Amyotrophic Lateral Sclerosis

Complex MONDO:0004976 Pathograph 21 Show in embeddings browser Motor Neuron Disease Neurodegenerative Disease

Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a progressive neurodegenerative disorder characterized by the selective death of upper and lower motor neurons in the brain, brainstem, and spinal cord. This leads to progressive muscle weakness, atrophy, spasticity, and ultimately respiratory failure. ALS typically presents in adulthood with a median survival of 3-5 years from symptom onset. Approximately 5-10% of cases are familial, with the remainder being sporadic. A hallmark feature is TDP-43 proteinopathy, present in approximately 97% of cases.

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Classifications

Harrison's Chapter

Mechanistic Nosology

◆

Subtypes

Familial ALS

Hereditary form of ALS accounting for 5-10% of cases, with mutations in genes such as SOD1, C9orf72, TARDBP, and FUS.

Sporadic ALS

Non-hereditary form of ALS accounting for 90-95% of cases with unclear etiology.

Bulbar-onset ALS

ALS beginning with speech and swallowing difficulties due to bulbar motor neuron involvement.

Limb-onset ALS

ALS beginning with limb weakness, the most common presentation.

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Mechanistic Hypotheses

Canonical Motor Neuron Proteostatic Failure Model

canonical_motor_neuron_proteostatic_failure_model CANONICAL

Evidence balance 1 support 1 partial

Progressive upper and lower motor neuron degeneration in ALS is the convergent endpoint of multiple genetic and sporadic insults that ultimately cause proteostatic failure. Key drivers include cytoplasmic mislocalization and aggregation of TDP-43 (in >97% of cases), C9orf72 hexanucleotide repeat expansion–derived dipeptide repeats and RNA foci, SOD1 misfolding, FUS/EWSR1 phase-separation defects, impaired autophagy, mitochondrial dysfunction, axonal transport failure, and neuroinflammation. Selective vulnerability of cortical layer-5 Betz cells and spinal alpha motor neurons leads to progressive muscle denervation, weakness, atrophy, and ultimately respiratory failure. Antisense-oligonucleotide therapy targeting SOD1 (tofersen) provides the strongest interventional validation of the SOD1 genetic-pathogenetic axis of this canonical multi-hit model; the C9orf72 ASO program (BIIB078) was discontinued after Phase 1 without clinical benefit, indicating that RNA-foci reduction alone is insufficient and DPR-mediated toxicity likely dominates the C9orf72 axis.

Retained as CANONICAL. The 2026 openscientist hypothesis-search report (kb/hypotheses/Amyotrophic_Lateral_Sclerosis/canonical_motor_neuron_proteostatic_failure_model) confirms convergent proteostatic failure as the unifying ALS mechanism: TDP-43 proteinopathy in ~97% of cases, SOD1 misfolding, C9orf72 RNA foci and DPRs, FUS phase-separation defects, impaired autophagy, mitochondrial dysfunction, axonal transport failure, and neuroinflammation all converge on motor-neuron degeneration. Tofersen (SOD1 ASO) approval provides the strongest causal validation of the genetic-pathogenetic axes. Three qualifications: (1) the C9orf72-ASO program (BIIB078; Phase 1 discontinued) showed insufficient clinical efficacy — RNA-foci reduction does not consistently translate to motor preservation, suggesting DPR-mediated toxicity may dominate; (2) the "proteostatic failure" framing remains a descriptive convergence rather than a single mechanistic primer — different genetic ALS subtypes follow different upstream paths; (3) sporadic ALS (~90%) requires environmental/epigenetic modifiers (BMAA, head trauma, aging) that the canonical model does not specify.

Deep research

OpenScientist citations 35 citations 2026-05-23T16:01:09.200504

Show evidence (2 references)

PMID:38891021 SUPPORT Human Clinical

"upper and lower motor neurons in the brain and spinal cord progressively degenerate"

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

PMID:39986312 PARTIAL Human Clinical

"Clinical trials using antisense oligonucleotides to target the GGGGCC repeat RNA have not been successful, potentially because they only target a single gain-of-function mechanism."

Lancet Neurology 2025 review confirms that C9orf72 ASO trials did not achieve clinical benefit, directly qualifying the canonical model's genetic-pathogenetic-axis interventional validation. The hexanucleotide repeat expansion drives a complex interplay of loss-of-function and gain-of-function pathology that single-target therapies do not address.

TDP-43 RNA Dysregulation and Motor-Neuron Selective Vulnerability Model

tdp43_rna_dysregulation_selective_vulnerability_model EMERGING

Evidence balance 4 support

This focused model treats ALS-associated TDP-43 pathology as a coupled nuclear loss-of-function and cytoplasmic gain-of-function process. Nuclear depletion of TDP-43 removes cryptic-exon repression and other RNA-processing controls in vulnerable motor neurons, producing mis-spliced or unstable transcripts such as STMN2 and UNC13A that impair axonal repair, synaptic function, and proteostasis. Cytoplasmic TDP-43 aggregation may amplify injury through stress-granule and proteostatic dysfunction and may contribute to propagation, but the unresolved causal step is which RNA target, aggregate species, or non-cell-autonomous signal converts TDP-43 dysfunction into selective motor-neuron death.

The 2026 OpenScientist hypothesis report (kb/hypotheses/Amyotrophic_Lateral_Sclerosis/tdp43_rna_dysregulation_selective_vulnerability_model) judged the TDP-43 loss-of-function/cryptic-exon arm to be the strongest, best-supported part of this hypothesis, while keeping the integrated model of RNA loss, cytoplasmic gain-of-function, selective vulnerability, and propagation as emerging because the rate-limiting RNA target, aggregate species, upstream trigger hierarchy, and spread mechanism remain unresolved. Additional report-suggested PMIDs were retained as curation leads and not added here without independent PubMed/cache verification.

Pathograph links

TDP-43 Proteinopathy -> TDP-43-Dependent Cryptic Exon Misprocessing DIRECT Nuclear depletion of TDP-43 removes repression of cryptic exons and cryptic splice-polyadenylation events in disease-relevant transcripts.

TDP-43-Dependent Cryptic Exon Misprocessing -> Axonal Transport Dysfunction INDIRECT KNOWN INTERMEDIATES STMN2 loss and related RNA misprocessing can impair axonal outgrowth, axon regeneration, and lysosome trafficking in human motor-neuron models. Intermediates: STMN2 depletion; impaired axonal regeneration; stathmin-2-dependent lysosome trafficking defects

TDP-43-Dependent Cryptic Exon Misprocessing -> Motor Neuron Degeneration INDIRECT KNOWN INTERMEDIATES Cryptic-exon misprocessing is modeled as an indirect, target-specific bridge from TDP-43 nuclear loss to motor-neuron degeneration through STMN2-dependent axonal repair defects, UNC13A-dependent synaptic defects, and other transcript-specific losses. Intermediates: STMN2 depletion and impaired axonal repair; UNC13A nonsense-mediated decay and synaptic dysfunction; unresolved additional TDP-43 RNA targets

Deep research

OpenScientist citations 37 citations 2026-06-03T09:22:30.171915

Show evidence (4 references)

PMID:32799899 SUPPORT Other

"Research has focused on the formation and consequences of cytosolic protein aggregates as drivers of ALS pathology through both gain- and loss-of-function mechanisms."

Review-level synthesis supports modeling TDP-43 pathology as both nuclear loss-of-function and cytoplasmic gain-of-function rather than as aggregation alone.

PMID:26250685 SUPPORT Human Clinical

"repression of cryptic exons was impaired in ALS-FTD cases, suggesting that this splicing defect could potentially underlie TDP-43 proteinopathy."

Human ALS-FTD tissue evidence links loss of TDP-43 cryptic-exon repression to TDP-43 proteinopathy.

PMID:30643292 SUPPORT In Vitro

"STMN2 loss upon reduced TDP-43 function was due to altered splicing, which is functionally important, as we show STMN2 is necessary for normal axonal outgrowth and regeneration."

Human motor-neuron experiments identify STMN2 mis-splicing and loss as a functional downstream RNA target that impairs axonal growth and repair.

+ 1 more reference

Discussions and Knowledge Gaps

Which TDP-43-dependent RNA-processing defect, cytoplasmic aggregate species, or non-cell-autonomous signal explains why upper and lower motor neurons are selectively vulnerable in ALS, and how does this mechanism relate to clinical propagation across neuroanatomical regions?

KNOWLEDGE GAP OPEN gap_als_tdp43_selective_vulnerability_and_spread

Attached to

mechanistic_hypothesis#tdp43_rna_dysregulation_selective_vulnerability_model pathophysiology#TDP-43 Proteinopathy pathophysiology#TDP-43-Dependent Cryptic Exon Misprocessing pathophysiology#Motor Neuron Degeneration

STMN2 and UNC13A make TDP-43 loss-of-function concrete at the RNA target level, but they do not yet explain why particular motor-neuron classes degenerate while other neurons or glia with TDP-43 pathology can be less affected. Separating nuclear RNA loss-of-function from cytoplasmic gain-of-function and spread-like propagation is required to decide whether therapies should prioritize restoring individual transcripts, correcting TDP-43 localization, clearing aggregate species, or targeting glial and circuit-level amplifiers.

Proposed experiments

Isogenic human motor-neuron TDP-43 target rescue and spatial validation panel

isogenic stem-cell perturbation and spatial transcriptomics experiment

exp_als_isogenic_motor_neuron_tdp43_target_rescue_panel

Compare isogenic human iPSC-derived upper- and lower-motor-neuron-like cultures with controlled nuclear TDP-43 depletion, TDP-43 cytoplasmic mislocalization, and patient-derived TDP-43 aggregate seeding. Rescue STMN2, UNC13A, and candidate transcript targets singly and in combination, then benchmark survival, axonal regeneration, synaptic function, lysosome trafficking, and spatial transcriptomic signatures against ALS postmortem motor cortex and spinal cord.

Decision criterion

A causal RNA-processing target should rescue motor-neuron survival or axonal/synaptic function in TDP-43-deficient cells and show spatially concordant misprocessing in vulnerable human ALS motor-neuron populations; failure of target rescue would shift priority toward aggregate-seeding, proteostatic, glial, or circuit-level propagation mechanisms.

Show evidence (2 references)

PMID:37999738 SUPPORT Other

"Despite extensive research, it remains unclear why some motor neurons are especially susceptible to the disease, while others are affected less or even spared."

Review explicitly frames motor-neuron selective vulnerability as an unresolved ALS mechanism.

PMID:32799899 SUPPORT Other

"Yet in ALS, motor neurons selectively degenerate suggesting that the presence of TDP-43 aggregates may not necessarily drive cell-death."

TDP-43 review highlights the unresolved gap between aggregate presence and selective motor-neuron death.

What upstream cellular event triggers preferential TDP-43 nuclear clearance and cytoplasmic mislocalization in motor neurons compared with other cell types that also express TDP-43?

KNOWLEDGE GAP OPEN gap_als_tdp43_mislocalization_upstream_trigger

Attached to

pathophysiology#TDP-43 Proteinopathy mechanistic_hypothesis#tdp43_rna_dysregulation_selective_vulnerability_model

TDP-43 is a ubiquitously expressed nuclear RNA-binding protein, yet in ALS it mislocalizes and aggregates preferentially in motor neurons. The NLS and NES sequences of TDP-43 are not motor-neuron specific, and cellular stressors such as oxidative stress, osmotic stress, or heat shock can induce phase-separated TDP-43 cytoplasmic structures in many cell types. What makes motor neurons uniquely susceptible to irreversible TDP-43 mislocalization — whether through long-axon-specific transport burdens, particular importin isoform expression, differential proteostatic capacity, or a specific upstream metabolic vulnerability — is not established. Identifying this upstream trigger is required to explain why ALS is a motor-neuron disease rather than a pan-neuronal or pan-cellular proteinopathy, and to determine the earliest actionable intervention point.

Show evidence (2 references)

PMID:32799899 SUPPORT Other

"The exact mechanisms mediating the formation of TDP-43 aggregates remain elusive."

Review acknowledges that the upstream trigger for TDP-43 aggregation and mislocalization is unresolved, supporting this as an open knowledge gap distinct from the downstream RNA-processing defects.

PMID:37999738 SUPPORT Other

"Despite extensive research, it remains unclear why some motor neurons are especially susceptible to the disease, while others are affected less or even spared."

Selective vulnerability review frames the motor-neuron-preferential degeneration as unresolved, implicating upstream cell-type-specific factors in TDP-43 mislocalization as a key open question.

Does phosphorylated TDP-43 pathology spread through the ALS motor system by prion-like protein seeding, by trans-synaptic or retrograde axonal signaling, or by secondary neuroinflammatory relay — and can these mechanisms be distinguished experimentally?

KNOWLEDGE GAP OPEN gap_als_ptdp43_propagation_mechanism

Attached to

pathophysiology#TDP-43 Proteinopathy pathophysiology#Motor Neuron Degeneration mechanistic_hypothesis#tdp43_rna_dysregulation_selective_vulnerability_model

Cross-sectional postmortem staging studies show that pTDP-43 pathology progresses through the ALS motor system in a stereotyped, anatomically sequential pattern analogous to Braak staging in Parkinson disease and Alzheimer disease, consistent with a propagating process. However, the cellular mechanism of spread is not established: whether pTDP-43 propagates by direct cell-to-cell protein seeding (prion-like templating), by trans-synaptic or retrograde axonal transport of a pathological signal, by secondary glial or neuroinflammatory relay, or by some combination of these mechanisms remains unresolved. Understanding the propagation mechanism has direct therapeutic implications — a seeding model prioritizes aggregate clearance or passive immunotherapy at early disease stages, while an inflammatory-relay model prioritizes anti-neuroinflammatory intervention at transitional anatomical boundaries.

Show evidence (2 references)

PMID:23686809 SUPPORT Human Clinical

"pTDP-43 pathology in ALS possibly disseminates in a sequential pattern that permits recognition of 4 neuropathological stages consistent with the hypothesis that pTDP-43 pathology is propagated along axonal pathways."

Postmortem staging data in 76 ALS cases support sequential anatomical spread of pTDP-43 pathology, motivating the mechanistic question of how this propagation is achieved without establishing the cellular mechanism.

PMID:23686809 PARTIAL Human Clinical

"Whereas the cell-to-cell transmission of pTDP-43 has not been demonstrated conclusively in vivo, a recently discovered C-terminal prion-like domain has been implicated in the aggregation of pTDP-43 in cultured cells."

In vitro prion-like domain evidence is consistent with protein seeding but does not establish in vivo cell-to-cell transmission, leaving the propagation mechanism open.

Does the lower-motor-neuron-only phenotype of equine motor neuron disease (EMND) preclude its use as a model for classic ALS, which requires both upper and lower motor neuron degeneration?

HUMAN MODEL MISMATCH OPEN mismatch_emnd_lmn_only_phenotype

Attached to

animal_model#Horse

Classic ALS is defined by combined upper motor neuron (UMN) and lower motor neuron (LMN) degeneration. Equine motor neuron disease (EMND) involves predominantly or exclusively lower motor neurons, with no established corticospinal tract involvement, making it a phenotypically closer analog to progressive muscular atrophy (LMN-only ALS variant) than to classic ALS. This reduces the direct translational value of EMND as an ALS model, though the shared oxidative stress mechanism and spinal motor neuron vulnerability retain biological relevance for the LMN degenerative arm of the disease.

Proposed experiments

Corticospinal tract histopathological survey in EMND horses

post-mortem neuropathological study

exp_emnd_umn_tract_assessment

Systematic immunohistochemical and histopathological assessment of corticospinal tracts and motor cortex in post-mortem EMND horses to determine whether subclinical UMN pathology is present but overlooked in existing case series, or is genuinely absent.

Decision criterion

Detection of UMN pathology would support EMND as a true ALS analog; confirmed absence would classify EMND as a selective LMN disease and redirect its value to studies of the ALS LMN degenerative arm only.

⚙

Pathophysiology

Motor Neuron Degeneration

Progressive death of upper motor neurons in the motor cortex and lower motor neurons in the brainstem and spinal cord leads to denervation of skeletal muscles. The loss of upper motor neurons causes spasticity and hyperreflexia, while lower motor neuron loss results in muscle weakness, atrophy, and fasciculations.

motor neuron CL:0000100

primary motor cortex UBERON:0001384

Show evidence (4 references)

ORPHA:803 SUPPORT

"A neurodegenerative disease characterized by progressive muscular paralysis reflecting degeneration of motor neurons in the primary motor cortex, corticospinal tracts, brainstem and spinal cord."

Orphanet definition confirms progressive motor neuron degeneration across cortex, brainstem, and spinal cord.

PMID:38521060 SUPPORT Human Clinical

"we identify known and previously unidentified vulnerable populations in cortical layer 5 and show that ALS- and FTLD-implicated motor and spindle neurons possess a virtually indistinguishable molecular identity."

Single-cell atlas of human ALS motor cortex identifies vulnerable neuronal populations in cortical layer 5 (including ALS-implicated motor/spindle neurons), supporting selective cortical motor-neuron vulnerability.

PMID:38891021 SUPPORT

"upper and lower motor neurons in the brain and spinal cord progressively degenerate during the course of the disease, leading to the loss of the voluntary movement of the arms and legs."

Review summarizes canonical ALS pathology of progressive upper and lower motor neuron degeneration causing loss of voluntary movement.

