recommended; management of constipation, sleep disturbance, and orthostatic hypotension is part of routine longitudinal care.

Experimental/advanced therapeutics: - AAV9-PRKN gene replacement therapy — preclinical: AAV9 vectors (e.g., AAV9-PK041, developed at Takeda) restore parkin expression in dopaminergic neurons and protect nigral dopaminergic neurons in 6-OHDA-lesion and α-synuclein preformed-fibril mouse models of PD Gene Therapy (Nature), In vitro/vivo rescue of dopaminergic neurons after Parkin gene therapy; PMC12263715, Investigational Gene Therapies for PD. No completed human clinical trial specific to PRKN-PD gene replacement was identified in this search (as of this report). - Splice-intervention (antisense oligonucleotide) therapy targeting specific PRKN exon-deletion genotypes has been described preclinically as a strategy to restore an in-frame, functional transcript for particular structural variants PMC7582384, Splice Intervention Therapy for AR Juvenile PD from Parkin mutations. Suggested therapeutic_modality: ANTISENSE_OLIGONUCLEOTIDE with aso_mechanism SPLICE_MODULATION_EXON_SKIPPING/INCLUSION depending on the specific variant targeted, once a specific clinical-stage candidate and molecular target (exon number) are identified from primary literature.

Treatment outcomes: Response rates to levodopa in PRKN-PD are characteristically excellent and durable relative to idiopathic PD; the principal adverse "cost" is the elevated rate of levodopa-induced dyskinesia (general PD literature: ~40% of patients affected by 4 years of levodopa use, 50–80% by 5–10 years) PMC12583070, Levodopa-induced dyskinesia review; PRKN-PD patients are considered to have proportionally higher dyskinesia liability than average.

Treatment strategy: No PRKN-specific formal treatment algorithm/guideline distinct from general early-onset PD management was identified; the core personalized-medicine principle specific to this disease is genetic confirmation to (a) counsel patients on the expected long, dyskinesia-prone but cognitively spared disease course, (b) guide conservative levodopa titration, and (c) inform family genetic counseling.

13. Prevention

Primary prevention: Not applicable in the traditional sense (no modifiable environmental cause established); the relevant "primary prevention" lever is reproductive/genetic — carrier screening and reproductive counseling in families with a known proband, and prenatal/preimplantation genetic testing once familial PRKN variants are identified GeneReviews, NBK1478.

Secondary prevention: Early genetic diagnosis in individuals presenting with young-onset dystonia-parkinsonism allows earlier, dose-conservative levodopa initiation aimed at minimizing later dyskinesia burden — the closest analog to "early detection and treatment" for this disease.

Genetic counseling: Central to family management — explaining the 25% recurrence risk for future siblings when both parents are confirmed carriers, offering heterozygote (carrier) testing to at-risk relatives once the familial variants are known, and discussing incomplete penetrance (most biallelic carriers identified outside a clinical ascertainment context are asymptomatic) so that genetic results are interpreted with appropriate caution GeneReviews, NBK1478; PMC8382284, CHRIS Cohort penetrance data.

Screening: No population-based newborn or adult screening program exists; targeted family (cascade) screening is the applicable model.

Public health/immunization/behavioral prevention: Not applicable — no infectious, vaccine-preventable, or established behavioral-risk component to this monogenic disease.

14. Other Species / Natural Disease

No naturally occurring PRKN-orthologous parkinsonism has been documented in companion animals or wildlife in the sources reviewed (this is a human genetic disease without a recognized veterinary natural-disease counterpart, unlike, e.g., some lysosomal storage disorders with dog/cat models). The disease-relevant biology is instead studied through engineered model organisms (Section 15). Human PRKN taxon: NCBITaxon:9606 (Homo sapiens).

15. Model Organisms

Drosophila melanogaster (parkin null mutants): The most phenotypically robust invertebrate model. Parkin-null flies show reduced lifespan, locomotor defects, male sterility, and dramatic mitochondrial pathology — swollen mitochondria with severely fragmented cristae — concentrated in energy-intensive tissues, especially adult flight muscle, which ultimately undergoes apoptotic degeneration; modest dopaminergic neurodegeneration is also observed PNAS, Mitochondrial pathology and apoptotic muscle degeneration in Drosophila parkin mutants; [ScienceDirect, Parkin Mutant Drosophila overview]. This model strongly supports the mitochondrial-quality-control mechanism and is widely used for genetic modifier screens (e.g., rescue by antioxidant gene overexpression) PMC5818410; PMC9598960, Folic acid rescue of Parkin-null Drosophila phenotypes.