+ 1 more reference

Nuclear Pore Complex Dysfunction

Selective loss of nuclear pore complex (NPC) components, particularly the scaffold proteins NUP107 and NUP93 and FG-repeat-containing components, is a consistent feature across ALS postmortem spinal cord, SOD1^G93A and TDP-43 mutant mouse models, and human cell systems. CRISPR-mediated NUP107 depletion is sufficient to trigger cytoplasmic TDP-43 mislocalization, increased TDP-43 phosphorylation, and autophagy dysfunction, placing NPC dysfunction upstream of TDP-43 proteinopathy in the canonical proteostatic failure cascade. Oxidative stress exacerbates NPC subunit mislocalization, creating a redox-sensitive vulnerability that amplifies the downstream TDP-43 aggregation phenotype.

motor neuron CL:0000100

NUP50 hgnc:8065 GLE1 hgnc:4315

nucleocytoplasmic transport GO:0006913 ↓ DECREASED

Downstream

TDP-43 Proteinopathy NPC scaffold loss permits cytoplasmic TDP-43 mislocalization, hyperphosphorylation, and autophagy dysfunction.

Show evidence (3 references)

PMID:40819564 SUPPORT In Vitro

"CRISPR-mediated depletion of NUP107 in human cells triggers hallmark features of ALS pathology, including cytoplasmic TDP-43 mislocalization, increased phosphorylation, and autophagy dysfunction."

Direct CRISPR perturbation demonstrating that NPC dysfunction is sufficient to reproduce hallmark ALS molecular pathology, including TDP-43 cytoplasmic mislocalization, phosphorylation, and autophagy disruption. Establishes NPC dysfunction as an upstream driver of the canonical TDP-43 proteinopathy axis.

PMID:40819564 SUPPORT Human Clinical

"selective loss of NPC components, particularly the scaffold proteins NUP107 and NUP93, and FG-repeat-containing components-is a consistent finding across ALS postmortem spinal cord"

Postmortem human ALS spinal cord shows selective NPC scaffold loss, confirming NPC dysfunction in human disease.

PMID:40819564 SUPPORT Model Organism

"selective loss of NPC components, particularly the scaffold proteins NUP107 and NUP93, and FG-repeat-containing components-is a consistent finding across ALS postmortem spinal cord, SOD1^G93A and TDP-43 mutant mouse models, and human cell systems"

Convergent NPC dysfunction in SOD1^G93A and TDP-43 mutant mouse models confirms this finding is not a model-system artifact and supports cross-species generalizability of the mechanism.

TDP-43 Proteinopathy

Cytoplasmic aggregation of TDP-43 (TAR DNA-binding protein 43) is found in approximately 97% of ALS cases, with notable exceptions such as SOD1- and FUS-associated ALS. TDP-43 normally functions as a predominantly nuclear RNA-binding protein. In ALS it becomes depleted from the nucleus and accumulates in cytoplasmic phosphorylated, ubiquitinated inclusions, creating a coupled loss-of-nuclear-function and cytoplasmic gain-of-function state. The nuclear loss arm impairs RNA processing and cryptic-exon repression, while cytoplasmic aggregation may block normal cellular processes, disturb proteostasis, and participate in spread-like propagation.

TDP-43 RNA Dysregulation and Motor-Neuron Selective Vulnerability Model

TARDBP hgnc:11571

RNA processing GO:0006396 ⚠ ABNORMAL RNA splicing GO:0000375 ⚠ ABNORMAL

Downstream

TDP-43-Dependent Cryptic Exon Misprocessing Nuclear depletion of TDP-43 removes repression of cryptic exons and cryptic splice-polyadenylation events in disease-relevant transcripts.

TDP-43-Driven Glycolytic Failure Cytoplasmic TDP-43 sequesters hexokinase 1, coupling the proteinopathy to a glycolytic-metabolic lesion in motor neurons.

Show evidence (3 references)

PMID:32799899 SUPPORT Other

"TDP-43 bridges the divide between sporadic and familial ALS and remains a dominant protein of interest to understand disease pathogenesis."

Review summarizes TDP-43 as the common pathological bridge between sporadic and familial ALS mechanisms.

PMID:32799899 SUPPORT Human Clinical

"TDP-43 was identified as a primary component of ubiquitinated and hyper-phosphorylated cytosolic aggregates observed from post-mortem tissue of patients with ALS"

Postmortem ALS evidence identifies TDP-43 as a primary component of ubiquitinated, hyperphosphorylated cytosolic aggregates.

PMID:32799899 SUPPORT Other

"Together, these data suggest that both loss- and gain-of-TDP-43 function mediated by nuclear-to-cytoplasmic mislocalization cause systemic cellular dysfunction in ALS."

Synthesis supports the coupled loss-of-function and gain-of-function framing of TDP-43 mislocalization.

TDP-43-Dependent Cryptic Exon Misprocessing

Loss of nuclear TDP-43 derepresses cryptic exons and cryptic splice-polyadenylation events in RNA targets relevant to ALS. STMN2 misprocessing lowers stathmin-2, compromising axonal outgrowth, axon regeneration, and lysosome trafficking in TDP-43-deficient human motor neurons. UNC13A cryptic exon inclusion links common ALS/FTD risk variants to loss of nuclear TDP-43 function and can deplete a synaptic protein. This node represents the most concrete RNA-processing defect currently modeled as a candidate causal bridge from TDP-43 dysfunction toward motor-neuron death, while acknowledging that target priority and cell-type selectivity remain unresolved.

TDP-43 RNA Dysregulation and Motor-Neuron Selective Vulnerability Model

motor neuron CL:0000100

STMN2 hgnc:10577 UNC13A hgnc:23150

RNA splicing GO:0008380 ⚠ ABNORMAL nuclear-transcribed mRNA catabolic process, nonsense-mediated decay GO:0000184 ↑ INCREASED

Downstream

Axonal Transport Dysfunction STMN2 loss and related RNA misprocessing can impair axonal outgrowth, axon regeneration, and lysosome trafficking in human motor-neuron models.

Motor Neuron Degeneration Cryptic-exon misprocessing is modeled as an indirect, target-specific bridge from TDP-43 nuclear loss to motor-neuron degeneration through STMN2-dependent axonal repair defects, UNC13A-dependent synaptic defects, and other transcript-specific losses.

Show evidence (3 references)

PMID:26250685 SUPPORT In Vitro

"When TDP-43 was depleted from mouse embryonic stem cells, these cryptic exons were spliced into messenger RNAs, often disrupting their translation and promoting nonsense-mediated decay."

Demonstrates the basic cryptic-exon and nonsense-mediated decay mechanism caused by TDP-43 depletion.

PMID:36927019 SUPPORT In Vitro

"TDP-43 mislocalization results in cryptic splicing and polyadenylation of pre-messenger RNAs (pre-mRNAs) encoding stathmin-2 (also known as SCG10), a protein that is required for axonal regeneration."

Identifies STMN2 cryptic splice-polyadenylation as a direct consequence of TDP-43 mislocalization relevant to axonal regeneration.

PMID:35197626 SUPPORT Human Clinical

"Loss of TDP-43 from the nucleus in human brain, neuronal cell lines and motor neurons derived from induced pluripotent stem cells resulted in the inclusion of a cryptic exon in UNC13A mRNA and reduced UNC13A protein expression."

Establishes UNC13A cryptic exon inclusion and reduced protein expression after loss of nuclear TDP-43 in human brain and motor-neuron models.

C9orf72 Repeat Expansion Toxicity

Hexanucleotide (GGGGCC) repeat expansion in C9orf72 is the most common genetic cause of ALS, accounting for 40% of familial and 5-10% of sporadic cases. The expansion leads to RNA foci formation, dipeptide repeat protein aggregation, and haploinsufficiency.

C9orf72 hgnc:28337

Show evidence (3 references)

PMID:21944778 SUPPORT

"Analysis of extended clinical series found the C9ORF72 repeat expansion to be the most common genetic abnormality in both familial FTD (11.7%) and familial ALS (23.5%). The repeat expansion leads to the loss of one alternatively spliced C9ORF72 transcript and to formation of nuclear RNA foci,..."

Original discovery paper establishing C9orf72 repeat expansion as a major cause of both FTD and ALS with dual mechanisms.

PMID:22406228 SUPPORT Human Clinical

"The mutation was present in 217 (39·3%) of 552 white individuals with familial ALS from Europe and the USA."

Large cross-sectional study quantifies the C9orf72 expansion in ~40% of familial ALS in European/US populations, the source of the widely cited familial-ALS frequency and the strongest support for the node's ~40% figure.

PMID:37024676 SUPPORT

"Recent advances in sequencing technologies and collaborative efforts have led to substantial progress in identifying the genetic causes of amyotrophic lateral sclerosis (ALS). This momentum has, in turn, fostered the development of putative molecular therapies."

Review links expanding ALS genetic discoveries, including C9orf72, to the development of targeted molecular therapies.

Glutamate Excitotoxicity

Impaired glutamate clearance by astrocytes leads to excessive glutamate accumulation in the synaptic cleft, causing prolonged activation of glutamate receptors on motor neurons. This results in calcium overload and subsequent neuronal death.

astrocyte CL:0000127

neurotransmitter transport GO:0006836

Show evidence (2 references)

PMID:8302340 PARTIAL

"Some research suggests that the excitatory amino acid neurotransmitter glutamate may be involved in the pathogenesis."

Trial of riluzole, an antiglutamate agent, supports role of glutamate excitotoxicity in ALS pathogenesis.

PMID:40508048 SUPPORT

"understanding of the key pathogenetic links of ALS, including glutamate-mediated excitotoxicity and oxidative stress, has significantly advanced."

Recent mechanistic review highlights glutamate-mediated excitotoxicity as a key pathogenic process and therapeutic target in ALS.

Oxidative Stress

Motor neurons are particularly vulnerable to oxidative damage due to high metabolic demands. Mutations in SOD1, which encodes superoxide dismutase 1, lead to misfolded protein aggregation and increased oxidative stress contributing to neuronal death.

SOD1 hgnc:11179

response to oxidative stress GO:0006979

Show evidence (3 references)

PMID:8446170 SUPPORT

"a gene that encodes a cytosolic, Cu/Zn-binding superoxide dismutase (SOD1), a homodimeric metalloenzyme that catalyzes the dismutation of the toxic superoxide anion"

Discovery of SOD1 mutations in familial ALS implicates oxidative stress in disease pathogenesis.

PMID:40508048 SUPPORT

"This review considers the recent evidence on molecular mechanisms of these processes, as well as the therapeutic strategies aimed at their modulation. Special attention is paid to antiglutamatergic and antioxidant drugs as approaches to the ALS pathogenetic therapy."

Review emphasizes oxidative stress as a targetable pathogenic mechanism and discusses antioxidant therapeutic strategies in ALS.

PMID:35269543 SUPPORT

"ALS has a multifaceted nature affected by many pathological mechanisms, including oxidative stress (also via protein aggregation), mitochondrial dysfunction, glutamate-induced excitotoxicity, apoptosis, neuroinflammation, axonal degeneration, skeletal muscle deterioration and viruses."

Therapeutic strategies review highlights oxidative stress among key pathological mechanisms contributing to ALS.

Neuroinflammation

Activated microglia and astrocytes contribute to motor neuron death through the release of pro-inflammatory cytokines, reactive oxygen species, and other neurotoxic factors. This non-cell-autonomous mechanism amplifies neurodegeneration.

microglial cell CL:0000129 astrocyte CL:0000127

Show evidence (2 references)

PMID:34440810 PARTIAL

"In the archetypical neurodegenerative disorder amyotrophic lateral sclerosis (ALS), the recruitment of T-cells is well known"

Review confirms peripheral immune cell (T-cell) recruitment to the CNS in ALS; does not directly support the microglia/astrocyte cytokine/ROS mechanism described.

PMID:34874625 PARTIAL Human Clinical

"The involvement of nonmotor neuraxis emphasizes the contribution of glial cells in disease progress."

Review confirms that glial cells (microglia) contribute to ALS disease progression via non-cell-autonomous mechanisms; specific microglia/astrocyte cytokine/ROS citation still needed.

Microglial TREM2 Signaling

TREM2 expressed on microglia regulates proliferation, activation, and phagocytosis; altered TREM2 signaling is implicated in ALS progression through dysregulated microglial responses to motor neuron injury.

microglial cell CL:0000129

TREM2 hgnc:17761

microglial cell activation GO:0001774

Show evidence (1 reference)

PMID:34874625 SUPPORT

"Triggering receptor expressed on myeloid cell 2 (TREM2) is a surface receptor that, within the CNS, is exclusively expressed on microglia and plays crucial roles in microglial proliferation, migration, activation, metabolism, and phagocytosis."

Review summarizes how microglial TREM2 function shapes ALS progression and highlights its role in microglial activation.

Axonal Transport Dysfunction

Impaired axonal transport leads to accumulation of organelles and proteins in motor neuron axons, contributing to neurodegeneration. Gene mutations affecting cytoskeletal components (KIF5A, DCTN1, PFN1) contribute to this dysfunction.

KIF5A hgnc:6323 DCTN1 hgnc:2711 PFN1 hgnc:8881 NEFH hgnc:7737 PRPH hgnc:9461 ARHGEF28 hgnc:30322

anterograde axonal transport GO:0008089

Show evidence (1 reference)

PMID:22312314 PARTIAL

"Axonal transport defects are among the early molecular events leading to neurodegeneration in mouse models of amyotrophic lateral sclerosis (ALS)."

Review confirms axonal transport defects as early pathogenic events in ALS.

Impaired Autophagy

Defects in autophagy and protein quality control pathways lead to accumulation of misfolded proteins and damaged organelles in motor neurons. Multiple ALS genes (TBK1, OPTN, VCP, SQSTM1) function in autophagy.

TBK1 hgnc:11584 OPTN hgnc:17142 VCP hgnc:12666 SQSTM1 hgnc:11280

autophagy GO:0006914

Show evidence (1 reference)

PMID:28148298 SUPPORT

"TBK1 also has a major role in autophagy and mitophagy, chiefly the phosphorylation of autophagy adaptors. Several other ALS genes are also involved in autophagy, including p62 and OPTN."

Review describes TBK1's role in autophagy and confirms multiple ALS genes function in autophagy pathways.

TDP-43-Driven Glycolytic Failure

Cytoplasmic TDP-43 directly binds hexokinase 1 (HK1), the first rate-limiting enzyme of glycolysis, dissociating it from mitochondria and sequestering it into insoluble aggregates. The resulting loss of HK1 impairs glycolytic ATP production in motor neurons — a metabolic lesion observed consistently across TDP-43 mutant mice, patient-derived iPSC motor neurons, and ALS postmortem spinal cord. Compensating for HK1 loss reduces cytoplasmic TDP-43 and ubiquitin accumulation and improves motor performance and survival in models, marking a metabolic intervention point within the canonical proteostatic-failure framework.

motor neuron CL:0000100

HK1 hgnc:4922 TARDBP hgnc:11571

glycolytic process GO:0006096 ↓ DECREASED

Downstream

Motor Neuron Degeneration Loss of HK1-dependent glycolytic ATP production contributes to the bioenergetic failure of vulnerable motor neurons.

Show evidence (2 references)

PMID:41838122 SUPPORT In Vitro

"cytoplasmic TDP-43 directly disrupts glycolysis by targeting hexokinase 1 (HK1), the first rate-limiting enzyme of the pathway"

Identifies HK1 sequestration by cytoplasmic TDP-43 as a direct metabolic mechanism — a novel addition to the canonical proteostatic-failure model surfaced by the 2026 hypothesis-search report.

PMID:41838122 SUPPORT Human Clinical

"postmortem spinal cord tissue from ALS patients, we observe consistent decreases in HK1 protein level"

Consistent HK1 decreases in ALS postmortem spinal cord confirm the glycolytic lesion in human disease tissue.

Endogenous Retrovirus Reactivation and TDP-43 Feedback

Reactivation of endogenous retroviruses (ERVs), in particular human endogenous retrovirus type K (HERV-K/HML-2), and TDP-43 proteinopathy are mutually reinforcing. ERV expression is sufficient to stimulate cytoplasmic aggregation of TDP-43, and viral ERV transmission propagates TDP-43 pathology to recipient cells, providing a self-sustaining positive-feedback loop that can drive intercellular spread and disease progression. ERV transcripts are elevated in ALS brain, and this loop is the mechanistic rationale for repurposing antiretroviral therapy (e.g., Triumeq) in ALS.

motor neuron CL:0000100

inflammatory response GO:0006954 ↑ INCREASED

Downstream

TDP-43 Proteinopathy ERV (HERV-K) expression is sufficient to stimulate cytoplasmic TDP-43 aggregation, closing a feed-forward loop with TDP-43 proteinopathy.

Motor Neuron Degeneration Viral ERV transmission propagates TDP-43 pathology to recipient cells, providing a mechanism for intercellular spread of degeneration.

Show evidence (2 references)

PMID:36810738 SUPPORT Model Organism

"each sufficient to stimulate cytoplasmic aggregation of human TDP-43"

Drosophila and human-ERV experiments show ERV expression seeds cytoplasmic TDP-43 aggregation, the basis of the ERV-TDP-43 feedback loop.

PMID:37450244 SUPPORT Other

"human endogenous retrovirus type K (HERV-K), have been proposed to be involved in the propagation of neurodegeneration in ALS"

Review articulating the HERV-K/TDP-43 propagation model and its rationale as a target for antiretroviral therapy (Triumeq) in ALS.

⬡

Pathograph

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

●

Phenotypes

Digestive 1

Dysphagia FREQUENT Dysphagia HP:0002015

Show evidence (3 references)

ORPHA:803 SUPPORT

"HP:0002015 | Dysphagia | Frequent (79-30%)"

Orphanet lists dysphagia as frequent in ALS.

PMID:33085325 SUPPORT

"Bulbar dysfunction can manifest as dysphagia (trouble swallowing) and dysarthria (trouble speaking)."

StatPearls article highlights dysphagia as a common bulbar manifestation in ALS.

PMID:39207520 SUPPORT

"Throughout the disease, more than two-thirds of ALS patients experience dysphagia, regardless of the region of onset."

Dysphagia-focused review reports that swallowing difficulty affects the majority of ALS patients.

Head and Neck 2

Drooling FREQUENT Drooling HP:0002307

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0002307 | Drooling | Frequent (79-30%)"

Orphanet lists drooling as frequent in ALS.

PMID:34920148 SUPPORT

"The pooled prevalence of sialorrhea among ALS patients was 30.8% (95% CI: 20.0%-44.2%)."

Meta-analysis establishes pooled sialorrhea prevalence of 30.8% in ALS patients.

Xerostomia FREQUENT Xerostomia HP:0000217

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0000217 | Xerostomia | Frequent (79-30%)"

Orphanet lists xerostomia as frequent in ALS.

Musculoskeletal 6

Generalized Muscle Weakness OBLIGATE Generalized muscle weakness HP:0003324

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0003324 | Generalized muscle weakness | Very frequent (99-80%)"

Orphanet lists generalized muscle weakness as very frequent in ALS.

PMID:38891021 SUPPORT

"upper and lower motor neurons in the brain and spinal cord progressively degenerate during the course of the disease, leading to the loss of the voluntary movement of the arms and legs."

Review summarizes progressive motor neuron degeneration causing loss of voluntary movement.

Spasticity FREQUENT Spasticity HP:0001257

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0001257 | Spasticity | Frequent (79-30%)"

Orphanet lists spasticity as frequent in ALS.

PMID:33085325 SUPPORT

"Upper motor findings include spasticity, hyperactive reflexes, and a positive Babinski sign."

StatPearls article confirms spasticity as a cardinal upper motor neuron sign in ALS.

Respiratory Insufficiency FREQUENT Respiratory insufficiency due to muscle weakness HP:0002747

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0002878 | Respiratory failure | Frequent (79-30%)"

Orphanet lists respiratory failure (HP:0002878) as frequent; this entry uses the more specific HP:0002747 (respiratory insufficiency due to muscle weakness) which captures the neuromuscular etiology.

PMID:33085325 SUPPORT

"Death usually occurs within 2 to 5 years from respiratory failure."

Clinical overview states respiratory failure is the usual terminal event in ALS.

Skeletal Muscle Atrophy FREQUENT Skeletal muscle atrophy HP:0003202

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0003202 | Skeletal muscle atrophy | Frequent (79-30%)"

Orphanet lists skeletal muscle atrophy as frequent in ALS.

PMID:33085325 SUPPORT

"Lower motor neuron signs include muscle atrophy, weakness, flaccid paralysis, absent reflexes, fasciculations, and fibrillations."

Review details muscle atrophy as a key lower motor neuron sign in ALS.

Muscle Spasm FREQUENT Muscle spasm HP:0003394

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0003394 | Muscle spasm | Frequent (79-30%)"

Orphanet lists muscle spasm as frequent in ALS.

Spastic Paraparesis OCCASIONAL Spastic paraparesis HP:0002313

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0002313 | Spastic paraparesis | Occasional (29-5%)"

Orphanet lists spastic paraparesis as occasional in ALS.

Nervous System 9

Fasciculations FREQUENT Fasciculations HP:0002380

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0002380 | Fasciculations | Frequent (79-30%)"

Orphanet lists fasciculations as frequent in ALS.

PMID:27117334 SUPPORT

"In the LMN system, fasciculation potentials (FPs) are the earliest changes observed in affected muscles, a feature of LMN hyperexcitability."

Review confirms fasciculations are an early marker of lower motor neuron dysfunction in ALS.

Hyperreflexia FREQUENT Hyperreflexia HP:0001347

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0001347 | Hyperreflexia | Frequent (79-30%)"

Orphanet lists hyperreflexia as frequent in ALS.

PMID:33085325 SUPPORT

"Upper motor findings include spasticity, hyperactive reflexes, and a positive Babinski sign."

StatPearls review lists hyperactive reflexes as a core upper motor neuron finding in ALS.

Dysarthria FREQUENT Dysarthria HP:0001260

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0001260 | Dysarthria | Frequent (79-30%)"

Orphanet lists dysarthria as frequent in ALS.

PMID:33085325 SUPPORT

"Bulbar dysfunction can manifest as dysphagia (trouble swallowing) and dysarthria (trouble speaking)."

Review notes bulbar dysfunction in ALS commonly presents with dysarthria and dysphagia.

Paralysis FREQUENT Paralysis HP:0003470

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0003470 | Paralysis | Frequent (79-30%)"

Orphanet lists paralysis as frequent in ALS.

Depression FREQUENT Depression HP:0000716

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0000716 | Depression | Frequent (79-30%)"

Orphanet lists depression as frequent in ALS.

PMID:23466470 SUPPORT

"Symptoms of dysphagia, depression, cognitive impairment, difficulty with self-feeding and meal preparation, hypermetabolism, anxiety, respiratory insufficiency, and fatigue with meals increase the risk of malnutrition."

Nutrition review identifies depression as a contributing symptom in ALS.

Anxiety FREQUENT Anxiety HP:0000739

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0000739 | Anxiety | Frequent (79-30%)"

Orphanet lists anxiety as frequent in ALS.

PMID:23466470 SUPPORT

Nutrition review lists anxiety among symptoms contributing to malnutrition in ALS.

Atypical Behavior FREQUENT Atypical behavior HP:0000708

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0000708 | Atypical behavior | Frequent (79-30%)"

Orphanet lists atypical behavior as frequent in ALS.

PMID:33085325 SUPPORT

"Patients can also display changes in behavior due to frontotemporal dysfunction, and about 15% of patients develop frontotemporal dementia."

StatPearls review confirms behavioral changes from frontotemporal dysfunction in ALS patients.

Cognitive Impairment FREQUENT Cognitive impairment HP:0100543

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0100543 | Cognitive impairment | Frequent (79-30%)"

Orphanet lists cognitive impairment as frequent in ALS.

PMID:22305801 SUPPORT

"Cognitive impairment occurs in up to 50% of cases, and one in seven patients develops frank frontotemporal dementia (FTD)."

Population-based study reports cognitive impairment in up to 50% of ALS cases.

Sleep Disturbance OCCASIONAL Sleep disturbance HP:0002360

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0002360 | Sleep abnormality | Occasional (29-5%)"

Orphanet lists sleep disturbance as occasional in ALS.

Respiratory 2

Dyspnea FREQUENT Dyspnea HP:0002094

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0002094 | Dyspnea | Frequent (79-30%)"

Orphanet lists dyspnea as frequent in ALS.

Orthopnea OCCASIONAL Orthopnea HP:0012764

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0012764 | Orthopnea | Occasional (29-5%)"

Orphanet lists orthopnea as occasional in ALS.

Constitutional 2

Fatigue FREQUENT Fatigue HP:0012378

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0012378 | Fatigue | Frequent (79-30%)"

Orphanet lists fatigue as frequent in ALS.

PMID:23466470 SUPPORT

Nutrition review identifies fatigue as a contributing symptom to malnutrition risk in ALS.

Pain FREQUENT Pain HP:0012531

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0012531 | Pain | Frequent (79-30%)"

Orphanet lists pain as frequent in ALS.

PMID:33661072 SUPPORT

"Pooled prevalence of pain in ALS across all studies was 60% (95% CI = 50-69%), with a high degree of heterogeneity"

Systematic review and meta-analysis establishes pain prevalence of 60% across ALS populations.

Growth 1

Weight Loss FREQUENT Weight loss HP:0001824

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0001824 | Weight loss | Frequent (79-30%)"

Orphanet lists weight loss as frequent in ALS.

PMID:23466470 SUPPORT

"Amyotrophic lateral sclerosis (ALS) is a progressive neurological disease with high risk of malnutrition."

Nutrition review confirms ALS carries high risk of malnutrition and weight loss.

Other 23

Neurodegeneration OBLIGATE Neurodegeneration HP:0002180

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0002180 | Neurodegeneration | Very frequent (99-80%)"

Orphanet lists neurodegeneration as very frequent in ALS.

PMID:36116464 SUPPORT

"Amyotrophic lateral sclerosis is a fatal CNS neurodegenerative disease."

Lancet Seminar identifies ALS as a fatal CNS neurodegenerative disease.

Motor Neuron Atrophy VERY_FREQUENT Motor neuron atrophy HP:0007373

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0007373 | Motor neuron atrophy | Very frequent (99-80%)"

Orphanet lists motor neuron atrophy as very frequent in ALS.

Babinski Sign FREQUENT Babinski sign HP:0003487

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0003487 | Babinski sign | Frequent (79-30%)"

Orphanet lists Babinski sign as frequent in ALS.

PMID:33085325 SUPPORT

"Upper motor findings include spasticity, hyperactive reflexes, and a positive Babinski sign."

StatPearls review confirms positive Babinski sign as an upper motor neuron finding in ALS.

Hoffmann Sign FREQUENT Hoffmann sign HP:0031993

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0031993 | Hoffmann sign | Frequent (79-30%)"

Orphanet lists Hoffmann sign as frequent in ALS.

Dysphonia FREQUENT Dysphonia HP:0001618

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0001618 | Dysphonia | Frequent (79-30%)"

Orphanet lists dysphonia as frequent in ALS.

Fatigable Weakness of Bulbar Muscles FREQUENT Fatigable weakness of bulbar muscles HP:0030192

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0030192 | Fatigable weakness of bulbar muscles | Frequent (79-30%)"

Orphanet lists fatigable weakness of bulbar muscles as frequent in ALS.

Fatigable Weakness of Swallowing Muscles FREQUENT Fatigable weakness of swallowing muscles HP:0030195

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0030195 | Fatigable weakness of swallowing muscles | Frequent (79-30%)"

Orphanet lists fatigable weakness of swallowing muscles as frequent in ALS.

Fatigable Weakness of Respiratory Muscles FREQUENT Fatigable weakness of respiratory muscles HP:0030196

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0030196 | Fatigable weakness of respiratory muscles | Frequent (79-30%)"

Orphanet lists fatigable weakness of respiratory muscles as frequent in ALS.

Abnormality on Pulmonary Function Testing FREQUENT Abnormality on pulmonary function testing HP:0030878

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0030878 | Abnormality on pulmonary function testing | Frequent (79-30%)"

Orphanet lists abnormality on pulmonary function testing as frequent in ALS.

Distal Amyotrophy FREQUENT Distal amyotrophy HP:0003693

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0003693 | Distal amyotrophy | Frequent (79-30%)"

Orphanet lists distal amyotrophy as frequent in ALS.

Progressive Distal Muscular Atrophy FREQUENT Progressive distal muscular atrophy HP:0008955

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0008955 | Progressive distal muscular atrophy | Frequent (79-30%)"

Orphanet lists progressive distal muscular atrophy as frequent in ALS.

Upper Limb Muscle Weakness FREQUENT Upper limb muscle weakness HP:0003484

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0003484 | Upper limb muscle weakness | Frequent (79-30%)"

Orphanet lists upper limb muscle weakness as frequent in ALS.

PMID:33085325 SUPPORT

"the majority of the patients present with asymmetric limb weakness (80%) or bulbar dysfunction (20%)."

StatPearls review confirms asymmetric limb weakness as the most common presentation.

Lower Limb Muscle Weakness FREQUENT Lower limb muscle weakness HP:0007340

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0007340 | Lower limb muscle weakness | Frequent (79-30%)"

Orphanet lists lower limb muscle weakness as frequent in ALS.

Tongue Fasciculations OCCASIONAL Tongue fasciculations HP:0001308

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0001308 | Tongue fasciculations | Occasional (29-5%)"

Orphanet lists tongue fasciculations as occasional in ALS.

Tongue Atrophy FREQUENT Tongue atrophy HP:0012473

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0012473 | Tongue atrophy | Frequent (79-30%)"

Orphanet lists tongue atrophy as frequent in ALS.

Foot Dorsiflexor Weakness OCCASIONAL Foot dorsiflexor weakness HP:0009027

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0009027 | Foot dorsiflexor weakness | Occasional (29-5%)"

Orphanet lists foot dorsiflexor weakness as occasional in ALS.

Steppage Gait OCCASIONAL Steppage gait HP:0003376

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0003376 | Steppage gait | Occasional (29-5%)"

Orphanet lists steppage gait as occasional in ALS.

Cachexia OCCASIONAL Cachexia HP:0004326

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0004326 | Cachexia | Occasional (29-5%)"

Orphanet lists cachexia as occasional in ALS.

Emotional Lability FREQUENT Emotional lability HP:0000712

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0000712 | Emotional lability | Frequent (79-30%)"

Orphanet lists emotional lability as frequent in ALS.

PMID:33085325 SUPPORT

"Some patients may also present with Pseudobulbar affect, which is dysregulation of emotional responses exhibited by excessive laughter or crying."

StatPearls review describes pseudobulbar affect as dysregulated emotional responses in ALS patients.

Frontotemporal Dementia OCCASIONAL Frontotemporal dementia HP:0002145

Show evidence (3 references)

ORPHA:803 SUPPORT

"HP:0002145 | Frontotemporal dementia | Occasional (29-5%)"

Orphanet lists frontotemporal dementia as occasional in ALS.

PMID:33085325 SUPPORT

"about 15% of patients develop frontotemporal dementia."

StatPearls review reports approximately 15% of ALS patients develop frontotemporal dementia.

PMID:38802173 SUPPORT

"ALS forms a clinical continuum with frontotemporal dementia (FTD), in which there are progressive language deficits or behavioral changes."

Review describes ALS-FTD clinical continuum with overlapping genetics and pathology.

Language Impairment OCCASIONAL Language impairment HP:0002463

Show evidence (2 references)

ORPHA:803 SUPPORT

"HP:0002463 | Language impairment | Occasional (29-5%)"

Orphanet lists language impairment as occasional in ALS.

PMID:38802173 SUPPORT

"ALS forms a clinical continuum with frontotemporal dementia (FTD), in which there are progressive language deficits or behavioral changes."

ALS clinical features review describes progressive language deficits within the ALS-FTD spectrum.

Jaw Hyperreflexia OCCASIONAL Jaw hyperreflexia HP:0033683

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0033683 | Jaw hyperreflexia | Occasional (29-5%)"

Orphanet lists jaw hyperreflexia as occasional in ALS.

Laryngospasm VERY_RARE Laryngospasm HP:0025425

Show evidence (1 reference)

ORPHA:803 SUPPORT

"HP:0025425 | Laryngospasm | Very rare (<4-1%)"

Orphanet lists laryngospasm as very rare in ALS.

🧬

Genetic Associations

C9orf72 Repeat Expansion (Causative)

Autosomal Dominant

Show evidence (4 references)

ORPHA:803 SUPPORT

"C9ORF72 | C9orf72-SMCR8 complex subunit | hgnc:28337 | Disease-causing germline mutation(s) in"

Orphanet lists C9ORF72 as harboring disease-causing germline mutations in ALS.

PMID:21944778 SUPPORT

"Analysis of extended clinical series found the C9ORF72 repeat expansion to be the most common genetic abnormality in both familial FTD (11.7%) and familial ALS (23.5%)"

Original discovery paper establishing C9orf72 as the most common genetic cause of familial ALS.

PMID:22406228 SUPPORT Human Clinical

"This genetic lesion accounted for a large proportion (∼40·0%) of familial cases of ALS and FTD."

Cross-sectional study's headline conclusion supports the ~40% familial figure cited in this entry's notes.

+ 1 more reference

SOD1 Mutations (Causative)

Autosomal Dominant

Show evidence (2 references)

ORPHA:803 SUPPORT

"SOD1 | superoxide dismutase 1 | hgnc:11179 | Disease-causing germline mutation(s) in"

Orphanet lists SOD1 as harboring disease-causing germline mutations in ALS.

PMID:8446170 SUPPORT

"We identified 11 different SOD1 missense mutations in 13 different FALS families."

Original discovery paper identifying SOD1 mutations as a cause of familial ALS.

TARDBP Mutations (Causative)

Autosomal Dominant

Show evidence (2 references)

ORPHA:803 SUPPORT

"TARDBP | TAR DNA binding protein | hgnc:11571 | Disease-causing germline mutation(s) in"

Orphanet lists TARDBP as harboring disease-causing germline mutations in ALS.

PMID:35805149 SUPPORT

"Mutations in C9orf72, SOD1, TAR DNA binding protein 43 (TARDBP), and fused in sarcoma (FUS) genes are the four most common ones."

Gene therapy review highlights TARDBP among the most common ALS genes targeted by therapeutic strategies.

FUS Mutations (Causative)

Autosomal Dominant

Show evidence (2 references)

ORPHA:803 SUPPORT

"FUS | FUS RNA binding protein | hgnc:4010 | Disease-causing germline mutation(s) in"

Orphanet lists FUS as harboring disease-causing germline mutations in ALS.

PMID:35805149 SUPPORT

"Mutations in C9orf72, SOD1, TAR DNA binding protein 43 (TARDBP), and fused in sarcoma (FUS) genes are the four most common ones."

Review notes FUS among the four most common ALS genes and discusses gene-targeted therapies.

NEK1 Variants (Susceptibility)

Show evidence (2 references)

ORPHA:803 SUPPORT

"NEK1 | NIMA related kinase 1 | hgnc:7744 | Major susceptibility factor in"

Orphanet lists NEK1 as a major susceptibility factor in ALS.

PMID:27455347 SUPPORT

"In total, we observed NEK1 risk variants in nearly 3% of ALS cases. NEK1 has been linked to several cellular functions, including cilia formation, DNA-damage response, microtubule stability, neuronal morphology and axonal polarity."