Mouse (Mus musculus): - Constitutive Prkn knockout mice largely fail to recapitulate the dopaminergic neuronal loss and motor impairment seen in human PRKN-PD, despite showing mitochondrial dysfunction and broad proteomic changes — a long-standing puzzle in the field Nature npj Parkinson's Disease, PARKIN is not required to sustain OXPHOS function in adult mammalian tissues. One proposed explanation: germline (from-birth) Prkn deletion triggers developmental genetic compensation, whereas adult-onset Prkn deletion via lentiviral delivery does produce progressive dopamine neuron loss — implicating a compensation mechanism specific to constitutive knockouts [search synthesis, multiple sources]. - Prkn R275W knock-in mice (a disease-relevant missense allele rather than a null) represent a more accurate model, showing early dopamine neuron dysfunction, age-dependent substantia nigra dopamine neuron loss, and progressive motor impairment — considered a superior model of human juvenile parkinsonism relative to constitutive knockouts PMID:39350737 / Brain 2024, Dopamine neuron dysfunction and loss in the Prkn R275W mouse model of Juvenile Parkinsonism. - Prkn-knockout mice additionally show autistic-like behaviors and aberrant synapse formation, suggesting broader circuit-level roles for parkin beyond dopaminergic neurodegeneration PMC9249611, Prkn knockout mice autistic-like behaviors. - A combined parkin-Pacrg knockout line and an isolated Pacrg knockout line have also been generated and characterized, given the overlapping genomic locus of PRKN and PACRG Scientific Reports, parkin-Pacrg knockout mouse.

Zebrafish (Danio rerio): Transient antisense (morpholino) knockdown of parkin does not produce morphological or behavioral abnormalities, and no dopaminergic neuron loss is observed — a negative/limited model. Conversely, transgenic zebrafish overexpressing parkin are protected from proteotoxic-stress-induced cell death, supporting a protective/quality-control role for parkin even though loss-of-function knockdown alone is insufficient to produce an overt phenotype in this system PLOS ONE, Parkin Is Protective against Proteotoxic Stress in a Transgenic Zebrafish Model.

Human iPSC-derived neuronal models: PARK2 (PRKN) patient-derived iPSC neurons and postmortem brain tissue show mitochondrial dysfunction, increased oxidative stress, and α-synuclein accumulation, providing a human cellular correlate of the pathway PMC3546866. Mitophagy defects in these neurons are unmasked specifically as cells transition to oxidative-phosphorylation dependence during differentiation, offering a plausible explanation for selective adult-onset dopaminergic vulnerability despite germline gene loss from conception PMC7511396. Skin fibroblasts from PRKN-PD patients also show mitochondrial and autophagic alterations, useful as an accessible non-neuronal patient cell model PMC6594812, Mitochondrial and autophagic alterations in PD patient fibroblasts with Parkin mutations.

Human-model translational gap (flag for curation as a HUMAN_MODEL_MISMATCH candidate): The striking discrepancy between constitutive Prkn-knockout mice (minimal phenotype) and the clear human disease phenotype is a well-recognized, unresolved translational-fidelity gap in the field — the R275W knock-in and adult-conditional-deletion models represent partial resolutions but the mechanistic basis of developmental compensation remains "unknown" per the primary sources Nature npj Parkinson's Disease 2024.

Summary of Key Ontology Term Candidates (verify all via OAK before curation)

Domain	Suggested term	ID (verify)
Disease	autosomal recessive juvenile Parkinson disease 2	MONDO:0010820
Gene	PRKN	hgnc:8607 (verify)
Phenotype	Bradykinesia	HP:0002067
Phenotype	Resting tremor	HP:0002322
Phenotype	Rigidity	HP:0002063
Phenotype	Dystonia	HP:0001332
Phenotype	Hyperreflexia	HP:0001347
Phenotype	Orthostatic hypotension	HP:0001278
Phenotype	Constipation	HP:0002019
Phenotype	Depression	HP:0000716
GO Biological Process	mitophagy	GO:0000422
GO Biological Process	protein polyubiquitination	GO:0000209
GO Molecular Function	ubiquitin-protein transferase activity	GO:0004842
Cell type	dopaminergic neuron	CL:0000700
Anatomy	substantia nigra	UBERON:0002038
Anatomy	basal ganglion	UBERON:0002420
Chemical	levodopa	CHEBI:6437
Chemical	dopamine	CHEBI:18243
Treatment	Pharmacotherapy	NCIT:C15986
Treatment	Gene Therapy	NCIT:C15238
Treatment	Deep Brain Stimulation (Device)	verify NCIT term

Sources

Caveat on citation format: The above are review/database/aggregator citations rather than exact primary-literature PMIDs for every claim; for dismech KB curation, each specific evidence: block should be traced back to its primary PubMed-indexed source (e.g., the original GeneReviews-cited studies, the specific cohort papers underlying the 6–12%/30%/42.2% frequency figures, and the primary Drosophila/mouse/zebrafish papers) and verified per the dismech reference-validation SOP (just fetch-reference PMID:XXXX + just validate-references) before being committed as PMID-anchored snippets.

PRKN-Related Juvenile Parkinson Disease

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PRKN-Related Juvenile/Early-Onset Parkinson Disease — Comprehensive Research Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

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

Summary of Key Ontology Term Candidates (verify all via OAK before curation)

Sources