Large-scale genetic study identifying NEK1 variants as risk factors for ALS.

ATXN2 Intermediate-Length Repeat Expansion (Susceptibility)

Gene: ATXN2 hgnc:10555

Show evidence (1 reference)

PMID:20740007 SUPPORT Human Clinical

"We found that intermediate-length polyQ expansions (27-33 glutamines) in ATXN2 were significantly associated with ALS. These data establish ATXN2 as a relatively common ALS susceptibility gene."

Landmark study analyzing the ATXN2 polyQ repeat in 915 ALS patients establishes intermediate-length expansions as a common ALS susceptibility factor and identifies ATXN2 as a modifier of TDP-43 toxicity.

ARHGEF28 (Pathogenic Variants)

Gene: ARHGEF28 hgnc:30322

Show evidence (1 reference)

CGGV:assertion_ac27cecc-9749-4c69-88fa-fe83b2d49568-2024-03-28T190000.000Z SUPPORT Other

ClinGen classifies the ARHGEF28-amyotrophic lateral sclerosis gene-disease relationship as limited with semidominant inheritance.

ARPP21 (Pathogenic Variants)

Gene: ARPP21 hgnc:16968

Show evidence (1 reference)

CGGV:assertion_02d4089a-94dd-42b6-ab09-dc258db00ae9-2025-01-14T200000.000Z SUPPORT Other

ClinGen classifies the ARPP21-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

CAV1 (Pathogenic Variants)

Gene: CAV1 hgnc:1527

Show evidence (1 reference)

CGGV:assertion_cab41529-d295-466c-8821-75a16bb12c38-2023-12-21T170000.000Z SUPPORT Other

ClinGen classifies the CAV1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

CAV2 (Pathogenic Variants)

Gene: CAV2 hgnc:1528

Show evidence (1 reference)

CGGV:assertion_38faae4c-13ae-4c28-bea4-43e3ad15e178-2023-12-21T170000.000Z SUPPORT Other

ClinGen classifies the CAV2-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

CFAP410 (Pathogenic Variants)

Gene: CFAP410 hgnc:1260

Show evidence (1 reference)

CGGV:assertion_bde7edf1-ccfa-443e-a917-cf3d2dd9cba6-2023-12-12T180000.000Z SUPPORT Other

ClinGen classifies the CFAP410-amyotrophic lateral sclerosis gene-disease relationship as limited with semidominant inheritance.

DCTN1 (Pathogenic Variants)

Gene: DCTN1 hgnc:2711

Show evidence (1 reference)

CGGV:assertion_5cd19f2c-2499-417f-94c8-2bd4bedf34ef-2023-08-04T160000.000Z SUPPORT Other

ClinGen classifies the DCTN1-amyotrophic lateral sclerosis gene-disease relationship as moderate with autosomal dominant inheritance.

DNAJC7 (Pathogenic Variants)

Gene: DNAJC7 hgnc:12392

Show evidence (1 reference)

CGGV:assertion_e2a12a19-b37a-4654-87fa-3a921c202c87-2022-10-27T160000.000Z SUPPORT Other

ClinGen classifies the DNAJC7-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

GLE1 (Pathogenic Variants)

Gene: GLE1 hgnc:4315

Show evidence (1 reference)

CGGV:assertion_0284b3cd-38af-4309-8ce4-054a0379e693-2023-10-10T160000.000Z SUPPORT Other

ClinGen classifies the GLE1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

GLT8D1 (Pathogenic Variants)

Gene: GLT8D1 hgnc:24870

Show evidence (1 reference)

CGGV:assertion_a2c4f919-ccb5-4d9f-a604-5ed19e19057e-2025-01-14T200000.000Z SUPPORT Other

ClinGen classifies the GLT8D1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

LGALSL (Pathogenic Variants)

Gene: LGALSL hgnc:25012

Show evidence (1 reference)

CGGV:assertion_5a2db59f-5293-4e5d-ae34-5a38d8c6ebdf-2023-02-14T170000.000Z SUPPORT Other

ClinGen classifies the LGALSL-amyotrophic lateral sclerosis gene-disease relationship as limited with undetermined inheritance.

NEFH (Pathogenic Variants)

Gene: NEFH hgnc:7737

Show evidence (1 reference)

CGGV:assertion_6c71deac-6b11-4947-8834-8391d516a9c9-2023-03-23T160000.000Z SUPPORT Other

ClinGen classifies the NEFH-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

NUP50 (Pathogenic Variants)

Gene: NUP50 hgnc:8065

Show evidence (1 reference)

CGGV:assertion_0ce3418e-c7e5-452b-9db6-661571331822-2024-06-27T160000.000Z SUPPORT Other

ClinGen classifies the NUP50-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

PRPH (Pathogenic Variants)

Gene: PRPH hgnc:9461

Show evidence (1 reference)

CGGV:assertion_3d11b04d-508a-4f91-9d9a-b5016fd0b940-2022-12-13T170000.000Z SUPPORT Other

ClinGen classifies the PRPH-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

SPTLC2 (Pathogenic Variants)

Gene: SPTLC2 hgnc:11278

Show evidence (1 reference)

CGGV:assertion_402cf65d-02f1-4cc1-a45e-b3bd3ad48b86-2024-06-26T160000.000Z SUPPORT Other

ClinGen classifies the SPTLC2-amyotrophic lateral sclerosis gene-disease relationship as strong with autosomal dominant inheritance.

SS18L1 (Pathogenic Variants)

Gene: SS18L1 hgnc:15592

Show evidence (1 reference)

CGGV:assertion_6e148a06-50fc-45f3-90ea-023dc8687577-2023-05-25T160000.000Z SUPPORT Other

ClinGen classifies the SS18L1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

TAF15 (Pathogenic Variants)

Gene: TAF15 hgnc:11547

Show evidence (1 reference)

CGGV:assertion_605446ae-fd1f-4451-bd49-643c24cd652e-2021-11-03T020945.214Z SUPPORT Other

ClinGen classifies the TAF15-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.

💊

Medical Actions

Riluzole

Action: Pharmacotherapy NCIT:C15986

Agent: riluzole NCIT:C47704

Glutamate antagonist that modestly extends survival by 2-3 months. It is the first FDA-approved treatment for ALS and works by reducing excitotoxic neuronal damage.

Mechanism Target:

INHIBITS Glutamate Excitotoxicity — Riluzole blocks voltage-gated sodium channels and reduces glutamate release at presynaptic terminals, attenuating excitotoxic motor neuron injury.

Show evidence (1 reference)

PMID:8302340 SUPPORT

"The antiglutamate agent riluzole appears to slow the progression of amyotrophic lateral sclerosis, and it may improve survival in patients with disease of bulbar onset."

Landmark trial demonstrating riluzole's survival benefit in ALS patients.

Edaravone

Action: Pharmacotherapy NCIT:C15986

Agent: edaravone CHEBI:31530

Antioxidant that may slow functional decline in a subset of ALS patients. It reduces oxidative stress and has shown benefit in early-stage patients.

Mechanism Target:

INHIBITS Oxidative Stress — Edaravone is a free-radical scavenger that neutralizes reactive oxygen species, reducing oxidative neuronal injury in motor neurons.

Show evidence (2 references)

PMID:28522181 SUPPORT

"Edaravone showed efficacy in a small subset of people with ALS who met criteria identified in post-hoc analysis of a previous phase 3 study, showing a significantly smaller decline of ALSFRS-R score compared with placebo."

Phase 3 trial demonstrating edaravone slows functional decline in early-stage ALS patients.

PMID:35006266 REFUTE

"although long-term intravenous edaravone therapy for patients with ALS was feasible and mainly well tolerated, it was not associated with any disease-modifying benefit."

Real-world cohort study found long-term intravenous edaravone well tolerated but without additional disease-modifying benefit versus standard therapy.

Tofersen

Action: Pharmacotherapy NCIT:C15986

Agent: tofersen NCIT:C166584

Antisense oligonucleotide therapy approved for SOD1-ALS that reduces SOD1 protein production, targeting the underlying genetic cause in this subset of patients.

Mechanism Target:

MODULATES Motor Neuron Degeneration — Tofersen reduces mutant SOD1 protein levels via RNase H-mediated mRNA knockdown, reducing the SOD1-driven oxidative and proteotoxic burden that accelerates motor neuron loss in SOD1-ALS.

Show evidence (3 references)

PMID:32640130 SUPPORT

"In adults with ALS due to SOD1 mutations, CSF SOD1 concentrations decreased at the highest concentration of tofersen administered intrathecally over a period of 12 weeks."

Phase 1-2 trial demonstrating tofersen reduces CSF SOD1 levels in SOD1-ALS patients.

PMID:36129998 SUPPORT

"The intrathecally administered antisense oligonucleotide tofersen reduces synthesis of the superoxide dismutase 1 (SOD1) protein and is being studied in patients with amyotrophic lateral sclerosis (ALS) associated with mutations in SOD1 (SOD1 ALS)."

VALOR pivotal phase 3 trial (the basis for tofersen's FDA approval) confirms the antisense mechanism reduces SOD1 protein synthesis in SOD1 ALS.

PMID:36543887 SUPPORT

"Significant discoveries and advances have been made in ALS preclinical models, genetics, pathology, biomarkers, imaging and clinical readouts over the last 10-15 years."

Translational review highlights recent advances enabling gene-targeted therapies like tofersen.

Jacifusen (ION363)

Action: Pharmacotherapy NCIT:C15986

Agent: ulefnersen NCIT:C188629

Investigational antisense oligonucleotide (ION363, also known as ulefnersen) that non-allele-specifically silences FUS to lower wild-type and mutant FUS protein, targeting the gain-of-function genetic cause in FUS-ALS. Delivered by serial intrathecal injection; evaluated in an expanded-access case series and an ongoing clinical trial.

Mechanism Target:

MODULATES Motor Neuron Degeneration — Jacifusen silences FUS expression via RNase H-mediated knockdown, reducing mutant FUS protein aggregation and toxicity in motor neurons and delaying neurodegeneration in FUS-ALS.

Show evidence (3 references)

PMID:40414239 SUPPORT Human Clinical

"Jacifusen is an antisense oligonucleotide targeting FUS pre-mRNA, previously shown to delay neurodegeneration in a mouse model and potentially slow functional decline in a first-in-human study."

Lancet expanded-access case series confirms jacifusen is an ASO targeting FUS pre-mRNA, supporting the FUS-knockdown mechanism of this treatment.

PMID:40414239 SUPPORT Human Clinical

"Biochemical and immunohistochemical analysis of CNS tissue samples from four participants showed reduced FUS protein levels and an apparent decrease in the burden of FUS pathology."

Post-mortem CNS analysis in treated patients demonstrates jacifusen lowers FUS protein and FUS-aggregate burden, the intended target-engagement readout in humans.

PMID:35075293 SUPPORT Model Organism

"ION363, a non-allele-specific FUS antisense oligonucleotide, efficiently silences Fus and reduces postnatal levels of FUS protein in the brain and spinal cord, delaying motor neuron degeneration."

Preclinical FUS knock-in mouse study establishes that ION363 silences Fus and delays motor neuron degeneration, the model-organism basis for the human program.

Triumeq

Action: Pharmacotherapy NCIT:C15986

Agent: abacavir/dolutegravir/lamivudine NCIT:C157543

Antiretroviral therapy (combination of dolutegravir, lamivudine, and abacavir) proposed for treating TDP-43-associated ALS through modulation of endogenous retroviruses. In preclinical models, Triumeq transiently and modestly improves early motor function without impacting overall disease progression, and reduces TDP-43-driven neuroinflammation via suppression of transcription factor ATF4 and inflammatory markers CXCL10 and IRF-1.

Mechanism Target:

INHIBITS Endogenous Retrovirus Reactivation and TDP-43 Feedback — Triumeq's antiretroviral components (the integrase inhibitor dolutegravir plus the reverse-transcriptase inhibitors abacavir and lamivudine) target the ERV (HERV-K) reactivation arm of the ERV-TDP-43 feedback loop.

INHIBITS Neuroinflammation — Triumeq suppresses TDP-43-driven inflammatory gene expression in the ALS neuroinflammation axis, including ATF4, CXCL10, and IRF-1.

Show evidence (1 reference)

PMID:42204279 SUPPORT Model Organism

"In this TDP-43 ALS mouse model, there was a positive association of TDP-43 mRNA levels with transcription factor ATF4, and inflammatory markers CXCL10 and IRF-1, and Triumeq treatment negated this association."

Triumeq negated TDP-43-associated inflammatory marker upregulation, linking the treatment to inhibition of the Neuroinflammation pathophysiology node.

Show evidence (2 references)

PMID:42204279 PARTIAL Model Organism

"Triumeq treatment significantly improved motor function early on in the disease course"

Preclinical study shows early motor function improvement in the TDP-43 ALS mouse model, but the abstract qualifies the effect as transient and modest with no impact on other progression markers or disease endpoint.

PMID:42204279 SUPPORT Model Organism

Triumeq modulates TDP-43-driven neuroinflammation by suppressing ATF4 and inflammatory cytokines in disease model.

Sodium Phenylbutyrate-Taurursodiol (AMX0035)

Action: Pharmacotherapy NCIT:C15986

Agent: sodium phenylbutyrate CHEBI:75316 tauroursodeoxycholic acid CHEBI:80774

Fixed-dose combination of sodium phenylbutyrate and taurursodiol (tauroursodeoxycholic acid) intended to reduce endoplasmic-reticulum and mitochondrial stress-mediated motor neuron death, marketed as Relyvrio (US) / Albrioza (Canada). The phase 2 CENTAUR trial showed slower functional decline, supporting accelerated FDA approval in 2022, but the confirmatory phase 3 PHOENIX trial showed no benefit at 48 weeks and the sponsor voluntarily withdrew the drug from the market in 2024. Included here to document a withdrawn ALS therapy whose disease-modifying benefit was not confirmed.

Show evidence (3 references)

PMID:32877582 SUPPORT Human Clinical

"the mean rate of change in the ALSFRS-R score was -1.24 points per month with the active drug and -1.66 points per month with placebo (difference, 0.42 points per month; 95% confidence interval, 0.03 to 0.81; P = 0.03)."

The phase 2 CENTAUR randomized controlled trial showed a statistically significant slowing of ALSFRS-R functional decline versus placebo — the result that supported the 2022 accelerated FDA approval.

PMID:38909349 REFUTE Human Clinical

"results from the Phase 3 PHOENIX trial (NCT05021536) showed no change in ALSFRS-R total score at 48 weeks."

The confirmatory phase 3 PHOENIX trial found no effect on the primary functional endpoint, refuting a disease-modifying benefit and reversing the CENTAUR signal.

PMID:38909349 REFUTE Human Clinical

"the sponsor company initiated the process with the US FDA and Health Canada to voluntarily withdraw the marketing authorizations for PB-TUDCA."

Following the negative PHOENIX trial, the sponsor voluntarily withdrew marketing authorizations in the US and Canada (2024), documenting the therapy's removal from clinical use.

Non-invasive Ventilation

Action: noninvasive ventilation Ontology label: Non-Invasive Mechanical Ventilation NCIT:C171457

Respiratory support using BiPAP or similar devices to assist breathing as respiratory muscles weaken. This improves quality of life and extends survival.

Show evidence (2 references)

PMID:16426990 SUPPORT

"This subgroup showed improvement in several measures of quality of life and a median survival benefit of 205 days (p=0.006) with maintained quality of life for most of this period."

Randomized controlled trial demonstrated non-invasive ventilation improves quality of life and extends survival in ALS patients with preserved bulbar function.

PMID:39019674 SUPPORT Human Clinical

"Non-invasive ventilation (NIV), which is the main recognized treatment for alleviating the symptoms of respiratory failure, prolongs survival and improves quality of life."

The French expert-panel respiratory-care guideline affirms non-invasive ventilation as the main recognized treatment for ALS respiratory failure, prolonging survival and improving quality of life.

Physical Therapy

Action: Physical Therapy NCIT:C15302

Range of motion exercises and adaptive strategies to maintain function and prevent complications such as contractures.

Show evidence (1 reference)

PMID:24510737 SUPPORT

"Multidisciplinary care includes rehabilitation interventions that have the goal of assisting people to teach their fullest potential despite the presence of a disabling disease."

Review describes how rehabilitation including physical therapy helps maximize independence and function in ALS patients.

Speech Therapy

Action: speech therapy Ontology label: Speech Language Therapy NCIT:C159273

Techniques to optimize communication and swallowing safety, including augmentative and alternative communication devices.

Show evidence (1 reference)

PMID:24510737 SUPPORT

"This review will present rehabilitation strategies that can be utilized to maximize patient independence, function, safety, and quality of life, and to minimize disease-related symptoms."

Review covers multidisciplinary rehabilitation including speech therapy for ALS patients.

Percutaneous Endoscopic Gastrostomy

Action: Percutaneous Endoscopic Gastrostomy NCIT:C106040

Feeding tube placement to maintain nutrition when swallowing becomes unsafe or inadequate due to bulbar involvement.

Show evidence (1 reference)

PMID:39207520 SUPPORT

"Early discussion of potential treatments such as high-calorie diets or percutaneous endoscopic gastrostomy (PEG) is crucial."

Dysphagia management review underscores PEG as an essential intervention when nutrition is compromised in ALS.

Multidisciplinary Care

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

Coordinated care from neurologists, pulmonologists, physical therapists, occupational therapists, speech therapists, nutritionists, and palliative care specialists extends survival and improves quality of life.

Show evidence (1 reference)

PMID:24510737 SUPPORT

"Multidisciplinary care includes rehabilitation interventions that have the goal of assisting people to teach their fullest potential despite the presence of a disabling disease."

Rehabilitation review emphasizes multidisciplinary care as core to ALS management to optimize function and quality of life.

🌍

Environmental Factors

Heavy Metal Exposure

Occupational and environmental exposure to lead, cadmium, mercury, and other heavy metals has been associated with increased ALS risk. Prospective pre-diagnostic blood-metal data (which minimize reverse causation) implicate cadmium and lead, with zinc inversely associated.

Show evidence (2 references)

PMID:31578652 SUPPORT Human Clinical

"The ratio of maximal/minimal lead exposure yielded a pooled odds ratio (OR) of 1.46 (95% confidence interval (CI) 1.16-1.83) with moderate heterogeneity (I2 = 51.8%; p = 0.019)."

Meta-analysis finds lead exposure positively associated with ALS risk across population-based studies.

PMID:33068316 SUPPORT Human Clinical

"cadmium and lead may be associated with an increased risk of ALS and zinc with a decreased risk. This is the first study to evaluate predisease metal levels in blood, thus minimizing reverse causation."

Nested case-control study in the prospective EPIC cohort measured pre-diagnostic blood metals, implicating cadmium and lead (and protective zinc) with a design that minimizes reverse causation. Identified as an un-integrated finding from the ALS environmental-toxicity deep-research report.

Pesticide Exposure

Agricultural pesticide exposure has been linked to increased ALS incidence in epidemiological studies.

Show evidence (1 reference)

PMID:22521219 SUPPORT

"In the meta-analysis, ALS was associated with use of pesticides as a group (1.9, 1.1-3.1)."

Systematic review and AHS cohort analysis report elevated ALS odds with pesticide exposure.

Military Service

Veterans have approximately twice the risk of developing ALS compared to the general population, possibly related to environmental exposures.

Show evidence (1 reference)

PMID:14504315 SUPPORT

"A significant elevated risk of ALS occurred among all deployed personnel (RR = 1.92; 95% CL = 1.29, 2.84)"

Gulf War veteran cohort showed nearly twofold higher ALS risk compared with non-deployed personnel.

Smoking

Cigarette smoking is the most consistently reported environmental ALS risk factor, though the overall association is modest; in this meta-analysis the clearest signal is a sex-specific increased risk in women (ever-smoker RR 1.66, 95% CI 1.31-2.10), while the overall pooled estimates were not statistically significant.

Show evidence (2 references)

PMID:20639382 PARTIAL Human Clinical

"The pooled RR (95% CI) of ALS was 1.28 (0.97 to 1.68) for current versus never smokers and 1.12 (0.98 to 1.27) for ever versus never smokers."

Meta-analysis of case-control and cohort studies found overall pooled relative risks that were elevated but not statistically significant (confidence intervals crossing 1.0), providing only partial support for smoking as an ALS risk factor.

PMID:20639382 SUPPORT Human Clinical

"was 0.86 (0.71 to 1.03) in men and 1.66 (1.31 to 2.10) in women."

Sex-stratified analysis shows a statistically significant elevated ALS risk in women who ever smoked (RR 1.66, 95% CI 1.31-2.10) but not in men, supporting the sex-specific smoking-ALS association.

Repetitive Head Trauma and Contact Sports

Repetitive concussive head and cervical-spinal trauma, particularly from professional contact sports (American football, soccer/association football, boxing), is associated with a markedly increased risk of ALS; head trauma is also an independent risk factor in broad risk-factor meta-analyses. The association overlaps the trauma-driven TDP-43 proteinopathy seen in chronic traumatic encephalopathy.

Show evidence (2 references)

PMID:30775214 SUPPORT Human Clinical

"repetitive concussive head and cervical spinal trauma result in an increased risk of ALS compared with the general population or nonsport controls."

Systematic review concludes that contact sports involving repetitive concussive head and cervical-spinal trauma increase ALS risk (with a pooled rate ratio of 8.52 for professional such sports). Identified as an un-integrated finding from the ALS environmental-toxicity deep-research report.

PMID:37284659 SUPPORT Human Clinical

"head trauma (OR = 1.26, 95% CI = 1.13, 1.40)"

Comprehensive observational meta-analysis identifies head trauma as an independent risk factor for ALS, corroborating the contact-sports signal.

🔬

Biochemical Markers

Neurofilament Light Chain (NfL) (Elevated)

Context: CSF and serum biomarker of axonal injury, elevated in ALS with prognostic value

Show evidence (2 references)

PMID:36543887 SUPPORT Other

"Plasma and cerebrospinal fluid (CSF) neurofilament protein levels look particularly promising and may improve the efficiency of future clinical trials and allow identification of responder subgroups."

Translational review identifies plasma and CSF neurofilament as the most promising ALS biomarkers for trial enrichment and responder identification.

PMID:36129998 SUPPORT Human Clinical

"Tofersen led to greater reductions in concentrations of SOD1 in CSF and of neurofilament light chains in plasma than placebo."

The VALOR phase 3 trial shows plasma neurofilament light chain falls with SOD1-lowering therapy, validating NfL as a pharmacodynamic biomarker of axonal injury that tracks treatment response in ALS.

Phosphorylated Neurofilament Heavy Chain (pNfH) (Elevated)

Context: CSF and serum biomarker of axonal injury

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from Amyotrophic Lateral Sclerosis:

Chronic Inflammatory Demyelinating Polyradiculoneuropathy MONDO:0006702

Overlapping Features Immune-mediated demyelinating neuropathy causing progressive symmetric weakness and sensory loss; may mimic lower motor neuron-predominant ALS.

Show evidence (1 reference)

PMID:33085325 SUPPORT

"Some disorders that can mimic motor neuron disease are multifocal motor neuropathy with conduction block, chronic inflammatory demyelinating polyradiculoneuropathy, central nervous system tumors, multiple sclerosis, and polyradiculopathy, among others."

StatPearls review lists CIDP among conditions that can mimic ALS and should be ruled out.

Multiple Sclerosis MONDO:0005301

Overlapping Features Demyelinating disease of the central nervous system with motor weakness and spasticity that can resemble early ALS presentations.

Show evidence (1 reference)

PMID:33085325 SUPPORT

The same review identifies multiple sclerosis as a diagnostic mimic of motor neuron disease.

Multifocal Motor Neuropathy Not Yet Curated MONDO:0018979

Overlapping Features Immune-mediated, asymmetric, distal motor neuropathy with conduction block that can present with focal weakness mimicking lower motor neuron ALS.

Show evidence (1 reference)

PMID:33085325 SUPPORT

StatPearls review lists multifocal motor neuropathy with conduction block as an ALS mimic that must be ruled out.

📊

Related Datasets

GTEx v8 Spinal Cord (cervical c-1) gtex:GTEx_v8_Spinal_cord_cervical_c-1

Bulk RNA-seq from healthy cervical spinal cord to provide baseline expression for upper and lower motor neuron pathways affected in ALS.

Homo sapiens BULK RNA SEQ

spinal cord

PMID:33085325

Show evidence (1 reference)

PMID:33085325 SUPPORT

"ALS is a neurodegenerative disorder leading to weakness of the bulbar, thoracic, limb, and abdominal muscles with sparing of sensory function."

Clinical overview notes degeneration across spinal motor systems; spinal cord baseline controls contextualize transcriptomic changes in ALS.

GTEx v8 Skeletal Muscle gtex:GTEx_v8_Skeletal_Muscle

Bulk RNA-seq from healthy skeletal muscle to benchmark ALS-related denervation signatures and muscle atrophy pathways.

Homo sapiens BULK RNA SEQ

skeletal muscle tissue

PMID:33085325

Show evidence (1 reference)

PMID:33085325 SUPPORT

"ALS is a neurodegenerative disorder leading to weakness of the bulbar, thoracic, limb, and abdominal muscles with sparing of sensory function."

Muscle weakness and atrophy are primary clinical consequences in ALS; healthy muscle RNA-seq provides comparative background for ALS muscle involvement.

{ }

Source YAML

click to show

name: Amyotrophic Lateral Sclerosis
creation_date: '2026-01-14T23:47:09Z'
category: Complex
description: >
  Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a progressive
  neurodegenerative disorder characterized by the selective death of upper and lower motor
  neurons in the brain, brainstem, and spinal cord. This leads to progressive muscle weakness,
  atrophy, spasticity, and ultimately respiratory failure. ALS typically presents in adulthood
  with a median survival of 3-5 years from symptom onset. Approximately 5-10% of cases are
  familial, with the remainder being sporadic. A hallmark feature is TDP-43 proteinopathy,
  present in approximately 97% of cases.
disease_term:
  preferred_term: amyotrophic lateral sclerosis
  term:
    id: MONDO:0004976
    label: amyotrophic lateral sclerosis
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
  mechanistic_category:
  - classification_value: proteotoxic disease
gene_sets:
- gene_set: MYGENESET:KEGG_AMYOTROPHIC_LATERAL_SCLEROSIS_ALS
  relationship: CANONICAL_PATHWAY
  note: >-
    KEGG amyotrophic lateral sclerosis pathway.
- gene_set: MYGENESET:WP_AMYOTROPHIC_LATERAL_SCLEROSIS_ALS
  relationship: CANONICAL_PATHWAY
  note: >-
    WikiPathways amyotrophic lateral sclerosis pathway.
parents:
- Motor Neuron Disease
- Neurodegenerative Disease
has_subtypes:
- name: Familial ALS
  description: Hereditary form of ALS accounting for 5-10% of cases, with mutations in genes such as SOD1, C9orf72, TARDBP, and FUS.
- name: Sporadic ALS
  description: Non-hereditary form of ALS accounting for 90-95% of cases with unclear etiology.
- name: Bulbar-onset ALS
  description: ALS beginning with speech and swallowing difficulties due to bulbar motor neuron involvement.
- name: Limb-onset ALS
  description: ALS beginning with limb weakness, the most common presentation.
mechanistic_hypotheses:
- hypothesis_group_id: canonical_motor_neuron_proteostatic_failure_model
  hypothesis_label: Canonical Motor Neuron Proteostatic Failure Model
  status: CANONICAL
  description: >-
    Progressive upper and lower motor neuron degeneration in ALS is the convergent endpoint of multiple genetic and sporadic insults that ultimately cause proteostatic failure. Key drivers include cytoplasmic mislocalization and aggregation of TDP-43 (in >97% of cases), C9orf72 hexanucleotide repeat expansion–derived dipeptide repeats and RNA foci, SOD1 misfolding, FUS/EWSR1 phase-separation defects, impaired autophagy, mitochondrial dysfunction, axonal transport failure, and neuroinflammation. Selective vulnerability of cortical layer-5 Betz cells and spinal alpha motor neurons leads to progressive muscle denervation, weakness, atrophy, and ultimately respiratory failure. Antisense-oligonucleotide therapy targeting SOD1 (tofersen) provides the strongest interventional validation of the SOD1 genetic-pathogenetic axis of this canonical multi-hit model; the C9orf72 ASO program (BIIB078) was discontinued after Phase 1 without clinical benefit, indicating that RNA-foci reduction alone is insufficient and DPR-mediated toxicity likely dominates the C9orf72 axis.
  notes: >-
    Retained as CANONICAL. The 2026 openscientist
    hypothesis-search report
    (kb/hypotheses/Amyotrophic_Lateral_Sclerosis/canonical_motor_neuron_proteostatic_failure_model)
    confirms convergent proteostatic failure as the unifying ALS
    mechanism: TDP-43 proteinopathy in ~97% of cases, SOD1 misfolding,
    C9orf72 RNA foci and DPRs, FUS phase-separation defects, impaired
    autophagy, mitochondrial dysfunction, axonal transport failure, and
    neuroinflammation all converge on motor-neuron degeneration. Tofersen
    (SOD1 ASO) approval provides the strongest causal validation of the
    genetic-pathogenetic axes. Three qualifications: (1) the C9orf72-ASO
    program (BIIB078; Phase 1 discontinued) showed insufficient clinical efficacy — RNA-foci
    reduction does not consistently translate to motor preservation,
    suggesting DPR-mediated toxicity may dominate; (2) the
    "proteostatic failure" framing remains a descriptive convergence
    rather than a single mechanistic primer — different genetic ALS
    subtypes follow different upstream paths; (3) sporadic ALS (~90%)
    requires environmental/epigenetic modifiers (BMAA, head trauma,
    aging) that the canonical model does not specify.
  evidence:
  - reference: PMID:38891021
    reference_title: "Updates on Disease Mechanisms and Therapeutics for Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "upper and lower motor neurons in the brain and spinal cord progressively degenerate"
    explanation: >
      Canonical mechanism review used as the seed reference for the
      hypothesis-search deep-research run.
  - reference: PMID:39986312
    reference_title: "Amyotrophic lateral sclerosis caused by hexanucleotide repeat expansions in C9orf72: from genetics to therapeutics."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical trials using antisense oligonucleotides to target the GGGGCC repeat RNA have not been successful, potentially because they only target a single gain-of-function mechanism."
    explanation: >
      Lancet Neurology 2025 review confirms that C9orf72 ASO trials did not
      achieve clinical benefit, directly qualifying the canonical model's
      genetic-pathogenetic-axis interventional validation. The hexanucleotide
      repeat expansion drives a complex interplay of loss-of-function and
      gain-of-function pathology that single-target therapies do not address.
- hypothesis_group_id: tdp43_rna_dysregulation_selective_vulnerability_model
  hypothesis_label: TDP-43 RNA Dysregulation and Motor-Neuron Selective Vulnerability Model
  status: EMERGING
  description: >-
    This focused model treats ALS-associated TDP-43 pathology as a coupled
    nuclear loss-of-function and cytoplasmic gain-of-function process. Nuclear
    depletion of TDP-43 removes cryptic-exon repression and other RNA-processing
    controls in vulnerable motor neurons, producing mis-spliced or unstable
    transcripts such as STMN2 and UNC13A that impair axonal repair, synaptic
    function, and proteostasis. Cytoplasmic TDP-43 aggregation may amplify injury
    through stress-granule and proteostatic dysfunction and may contribute to
    propagation, but the unresolved causal step is which RNA target, aggregate
    species, or non-cell-autonomous signal converts TDP-43 dysfunction into
    selective motor-neuron death.
  evidence:
  - reference: PMID:32799899
    reference_title: "The role of TDP-43 mislocalization in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Research has focused on the formation and consequences of cytosolic protein aggregates as drivers of ALS pathology through both gain- and loss-of-function mechanisms."
    explanation: >
      Review-level synthesis supports modeling TDP-43 pathology as both nuclear
      loss-of-function and cytoplasmic gain-of-function rather than as aggregation
      alone.
  - reference: PMID:26250685
    reference_title: "TDP-43 repression of nonconserved cryptic exons is compromised in ALS-FTD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "repression of cryptic exons was impaired in ALS-FTD cases, suggesting that this splicing defect could potentially underlie TDP-43 proteinopathy."
    explanation: >
      Human ALS-FTD tissue evidence links loss of TDP-43 cryptic-exon repression
      to TDP-43 proteinopathy.
  - reference: PMID:30643292
    reference_title: "ALS-implicated protein TDP-43 sustains levels of STMN2, a mediator of motor neuron growth and repair."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "STMN2 loss upon reduced TDP-43 function was due to altered splicing, which is functionally important, as we show STMN2 is necessary for normal axonal outgrowth and regeneration."
    explanation: >
      Human motor-neuron experiments identify STMN2 mis-splicing and loss as a
      functional downstream RNA target that impairs axonal growth and repair.
  - reference: PMID:35197628
    reference_title: "TDP-43 loss and ALS-risk SNPs drive mis-splicing and depletion of UNC13A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings, which demonstrate a genetic link between loss of nuclear TDP-43 function and disease, reveal the mechanism by which UNC13A variants exacerbate the effects of decreased TDP-43 function."
    explanation: >
      UNC13A cryptic splicing links a human ALS/FTD risk locus to loss of nuclear
      TDP-43 function, supporting a target-specific RNA-dysregulation arm of the
      focused hypothesis.
  notes: >-
    The 2026 OpenScientist hypothesis report
    (kb/hypotheses/Amyotrophic_Lateral_Sclerosis/tdp43_rna_dysregulation_selective_vulnerability_model)
    judged the TDP-43 loss-of-function/cryptic-exon arm to be the strongest,
    best-supported part of this hypothesis, while keeping the integrated model
    of RNA loss, cytoplasmic gain-of-function, selective vulnerability, and
    propagation as emerging because the rate-limiting RNA target, aggregate
    species, upstream trigger hierarchy, and spread mechanism remain unresolved.
    Additional report-suggested PMIDs were retained as curation leads and not
    added here without independent PubMed/cache verification.
pathophysiology:
- name: Motor Neuron Degeneration
  description: >
    Progressive death of upper motor neurons in the motor cortex and lower motor neurons
    in the brainstem and spinal cord leads to denervation of skeletal muscles. The loss of
    upper motor neurons causes spasticity and hyperreflexia, while lower motor neuron loss
    results in muscle weakness, atrophy, and fasciculations.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  locations:
  - preferred_term: primary motor cortex
    term:
      id: UBERON:0001384
      label: primary motor cortex
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "A neurodegenerative disease characterized by progressive muscular paralysis reflecting degeneration of motor neurons in the primary motor cortex, corticospinal tracts, brainstem and spinal cord."
    explanation: Orphanet definition confirms progressive motor neuron degeneration across cortex, brainstem, and spinal cord.
  - reference: PMID:38521060
    reference_title: "Single-cell dissection of the human motor and prefrontal cortices in ALS and FTLD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we identify known and previously unidentified vulnerable populations in cortical layer 5 and show that ALS- and FTLD-implicated motor and spindle neurons possess a virtually indistinguishable molecular identity."
    explanation: Single-cell atlas of human ALS motor cortex identifies vulnerable neuronal populations in cortical layer 5 (including ALS-implicated motor/spindle neurons), supporting selective cortical motor-neuron vulnerability.
  - reference: PMID:38891021
    reference_title: "Updates on Disease Mechanisms and Therapeutics for Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    snippet: "upper and lower motor neurons in the brain and spinal cord progressively degenerate during the course of the disease, leading to the loss of the voluntary movement of the arms and legs."
    explanation: Review summarizes canonical ALS pathology of progressive upper and lower motor neuron degeneration causing loss of voluntary movement.
  - reference: PMID:36116464
    reference_title: "Amyotrophic lateral sclerosis."
    supports: PARTIAL
    snippet: "Amyotrophic lateral sclerosis is a fatal CNS neurodegenerative disease."
    explanation: Lancet Seminar underscores ALS as a fatal neurodegenerative disorder affecting central nervous system motor pathways.
- name: Nuclear Pore Complex Dysfunction
  description: >
    Selective loss of nuclear pore complex (NPC) components, particularly the scaffold
    proteins NUP107 and NUP93 and FG-repeat-containing components, is a consistent feature
    across ALS postmortem spinal cord, SOD1^G93A and TDP-43 mutant mouse models, and human
    cell systems. CRISPR-mediated NUP107 depletion is sufficient to trigger cytoplasmic
    TDP-43 mislocalization, increased TDP-43 phosphorylation, and autophagy dysfunction,
    placing NPC dysfunction upstream of TDP-43 proteinopathy in the canonical proteostatic
    failure cascade. Oxidative stress exacerbates NPC subunit mislocalization, creating a
    redox-sensitive vulnerability that amplifies the downstream TDP-43 aggregation phenotype.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  genes:
  - preferred_term: NUP50
    term:
      id: hgnc:8065
      label: NUP50
  - preferred_term: GLE1
    term:
      id: hgnc:4315
      label: GLE1
  biological_processes:
  - preferred_term: nucleocytoplasmic transport
    term:
      id: GO:0006913
      label: nucleocytoplasmic transport
    modifier: DECREASED
  downstream:
  - target: TDP-43 Proteinopathy
    description: NPC scaffold loss permits cytoplasmic TDP-43 mislocalization, hyperphosphorylation, and autophagy dysfunction.
    evidence:
    - reference: PMID:40819564
      reference_title: "Nuclear pore complex dysfunction drives TDP-43 pathology in ALS."
      supports: SUPPORT
      snippet: "CRISPR-mediated depletion of NUP107 in human cells triggers hallmark features of ALS pathology, including cytoplasmic TDP-43 mislocalization, increased phosphorylation, and autophagy dysfunction."
      explanation: Direct CRISPR perturbation places NPC dysfunction upstream of TDP-43 proteinopathy.
  evidence:
  - reference: PMID:40819564
    reference_title: "Nuclear pore complex dysfunction drives TDP-43 pathology in ALS."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "CRISPR-mediated depletion of NUP107 in human cells triggers hallmark features of ALS pathology, including cytoplasmic TDP-43 mislocalization, increased phosphorylation, and autophagy dysfunction."
    explanation: >
      Direct CRISPR perturbation demonstrating that NPC dysfunction is sufficient to
      reproduce hallmark ALS molecular pathology, including TDP-43 cytoplasmic mislocalization,
      phosphorylation, and autophagy disruption. Establishes NPC dysfunction as an upstream
      driver of the canonical TDP-43 proteinopathy axis.
  - reference: PMID:40819564
    reference_title: "Nuclear pore complex dysfunction drives TDP-43 pathology in ALS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "selective loss of NPC components, particularly the scaffold proteins NUP107 and NUP93, and FG-repeat-containing components-is a consistent finding across ALS postmortem spinal cord"
    explanation: >
      Postmortem human ALS spinal cord shows selective NPC scaffold loss,
      confirming NPC dysfunction in human disease.
  - reference: PMID:40819564
    reference_title: "Nuclear pore complex dysfunction drives TDP-43 pathology in ALS."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "selective loss of NPC components, particularly the scaffold proteins NUP107 and NUP93, and FG-repeat-containing components-is a consistent finding across ALS postmortem spinal cord, SOD1^G93A and TDP-43 mutant mouse models, and human cell systems"
    explanation: >
      Convergent NPC dysfunction in SOD1^G93A and TDP-43 mutant mouse models
      confirms this finding is not a model-system artifact and supports
      cross-species generalizability of the mechanism.
- name: TDP-43 Proteinopathy
  conforms_to: "tdp43_proteinopathy#Cytoplasmic TDP-43 Aggregation"
  description: >
    Cytoplasmic aggregation of TDP-43 (TAR DNA-binding protein 43) is found in approximately
    97% of ALS cases, with notable exceptions such as SOD1- and FUS-associated ALS. TDP-43
    normally functions as a predominantly nuclear RNA-binding protein. In ALS it becomes
    depleted from the nucleus and accumulates in cytoplasmic phosphorylated, ubiquitinated
    inclusions, creating a coupled loss-of-nuclear-function and cytoplasmic gain-of-function
    state. The nuclear loss arm impairs RNA processing and cryptic-exon repression, while
    cytoplasmic aggregation may block normal cellular processes, disturb proteostasis, and
    participate in spread-like propagation.
  genes:
  - preferred_term: TARDBP
    term:
      id: hgnc:11571
      label: TARDBP
  biological_processes:
  - preferred_term: RNA processing
    term:
      id: GO:0006396
      label: RNA processing
    modifier: ABNORMAL
  - preferred_term: RNA splicing
    term:
      id: GO:0000375
      label: RNA splicing, via transesterification reactions
    modifier: ABNORMAL
  downstream:
  - target: TDP-43-Dependent Cryptic Exon Misprocessing
    description: >-
      Nuclear depletion of TDP-43 removes repression of cryptic exons and
      cryptic splice-polyadenylation events in disease-relevant transcripts.
    causal_link_type: DIRECT
    hypothesis_groups:
    - tdp43_rna_dysregulation_selective_vulnerability_model
    evidence:
    - reference: PMID:26250685
      reference_title: "TDP-43 repression of nonconserved cryptic exons is compromised in ALS-FTD."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "repression of cryptic exons was impaired in ALS-FTD cases, suggesting that this splicing defect could potentially underlie TDP-43 proteinopathy."
      explanation: >
        Human ALS-FTD tissue data place impaired cryptic-exon repression
        downstream of TDP-43 nuclear loss.
  - target: TDP-43-Driven Glycolytic Failure
    description: >-
      Cytoplasmic TDP-43 sequesters hexokinase 1, coupling the proteinopathy to a
      glycolytic-metabolic lesion in motor neurons.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41838122
      reference_title: "TDP-43 impairs glycolysis by sequestering hexokinase 1 in amyotrophic lateral sclerosis."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "cytoplasmic TDP-43 directly binds to HK1, disassociating it from mitochondria and promoting its sequestration"
      explanation: >-
        Cytoplasmic TDP-43 directly sequesters HK1 — the edge linking TDP-43
        proteinopathy to glycolytic failure.
  evidence:
  - reference: PMID:32799899
    reference_title: "The role of TDP-43 mislocalization in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "TDP-43 bridges the divide between sporadic and familial ALS and remains a dominant protein of interest to understand disease pathogenesis."
    explanation: >
      Review summarizes TDP-43 as the common pathological bridge between sporadic
      and familial ALS mechanisms.
  - reference: PMID:32799899
    reference_title: "The role of TDP-43 mislocalization in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TDP-43 was identified as a primary component of ubiquitinated and hyper-phosphorylated cytosolic aggregates observed from post-mortem tissue of patients with ALS"
    explanation: >
      Postmortem ALS evidence identifies TDP-43 as a primary component of
      ubiquitinated, hyperphosphorylated cytosolic aggregates.
  - reference: PMID:32799899
    reference_title: "The role of TDP-43 mislocalization in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Together, these data suggest that both loss- and gain-of-TDP-43 function mediated by nuclear-to-cytoplasmic mislocalization cause systemic cellular dysfunction in ALS."
    explanation: >
      Synthesis supports the coupled loss-of-function and gain-of-function
      framing of TDP-43 mislocalization.
- name: TDP-43-Dependent Cryptic Exon Misprocessing
  conforms_to: "tdp43_proteinopathy#Nuclear Loss of TDP-43 RNA-Processing Function"
  description: >
    Loss of nuclear TDP-43 derepresses cryptic exons and cryptic
    splice-polyadenylation events in RNA targets relevant to ALS. STMN2
    misprocessing lowers stathmin-2, compromising axonal outgrowth, axon
    regeneration, and lysosome trafficking in TDP-43-deficient human motor
    neurons. UNC13A cryptic exon inclusion links common ALS/FTD risk variants to
    loss of nuclear TDP-43 function and can deplete a synaptic protein. This
    node represents the most concrete RNA-processing defect currently modeled as
    a candidate causal bridge from TDP-43 dysfunction toward motor-neuron death,
    while acknowledging that target priority and cell-type selectivity remain
    unresolved.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  genes:
  - preferred_term: STMN2
    term:
      id: hgnc:10577
      label: STMN2
  - preferred_term: UNC13A
    term:
      id: hgnc:23150
      label: UNC13A
  biological_processes:
  - preferred_term: RNA splicing
    term:
      id: GO:0008380
      label: RNA splicing
    modifier: ABNORMAL
  - preferred_term: nuclear-transcribed mRNA catabolic process, nonsense-mediated decay
    term:
      id: GO:0000184
      label: nuclear-transcribed mRNA catabolic process, nonsense-mediated decay
    modifier: INCREASED
  downstream:
  - target: Axonal Transport Dysfunction
    description: >-
      STMN2 loss and related RNA misprocessing can impair axonal outgrowth,
      axon regeneration, and lysosome trafficking in human motor-neuron models.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - STMN2 depletion
    - impaired axonal regeneration
    - stathmin-2-dependent lysosome trafficking defects
    hypothesis_groups:
    - tdp43_rna_dysregulation_selective_vulnerability_model
    evidence:
    - reference: PMID:36927019
      reference_title: "Mechanism of STMN2 cryptic splice-polyadenylation and its correction for TDP-43 proteinopathies."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Targeting dCasRx or antisense oligonucleotides (ASOs) suppressed cryptic splicing, which restored axonal regeneration and stathmin-2-dependent lysosome trafficking in TDP-43-deficient human motor neurons."
      explanation: >
        Correcting STMN2 cryptic splicing restores axonal regeneration and
        lysosome trafficking in TDP-43-deficient human motor neurons, supporting
        an RNA-misprocessing-to-axon-dysfunction edge.
  - target: Motor Neuron Degeneration
    description: >-
      Cryptic-exon misprocessing is modeled as an indirect, target-specific
      bridge from TDP-43 nuclear loss to motor-neuron degeneration through
      STMN2-dependent axonal repair defects, UNC13A-dependent synaptic defects,
      and other transcript-specific losses.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - STMN2 depletion and impaired axonal repair
    - UNC13A nonsense-mediated decay and synaptic dysfunction
    - unresolved additional TDP-43 RNA targets
    hypothesis_groups:
    - tdp43_rna_dysregulation_selective_vulnerability_model
    evidence:
    - reference: PMID:30643292
      reference_title: "ALS-implicated protein TDP-43 sustains levels of STMN2, a mediator of motor neuron growth and repair."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "STMN2 loss upon reduced TDP-43 function was due to altered splicing, which is functionally important, as we show STMN2 is necessary for normal axonal outgrowth and regeneration."
      explanation: >
        STMN2 provides a functional motor-neuron target linking TDP-43 splicing
        loss to impaired axonal growth and repair.
    - reference: PMID:35197628
      reference_title: "TDP-43 loss and ALS-risk SNPs drive mis-splicing and depletion of UNC13A."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Two common intronic UNC13A polymorphisms strongly associated with amyotrophic lateral sclerosis and frontotemporal dementia risk overlap with TDP-43 binding sites."
      explanation: >
        UNC13A provides a human genetic-risk target whose cryptic exon is
        potentiated by TDP-43 loss, supporting a disease-relevant RNA target.
  evidence:
  - reference: PMID:26250685
    reference_title: "TDP-43 repression of nonconserved cryptic exons is compromised in ALS-FTD."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "When TDP-43 was depleted from mouse embryonic stem cells, these cryptic exons were spliced into messenger RNAs, often disrupting their translation and promoting nonsense-mediated decay."
    explanation: >
      Demonstrates the basic cryptic-exon and nonsense-mediated decay mechanism
      caused by TDP-43 depletion.
  - reference: PMID:36927019
    reference_title: "Mechanism of STMN2 cryptic splice-polyadenylation and its correction for TDP-43 proteinopathies."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "TDP-43 mislocalization results in cryptic splicing and polyadenylation of pre-messenger RNAs (pre-mRNAs) encoding stathmin-2 (also known as SCG10), a protein that is required for axonal regeneration."
    explanation: >
      Identifies STMN2 cryptic splice-polyadenylation as a direct consequence of
      TDP-43 mislocalization relevant to axonal regeneration.
  - reference: PMID:35197626
    reference_title: "TDP-43 represses cryptic exon inclusion in the FTD-ALS gene UNC13A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Loss of TDP-43 from the nucleus in human brain, neuronal cell lines and motor neurons derived from induced pluripotent stem cells resulted in the inclusion of a cryptic exon in UNC13A mRNA and reduced UNC13A protein expression."
    explanation: >
      Establishes UNC13A cryptic exon inclusion and reduced protein expression
      after loss of nuclear TDP-43 in human brain and motor-neuron models.
- name: C9orf72 Repeat Expansion Toxicity
  description: >
    Hexanucleotide (GGGGCC) repeat expansion in C9orf72 is the most common genetic cause
    of ALS, accounting for 40% of familial and 5-10% of sporadic cases. The expansion
    leads to RNA foci formation, dipeptide repeat protein aggregation, and haploinsufficiency.
  genes:
  - preferred_term: C9orf72
    term:
      id: hgnc:28337
      label: C9orf72
  evidence:
  - reference: PMID:21944778
    reference_title: "Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS."
    supports: SUPPORT
    snippet: "Analysis of extended clinical series found the C9ORF72 repeat expansion to be the most common genetic abnormality in both familial FTD (11.7%) and familial ALS (23.5%). The repeat expansion leads to the loss of one alternatively spliced C9ORF72 transcript and to formation of nuclear RNA foci, suggesting multiple disease mechanisms."
    explanation: Original discovery paper establishing C9orf72 repeat expansion as a major cause of both FTD and ALS with dual mechanisms.
  - reference: PMID:22406228
    reference_title: "Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mutation was present in 217 (39·3%) of 552 white individuals with familial ALS from Europe and the USA."
    explanation: Large cross-sectional study quantifies the C9orf72 expansion in ~40% of familial ALS in European/US populations, the source of the widely cited familial-ALS frequency and the strongest support for the node's ~40% figure.
  - reference: PMID:37024676
    reference_title: "Amyotrophic lateral sclerosis: translating genetic discoveries into therapies."
    supports: SUPPORT
    snippet: "Recent advances in sequencing technologies and collaborative efforts have led to substantial progress in identifying the genetic causes of amyotrophic lateral sclerosis (ALS). This momentum has, in turn, fostered the development of putative molecular therapies."
    explanation: Review links expanding ALS genetic discoveries, including C9orf72, to the development of targeted molecular therapies.
- name: Glutamate Excitotoxicity
  conforms_to: "glutamate_excitotoxicity#Excessive Glutamatergic Stimulation and Impaired Glutamate Clearance"
  description: >
    Impaired glutamate clearance by astrocytes leads to excessive glutamate accumulation
    in the synaptic cleft, causing prolonged activation of glutamate receptors on motor
    neurons. This results in calcium overload and subsequent neuronal death.
  cell_types:
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: neurotransmitter transport
    term:
      id: GO:0006836
      label: neurotransmitter transport
  evidence:
  - reference: PMID:8302340
    reference_title: "A controlled trial of riluzole in amyotrophic lateral sclerosis. ALS/Riluzole Study Group."
    supports: PARTIAL
    snippet: "Some research suggests that the excitatory amino acid neurotransmitter glutamate may be involved in the pathogenesis."
    explanation: Trial of riluzole, an antiglutamate agent, supports role of glutamate excitotoxicity in ALS pathogenesis.
  - reference: PMID:40508048
    reference_title: "Amyotrophic Lateral Sclerosis: Pathophysiological Mechanisms and Treatment Strategies (Part 2)."
    supports: SUPPORT
    snippet: "understanding of the key pathogenetic links of ALS, including glutamate-mediated excitotoxicity and oxidative stress, has significantly advanced."
    explanation: Recent mechanistic review highlights glutamate-mediated excitotoxicity as a key pathogenic process and therapeutic target in ALS.
- name: Oxidative Stress
  description: >
    Motor neurons are particularly vulnerable to oxidative damage due to high metabolic
    demands. Mutations in SOD1, which encodes superoxide dismutase 1, lead to misfolded
    protein aggregation and increased oxidative stress contributing to neuronal death.
  genes:
  - preferred_term: SOD1
    term:
      id: hgnc:11179
      label: SOD1
  biological_processes:
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
  evidence:
  - reference: PMID:8446170
    reference_title: "Mutations in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "a gene that encodes a cytosolic, Cu/Zn-binding superoxide dismutase (SOD1), a homodimeric metalloenzyme that catalyzes the dismutation of the toxic superoxide anion"
    explanation: Discovery of SOD1 mutations in familial ALS implicates oxidative stress in disease pathogenesis.
  - reference: PMID:40508048
    reference_title: "Amyotrophic Lateral Sclerosis: Pathophysiological Mechanisms and Treatment Strategies (Part 2)."
    supports: SUPPORT
    snippet: "This review considers the recent evidence on molecular mechanisms of these processes, as well as the therapeutic strategies aimed at their modulation. Special attention is paid to antiglutamatergic and antioxidant drugs as approaches to the ALS pathogenetic therapy."
    explanation: Review emphasizes oxidative stress as a targetable pathogenic mechanism and discusses antioxidant therapeutic strategies in ALS.
  - reference: PMID:35269543
    reference_title: "Comprehensive Research on Past and Future Therapeutic Strategies Devoted to Treatment of Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    snippet: "ALS has a multifaceted nature affected by many pathological mechanisms, including oxidative stress (also via protein aggregation), mitochondrial dysfunction, glutamate-induced excitotoxicity, apoptosis, neuroinflammation, axonal degeneration, skeletal muscle deterioration and viruses."
    explanation: Therapeutic strategies review highlights oxidative stress among key pathological mechanisms contributing to ALS.
- name: Neuroinflammation
  description: >
    Activated microglia and astrocytes contribute to motor neuron death through the release
    of pro-inflammatory cytokines, reactive oxygen species, and other neurotoxic factors.
    This non-cell-autonomous mechanism amplifies neurodegeneration.
  cell_types:
  - preferred_term: microglial cell
    term:
      id: CL:0000129
      label: microglial cell
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  evidence:
  - reference: PMID:34440810
    reference_title: "What Guides Peripheral Immune Cells into the Central Nervous System?"
    supports: PARTIAL
    snippet: "In the archetypical neurodegenerative disorder amyotrophic lateral sclerosis (ALS), the recruitment of T-cells is well known"
    explanation: Review confirms peripheral immune cell (T-cell) recruitment to the CNS in ALS; does not directly support the microglia/astrocyte cytokine/ROS mechanism described.
  - reference: PMID:34874625
    reference_title: "Microglial TREM2 in amyotrophic lateral sclerosis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "The involvement of nonmotor neuraxis emphasizes the contribution of glial cells in disease progress."
    explanation: Review confirms that glial cells (microglia) contribute to ALS disease progression via non-cell-autonomous mechanisms; specific microglia/astrocyte cytokine/ROS citation still needed.
- name: Microglial TREM2 Signaling
  description: >
    TREM2 expressed on microglia regulates proliferation, activation, and phagocytosis; altered
    TREM2 signaling is implicated in ALS progression through dysregulated microglial responses
    to motor neuron injury.
  cell_types:
  - preferred_term: microglial cell
    term:
      id: CL:0000129
      label: microglial cell
  genes:
  - preferred_term: TREM2
    term:
      id: hgnc:17761
      label: TREM2
  biological_processes:
  - preferred_term: microglial cell activation
    term:
      id: GO:0001774
      label: microglial cell activation
  evidence:
  - reference: PMID:34874625
    reference_title: "Microglial TREM2 in amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Triggering receptor expressed on myeloid cell 2 (TREM2) is a surface receptor that, within the CNS, is exclusively expressed on microglia and plays crucial roles in microglial proliferation, migration, activation, metabolism, and phagocytosis."
    explanation: Review summarizes how microglial TREM2 function shapes ALS progression and highlights its role in microglial activation.
- name: Axonal Transport Dysfunction
  description: >
    Impaired axonal transport leads to accumulation of organelles and proteins in motor
    neuron axons, contributing to neurodegeneration. Gene mutations affecting cytoskeletal
    components (KIF5A, DCTN1, PFN1) contribute to this dysfunction.
  genes:
  - preferred_term: KIF5A
    term:
      id: hgnc:6323
      label: KIF5A
  - preferred_term: DCTN1
    term:
      id: hgnc:2711
      label: DCTN1
  - preferred_term: PFN1
    term:
      id: hgnc:8881
      label: PFN1
  - preferred_term: NEFH
    term:
      id: hgnc:7737
      label: NEFH
  - preferred_term: PRPH
    term:
      id: hgnc:9461
      label: PRPH
  - preferred_term: ARHGEF28
    term:
      id: hgnc:30322
      label: ARHGEF28
  biological_processes:
  - preferred_term: anterograde axonal transport
    term:
      id: GO:0008089
      label: anterograde axonal transport
  evidence:
  - reference: PMID:22312314
    reference_title: "Disruption of axonal transport in motor neuron diseases."
    supports: PARTIAL
    snippet: "Axonal transport defects are among the early molecular events leading to neurodegeneration in mouse models of amyotrophic lateral sclerosis (ALS)."
    explanation: Review confirms axonal transport defects as early pathogenic events in ALS.
- name: Impaired Autophagy
  conforms_to: "disabled_macroautophagy#Failure of Cytoplasmic Quality Control"
  description: >
    Defects in autophagy and protein quality control pathways lead to accumulation of
    misfolded proteins and damaged organelles in motor neurons. Multiple ALS genes
    (TBK1, OPTN, VCP, SQSTM1) function in autophagy.
  genes:
  - preferred_term: TBK1
    term:
      id: hgnc:11584
      label: TBK1
  - preferred_term: OPTN
    term:
      id: hgnc:17142
      label: OPTN
  - preferred_term: VCP
    term:
      id: hgnc:12666
      label: VCP
  - preferred_term: SQSTM1
    term:
      id: hgnc:11280
      label: SQSTM1
  biological_processes:
  - preferred_term: autophagy
    term:
      id: GO:0006914
      label: autophagy
  evidence:
  - reference: PMID:28148298
    reference_title: "TBK1: a new player in ALS linking autophagy and neuroinflammation."
    supports: SUPPORT
    snippet: "TBK1 also has a major role in autophagy and mitophagy, chiefly the phosphorylation of autophagy adaptors. Several other ALS genes are also involved in autophagy, including p62 and OPTN."
    explanation: Review describes TBK1's role in autophagy and confirms multiple ALS genes function in autophagy pathways.
- name: TDP-43-Driven Glycolytic Failure
  description: >
    Cytoplasmic TDP-43 directly binds hexokinase 1 (HK1), the first rate-limiting
    enzyme of glycolysis, dissociating it from mitochondria and sequestering it
    into insoluble aggregates. The resulting loss of HK1 impairs glycolytic ATP
    production in motor neurons — a metabolic lesion observed consistently across
    TDP-43 mutant mice, patient-derived iPSC motor neurons, and ALS postmortem
    spinal cord. Compensating for HK1 loss reduces cytoplasmic TDP-43 and
    ubiquitin accumulation and improves motor performance and survival in models,
    marking a metabolic intervention point within the canonical proteostatic-failure
    framework.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  genes:
  - preferred_term: HK1
    term:
      id: hgnc:4922
      label: HK1
  - preferred_term: TARDBP
    term:
      id: hgnc:11571
      label: TARDBP
  biological_processes:
  - preferred_term: glycolytic process
    term:
      id: GO:0006096
      label: glycolytic process
    modifier: DECREASED
  downstream:
  - target: Motor Neuron Degeneration
    description: >-
      Loss of HK1-dependent glycolytic ATP production contributes to the
      bioenergetic failure of vulnerable motor neurons.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired glycolytic ATP production
    - motor neuron bioenergetic failure
    evidence:
    - reference: PMID:41838122
      reference_title: "TDP-43 impairs glycolysis by sequestering hexokinase 1 in amyotrophic lateral sclerosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "postmortem spinal cord tissue from ALS patients, we observe consistent decreases in HK1 protein level"
      explanation: >-
        Reduced HK1 in ALS patient spinal cord links the glycolytic lesion to
        human motor neuron degeneration.
    - reference: PMID:41838122
      reference_title: "TDP-43 impairs glycolysis by sequestering hexokinase 1 in amyotrophic lateral sclerosis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "compensation for HK1 loss reduces cytoplasmic TDP-43 and ubiquitin accumulation, improves motor performance, and prolongs survival"
      explanation: >-
        Restoring HK1 (glycolytic rescue) by AAV-HK1 overexpression in the motor
        cortex of TDP-43A315T mice reduces cytoplasmic TDP-43 and ubiquitin,
        improves motor performance, and prolongs survival — interventional
        confirmation that the HK1 glycolytic lesion contributes causally to the
        motor-neuron degeneration downstream of TDP-43 proteinopathy.
  evidence:
  - reference: PMID:41838122
    reference_title: "TDP-43 impairs glycolysis by sequestering hexokinase 1 in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "cytoplasmic TDP-43 directly disrupts glycolysis by targeting hexokinase 1 (HK1), the first rate-limiting enzyme of the pathway"
    explanation: >-
      Identifies HK1 sequestration by cytoplasmic TDP-43 as a direct metabolic
      mechanism — a novel addition to the canonical proteostatic-failure model
      surfaced by the 2026 hypothesis-search report.
  - reference: PMID:41838122
    reference_title: "TDP-43 impairs glycolysis by sequestering hexokinase 1 in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "postmortem spinal cord tissue from ALS patients, we observe consistent decreases in HK1 protein level"
    explanation: >-
      Consistent HK1 decreases in ALS postmortem spinal cord confirm the
      glycolytic lesion in human disease tissue.
- name: Endogenous Retrovirus Reactivation and TDP-43 Feedback
  description: >
    Reactivation of endogenous retroviruses (ERVs), in particular human
    endogenous retrovirus type K (HERV-K/HML-2), and TDP-43 proteinopathy are
    mutually reinforcing. ERV expression is sufficient to stimulate cytoplasmic
    aggregation of TDP-43, and viral ERV transmission propagates TDP-43 pathology
    to recipient cells, providing a self-sustaining positive-feedback loop that
    can drive intercellular spread and disease progression. ERV transcripts are
    elevated in ALS brain, and this loop is the mechanistic rationale for
    repurposing antiretroviral therapy (e.g., Triumeq) in ALS.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  downstream:
  - target: TDP-43 Proteinopathy
    description: >-
      ERV (HERV-K) expression is sufficient to stimulate cytoplasmic TDP-43
      aggregation, closing a feed-forward loop with TDP-43 proteinopathy.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:36810738
      reference_title: "Endogenous retroviruses and TDP-43 proteinopathy form a sustaining feedback driving intercellular spread of Drosophila neurodegeneration."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "each sufficient to stimulate cytoplasmic aggregation of human TDP-43"
      explanation: >-
        ERV expression is sufficient to seed cytoplasmic TDP-43 aggregation,
        establishing the ERV-to-TDP-43 arm of the feedback loop.
  - target: Motor Neuron Degeneration
    description: >-
      Viral ERV transmission propagates TDP-43 pathology to recipient cells,
      providing a mechanism for intercellular spread of degeneration.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - intercellular ERV transmission
    - templated TDP-43 pathology in recipient neurons
    evidence:
    - reference: PMID:36810738
      reference_title: "Endogenous retroviruses and TDP-43 proteinopathy form a sustaining feedback driving intercellular spread of Drosophila neurodegeneration."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Viral ERV transmission also triggers TDP-43 pathology in recipient cells"
      explanation: >-
        ERV transmission propagates TDP-43 pathology between cells, supporting an
        ERV-driven spread mechanism for disease progression.
  evidence:
  - reference: PMID:36810738
    reference_title: "Endogenous retroviruses and TDP-43 proteinopathy form a sustaining feedback driving intercellular spread of Drosophila neurodegeneration."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "each sufficient to stimulate cytoplasmic aggregation of human TDP-43"
    explanation: >-
      Drosophila and human-ERV experiments show ERV expression seeds cytoplasmic
      TDP-43 aggregation, the basis of the ERV-TDP-43 feedback loop.
  - reference: PMID:37450244
    reference_title: "The Molecular Link Between TDP-43, Endogenous Retroviruses and Inflammatory Neurodegeneration in Amyotrophic Lateral Sclerosis: a Potential Target for Triumeq, an Antiretroviral Therapy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "human endogenous retrovirus type K (HERV-K), have been proposed to be involved in the propagation of neurodegeneration in ALS"
    explanation: >-
      Review articulating the HERV-K/TDP-43 propagation model and its rationale
      as a target for antiretroviral therapy (Triumeq) in ALS.
phenotypes:
- name: Generalized Muscle Weakness
  category: Neuromuscular
  frequency: OBLIGATE
  diagnostic: true
  description: Progressive loss of voluntary muscle strength affecting limbs, trunk, and respiratory muscles.
  phenotype_term:
    preferred_term: Generalized muscle weakness
    term:
      id: HP:0003324
      label: Generalized muscle weakness
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003324 | Generalized muscle weakness | Very frequent (99-80%)"
    explanation: Orphanet lists generalized muscle weakness as very frequent in ALS.
  - reference: PMID:38891021
    reference_title: "Updates on Disease Mechanisms and Therapeutics for Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    snippet: "upper and lower motor neurons in the brain and spinal cord progressively degenerate during the course of the disease, leading to the loss of the voluntary movement of the arms and legs."
    explanation: Review summarizes progressive motor neuron degeneration causing loss of voluntary movement.
- name: Neurodegeneration
  category: Neurological
  frequency: OBLIGATE
  description: Progressive degeneration of upper and lower motor neurons, the hallmark of ALS.
  phenotype_term:
    preferred_term: Neurodegeneration
    term:
      id: HP:0002180
      label: Neurodegeneration
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002180 | Neurodegeneration | Very frequent (99-80%)"
    explanation: Orphanet lists neurodegeneration as very frequent in ALS.
  - reference: PMID:36116464
    reference_title: "Amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Amyotrophic lateral sclerosis is a fatal CNS neurodegenerative disease."
    explanation: Lancet Seminar identifies ALS as a fatal CNS neurodegenerative disease.
- name: Motor Neuron Atrophy
  category: Neurological
  frequency: VERY_FREQUENT
  description: Loss of motor neurons in cortex, brainstem, and spinal cord.
  phenotype_term:
    preferred_term: Motor neuron atrophy
    term:
      id: HP:0007373
      label: Motor neuron atrophy
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0007373 | Motor neuron atrophy | Very frequent (99-80%)"
    explanation: Orphanet lists motor neuron atrophy as very frequent in ALS.
- name: Fasciculations
  category: Neuromuscular
  frequency: FREQUENT
  diagnostic: true
  description: Visible involuntary muscle twitching resulting from spontaneous motor unit discharges.
  phenotype_term:
    preferred_term: Fasciculations
    term:
      id: HP:0002380
      label: Fasciculations
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002380 | Fasciculations | Frequent (79-30%)"
    explanation: Orphanet lists fasciculations as frequent in ALS.
  - reference: PMID:27117334
    reference_title: "Lower motor neuron dysfunction in ALS."
    supports: SUPPORT
    snippet: "In the LMN system, fasciculation potentials (FPs) are the earliest changes observed in affected muscles, a feature of LMN hyperexcitability."
    explanation: Review confirms fasciculations are an early marker of lower motor neuron dysfunction in ALS.
- name: Spasticity
  category: Neurological
  frequency: FREQUENT
  description: Increased muscle tone and stiffness due to upper motor neuron involvement.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0001257 | Spasticity | Frequent (79-30%)"
    explanation: Orphanet lists spasticity as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Upper motor findings include spasticity, hyperactive reflexes, and a positive Babinski sign."
    explanation: StatPearls article confirms spasticity as a cardinal upper motor neuron sign in ALS.
- name: Hyperreflexia
  category: Neurological
  frequency: FREQUENT
  description: Exaggerated deep tendon reflexes indicating upper motor neuron dysfunction.
  phenotype_term:
    preferred_term: Hyperreflexia
    term:
      id: HP:0001347
      label: Hyperreflexia
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0001347 | Hyperreflexia | Frequent (79-30%)"
    explanation: Orphanet lists hyperreflexia as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Upper motor findings include spasticity, hyperactive reflexes, and a positive Babinski sign."
    explanation: StatPearls review lists hyperactive reflexes as a core upper motor neuron finding in ALS.
- name: Babinski Sign
  category: Neurological
  frequency: FREQUENT
  diagnostic: true
  description: Extensor plantar response indicating upper motor neuron dysfunction.
  phenotype_term:
    preferred_term: Babinski sign
    term:
      id: HP:0003487
      label: Babinski sign
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003487 | Babinski sign | Frequent (79-30%)"
    explanation: Orphanet lists Babinski sign as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Upper motor findings include spasticity, hyperactive reflexes, and a positive Babinski sign."
    explanation: StatPearls review confirms positive Babinski sign as an upper motor neuron finding in ALS.
- name: Hoffmann Sign
  category: Neurological
  frequency: FREQUENT
  description: Pathological reflex of the hand indicating upper motor neuron dysfunction in the cervical cord.
  phenotype_term:
    preferred_term: Hoffmann sign
    term:
      id: HP:0031993
      label: Hoffmann sign
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0031993 | Hoffmann sign | Frequent (79-30%)"
    explanation: Orphanet lists Hoffmann sign as frequent in ALS.
- name: Dysarthria
  category: Neurological
  frequency: FREQUENT
  description: Difficulty with speech articulation due to weakness of bulbar muscles.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0001260 | Dysarthria | Frequent (79-30%)"
    explanation: Orphanet lists dysarthria as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Bulbar dysfunction can manifest as dysphagia (trouble swallowing) and dysarthria (trouble speaking)."
    explanation: Review notes bulbar dysfunction in ALS commonly presents with dysarthria and dysphagia.
- name: Dysphonia
  category: Neurological
  frequency: FREQUENT
  description: Voice changes and hoarseness due to weakness of laryngeal muscles.
  phenotype_term:
    preferred_term: Dysphonia
    term:
      id: HP:0001618
      label: Dysphonia
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0001618 | Dysphonia | Frequent (79-30%)"
    explanation: Orphanet lists dysphonia as frequent in ALS.
- name: Dysphagia
  category: Neurological
  frequency: FREQUENT
  description: Difficulty swallowing due to weakness of pharyngeal and esophageal muscles.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002015 | Dysphagia | Frequent (79-30%)"
    explanation: Orphanet lists dysphagia as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Bulbar dysfunction can manifest as dysphagia (trouble swallowing) and dysarthria (trouble speaking)."
    explanation: StatPearls article highlights dysphagia as a common bulbar manifestation in ALS.
  - reference: PMID:39207520
    reference_title: "Narrative review of diagnosis, management and treatment of dysphagia and sialorrhea in amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Throughout the disease, more than two-thirds of ALS patients experience dysphagia, regardless of the region of onset."
    explanation: Dysphagia-focused review reports that swallowing difficulty affects the majority of ALS patients.
- name: Drooling
  category: Neurological
  frequency: FREQUENT
  description: Excessive salivation due to impaired swallowing of saliva from bulbar motor neuron involvement.
  phenotype_term:
    preferred_term: Drooling
    term:
      id: HP:0002307
      label: Drooling
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002307 | Drooling | Frequent (79-30%)"
    explanation: Orphanet lists drooling as frequent in ALS.
  - reference: PMID:34920148
    reference_title: "Prevalence of Sialorrhea Among Amyotrophic Lateral Sclerosis Patients: A Systematic Review and Meta-Analysis."
    supports: SUPPORT
    snippet: "The pooled prevalence of sialorrhea among ALS patients was 30.8% (95% CI: 20.0%-44.2%)."
    explanation: Meta-analysis establishes pooled sialorrhea prevalence of 30.8% in ALS patients.
- name: Fatigable Weakness of Bulbar Muscles
  category: Neuromuscular
  frequency: FREQUENT
  description: Worsening of bulbar muscle function with repeated use, affecting speech and swallowing.
  phenotype_term:
    preferred_term: Fatigable weakness of bulbar muscles
    term:
      id: HP:0030192
      label: Fatigable weakness of bulbar muscles
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0030192 | Fatigable weakness of bulbar muscles | Frequent (79-30%)"
    explanation: Orphanet lists fatigable weakness of bulbar muscles as frequent in ALS.
- name: Fatigable Weakness of Swallowing Muscles
  category: Neuromuscular
  frequency: FREQUENT
  description: Worsening of swallowing function with repeated use due to progressive motor neuron loss.
  phenotype_term:
    preferred_term: Fatigable weakness of swallowing muscles
    term:
      id: HP:0030195
      label: Fatigable weakness of swallowing muscles
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0030195 | Fatigable weakness of swallowing muscles | Frequent (79-30%)"
    explanation: Orphanet lists fatigable weakness of swallowing muscles as frequent in ALS.
- name: Fatigable Weakness of Respiratory Muscles
  category: Respiratory
  frequency: FREQUENT
  description: Worsening respiratory muscle function with use, contributing to ventilatory failure.
  phenotype_term:
    preferred_term: Fatigable weakness of respiratory muscles
    term:
      id: HP:0030196
      label: Fatigable weakness of respiratory muscles
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0030196 | Fatigable weakness of respiratory muscles | Frequent (79-30%)"
    explanation: Orphanet lists fatigable weakness of respiratory muscles as frequent in ALS.
- name: Respiratory Insufficiency
  category: Respiratory
  frequency: FREQUENT
  description: Progressive weakness of diaphragm and intercostal muscles leading to ventilatory failure. This is the most common cause of death in ALS.
  phenotype_term:
    preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002878 | Respiratory failure | Frequent (79-30%)"
    explanation: Orphanet lists respiratory failure (HP:0002878) as frequent; this entry uses the more specific HP:0002747 (respiratory insufficiency due to muscle weakness) which captures the neuromuscular etiology.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Death usually occurs within 2 to 5 years from respiratory failure."
    explanation: Clinical overview states respiratory failure is the usual terminal event in ALS.
- name: Abnormality on Pulmonary Function Testing
  category: Respiratory
  frequency: FREQUENT
  description: Reduced forced vital capacity and other pulmonary function parameters due to respiratory muscle weakness.
  phenotype_term:
    preferred_term: Abnormality on pulmonary function testing
    term:
      id: HP:0030878
      label: Abnormality on pulmonary function testing
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0030878 | Abnormality on pulmonary function testing | Frequent (79-30%)"
    explanation: Orphanet lists abnormality on pulmonary function testing as frequent in ALS.
- name: Dyspnea
  category: Respiratory
  frequency: FREQUENT
  description: Breathlessness resulting from progressive respiratory muscle weakness.
  phenotype_term:
    preferred_term: Dyspnea
    term:
      id: HP:0002094
      label: Dyspnea
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002094 | Dyspnea | Frequent (79-30%)"
    explanation: Orphanet lists dyspnea as frequent in ALS.
- name: Orthopnea
  category: Respiratory
  frequency: OCCASIONAL
  description: Difficulty breathing while lying flat, indicating diaphragmatic weakness.
  phenotype_term:
    preferred_term: Orthopnea
    term:
      id: HP:0012764
      label: Orthopnea
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0012764 | Orthopnea | Occasional (29-5%)"
    explanation: Orphanet lists orthopnea as occasional in ALS.
- name: Skeletal Muscle Atrophy
  category: Neuromuscular
  frequency: FREQUENT
  description: Wasting of skeletal muscles due to denervation following motor neuron loss.
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003202 | Skeletal muscle atrophy | Frequent (79-30%)"
    explanation: Orphanet lists skeletal muscle atrophy as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Lower motor neuron signs include muscle atrophy, weakness, flaccid paralysis, absent reflexes, fasciculations, and fibrillations."
    explanation: Review details muscle atrophy as a key lower motor neuron sign in ALS.
- name: Distal Amyotrophy
  category: Neuromuscular
  frequency: FREQUENT
  description: Wasting of muscles in the hands and feet, often an early finding.
  phenotype_term:
    preferred_term: Distal amyotrophy
    term:
      id: HP:0003693
      label: Distal amyotrophy
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003693 | Distal amyotrophy | Frequent (79-30%)"
    explanation: Orphanet lists distal amyotrophy as frequent in ALS.
- name: Progressive Distal Muscular Atrophy
  category: Neuromuscular
  frequency: FREQUENT
  description: Progressive wasting of distal muscles over the course of disease.
  phenotype_term:
    preferred_term: Progressive distal muscular atrophy
    term:
      id: HP:0008955
      label: Progressive distal muscular atrophy
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0008955 | Progressive distal muscular atrophy | Frequent (79-30%)"
    explanation: Orphanet lists progressive distal muscular atrophy as frequent in ALS.
- name: Upper Limb Muscle Weakness
  category: Neuromuscular
  frequency: FREQUENT
  description: Weakness of arm and hand muscles, often presenting asymmetrically.
  phenotype_term:
    preferred_term: Upper limb muscle weakness
    term:
      id: HP:0003484
      label: Upper limb muscle weakness
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003484 | Upper limb muscle weakness | Frequent (79-30%)"
    explanation: Orphanet lists upper limb muscle weakness as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "the majority of the patients present with asymmetric limb weakness (80%) or bulbar dysfunction (20%)."
    explanation: StatPearls review confirms asymmetric limb weakness as the most common presentation.
- name: Lower Limb Muscle Weakness
  category: Neuromuscular
  frequency: FREQUENT
  description: Weakness of leg muscles leading to gait difficulties and falls.
  phenotype_term:
    preferred_term: Lower limb muscle weakness
    term:
      id: HP:0007340
      label: Lower limb muscle weakness
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0007340 | Lower limb muscle weakness | Frequent (79-30%)"
    explanation: Orphanet lists lower limb muscle weakness as frequent in ALS.
- name: Paralysis
  category: Neuromuscular
  frequency: FREQUENT
  description: Progressive loss of ability to move affected muscles due to motor neuron death.
  phenotype_term:
    preferred_term: Paralysis
    term:
      id: HP:0003470
      label: Paralysis
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003470 | Paralysis | Frequent (79-30%)"
    explanation: Orphanet lists paralysis as frequent in ALS.
- name: Muscle Spasm
  category: Neuromuscular
  frequency: FREQUENT
  description: Painful involuntary muscle contractions, a common and distressing symptom in ALS.
  phenotype_term:
    preferred_term: Muscle spasm
    term:
      id: HP:0003394
      label: Muscle spasm
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003394 | Muscle spasm | Frequent (79-30%)"
    explanation: Orphanet lists muscle spasm as frequent in ALS.
- name: Tongue Fasciculations
  category: Neurological
  frequency: OCCASIONAL
  diagnostic: true
  description: Involuntary twitching of the tongue, a characteristic finding of bulbar motor neuron involvement.
  phenotype_term:
    preferred_term: Tongue fasciculations
    term:
      id: HP:0001308
      label: Tongue fasciculations
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0001308 | Tongue fasciculations | Occasional (29-5%)"
    explanation: Orphanet lists tongue fasciculations as occasional in ALS.
- name: Tongue Atrophy
  category: Neurological
  frequency: FREQUENT
  description: Wasting of tongue muscles due to hypoglossal motor neuron loss.
  phenotype_term:
    preferred_term: Tongue atrophy
    term:
      id: HP:0012473
      label: Tongue atrophy
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0012473 | Tongue atrophy | Frequent (79-30%)"
    explanation: Orphanet lists tongue atrophy as frequent in ALS.
- name: Foot Dorsiflexor Weakness
  category: Neuromuscular
  frequency: OCCASIONAL
  description: Weakness of muscles that lift the foot, causing foot drop and gait impairment.
  phenotype_term:
    preferred_term: Foot dorsiflexor weakness
    term:
      id: HP:0009027
      label: Foot dorsiflexor weakness
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0009027 | Foot dorsiflexor weakness | Occasional (29-5%)"
    explanation: Orphanet lists foot dorsiflexor weakness as occasional in ALS.
- name: Steppage Gait
  category: Neuromuscular
  frequency: OCCASIONAL
  description: High-stepping gait pattern resulting from foot drop due to lower motor neuron involvement.
  phenotype_term:
    preferred_term: Steppage gait
    term:
      id: HP:0003376
      label: Steppage gait
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0003376 | Steppage gait | Occasional (29-5%)"
    explanation: Orphanet lists steppage gait as occasional in ALS.
- name: Weight Loss
  category: Constitutional
  frequency: FREQUENT
  description: Unintentional weight loss due to dysphagia, hypermetabolism, and muscle wasting. A negative prognostic factor.
  phenotype_term:
    preferred_term: Weight loss
    term:
      id: HP:0001824
      label: Weight loss
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0001824 | Weight loss | Frequent (79-30%)"
    explanation: Orphanet lists weight loss as frequent in ALS.
  - reference: PMID:23466470
    reference_title: "Nutrition management of amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Amyotrophic lateral sclerosis (ALS) is a progressive neurological disease with high risk of malnutrition."
    explanation: Nutrition review confirms ALS carries high risk of malnutrition and weight loss.
- name: Cachexia
  category: Constitutional
  frequency: OCCASIONAL
  description: Severe wasting and weight loss in advanced disease.
  phenotype_term:
    preferred_term: Cachexia
    term:
      id: HP:0004326
      label: Cachexia
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0004326 | Cachexia | Occasional (29-5%)"
    explanation: Orphanet lists cachexia as occasional in ALS.
- name: Fatigue
  category: Constitutional
  frequency: FREQUENT
  description: Pervasive tiredness and reduced energy common across the disease course.
  phenotype_term:
    preferred_term: Fatigue
    term:
      id: HP:0012378
      label: Fatigue
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0012378 | Fatigue | Frequent (79-30%)"
    explanation: Orphanet lists fatigue as frequent in ALS.
  - reference: PMID:23466470
    reference_title: "Nutrition management of amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Symptoms of dysphagia, depression, cognitive impairment, difficulty with self-feeding and meal preparation, hypermetabolism, anxiety, respiratory insufficiency, and fatigue with meals increase the risk of malnutrition."
    explanation: Nutrition review identifies fatigue as a contributing symptom to malnutrition risk in ALS.
- name: Pain
  category: Neurological
  frequency: FREQUENT
  description: Physical pain is common in ALS, often related to muscle cramps, spasticity, immobility, and joint complications.
  phenotype_term:
    preferred_term: Pain
    term:
      id: HP:0012531
      label: Pain
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0012531 | Pain | Frequent (79-30%)"
    explanation: Orphanet lists pain as frequent in ALS.
  - reference: PMID:33661072
    reference_title: "Prevalence of pain in amyotrophic lateral sclerosis: a systematic review and meta-analysis."
    supports: SUPPORT
    snippet: "Pooled prevalence of pain in ALS across all studies was 60% (95% CI = 50-69%), with a high degree of heterogeneity"
    explanation: Systematic review and meta-analysis establishes pain prevalence of 60% across ALS populations.
- name: Xerostomia
  category: Neurological
  frequency: FREQUENT
  description: Dry mouth, which may paradoxically coexist with drooling due to impaired swallowing.
  phenotype_term:
    preferred_term: Xerostomia
    term:
      id: HP:0000217
      label: Xerostomia
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0000217 | Xerostomia | Frequent (79-30%)"
    explanation: Orphanet lists xerostomia as frequent in ALS.
- name: Emotional Lability
  category: Neuropsychiatric
  frequency: FREQUENT
  description: Pseudobulbar affect characterized by involuntary, exaggerated, or inappropriate episodes of laughing or crying.
  phenotype_term:
    preferred_term: Emotional lability
    term:
      id: HP:0000712
      label: Emotional lability
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0000712 | Emotional lability | Frequent (79-30%)"
    explanation: Orphanet lists emotional lability as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Some patients may also present with Pseudobulbar affect, which is dysregulation of emotional responses exhibited by excessive laughter or crying."
    explanation: StatPearls review describes pseudobulbar affect as dysregulated emotional responses in ALS patients.
- name: Depression
  category: Neuropsychiatric
  frequency: FREQUENT
  description: Depressive symptoms are common in ALS and may reflect both psychological burden and neurobiological changes.
  phenotype_term:
    preferred_term: Depression
    term:
      id: HP:0000716
      label: Depression
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0000716 | Depression | Frequent (79-30%)"
    explanation: Orphanet lists depression as frequent in ALS.
  - reference: PMID:23466470
    reference_title: "Nutrition management of amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Symptoms of dysphagia, depression, cognitive impairment, difficulty with self-feeding and meal preparation, hypermetabolism, anxiety, respiratory insufficiency, and fatigue with meals increase the risk of malnutrition."
    explanation: Nutrition review identifies depression as a contributing symptom in ALS.
- name: Anxiety
  category: Neuropsychiatric
  frequency: FREQUENT
  description: Anxiety symptoms commonly co-occur with ALS.
  phenotype_term:
    preferred_term: Anxiety
    term:
      id: HP:0000739
      label: Anxiety
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0000739 | Anxiety | Frequent (79-30%)"
    explanation: Orphanet lists anxiety as frequent in ALS.
  - reference: PMID:23466470
    reference_title: "Nutrition management of amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Symptoms of dysphagia, depression, cognitive impairment, difficulty with self-feeding and meal preparation, hypermetabolism, anxiety, respiratory insufficiency, and fatigue with meals increase the risk of malnutrition."
    explanation: Nutrition review lists anxiety among symptoms contributing to malnutrition in ALS.
- name: Atypical Behavior
  category: Neuropsychiatric
  frequency: FREQUENT
  description: Behavioral changes including apathy, disinhibition, and loss of empathy, part of the ALS-FTD continuum.
  phenotype_term:
    preferred_term: Atypical behavior
    term:
      id: HP:0000708
      label: Atypical behavior
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0000708 | Atypical behavior | Frequent (79-30%)"
    explanation: Orphanet lists atypical behavior as frequent in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Patients can also display changes in behavior due to frontotemporal dysfunction, and about 15% of patients develop frontotemporal dementia."
    explanation: StatPearls review confirms behavioral changes from frontotemporal dysfunction in ALS patients.
- name: Cognitive Impairment
  category: Neuropsychiatric
  frequency: FREQUENT
  description: Cognitive deficits, particularly in executive function, occur in up to 50% of ALS patients, part of the ALS-FTD continuum.
  phenotype_term:
    preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0100543 | Cognitive impairment | Frequent (79-30%)"
    explanation: Orphanet lists cognitive impairment as frequent in ALS.
  - reference: PMID:22305801
    reference_title: "Cognitive and clinical characteristics of patients with amyotrophic lateral sclerosis carrying a C9orf72 repeat expansion: a population-based cohort study."
    supports: SUPPORT
    snippet: "Cognitive impairment occurs in up to 50% of cases, and one in seven patients develops frank frontotemporal dementia (FTD)."
    explanation: Population-based study reports cognitive impairment in up to 50% of ALS cases.
- name: Frontotemporal Dementia
  category: Neuropsychiatric
  frequency: OCCASIONAL
  description: Co-morbid frontotemporal dementia occurs in approximately 15% of ALS patients, representing the severe end of the ALS-FTD continuum.
  phenotype_term:
    preferred_term: Frontotemporal dementia
    term:
      id: HP:0002145
      label: Frontotemporal dementia
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002145 | Frontotemporal dementia | Occasional (29-5%)"
    explanation: Orphanet lists frontotemporal dementia as occasional in ALS.
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "about 15% of patients develop frontotemporal dementia."
    explanation: StatPearls review reports approximately 15% of ALS patients develop frontotemporal dementia.
  - reference: PMID:38802173
    reference_title: "Amyotrophic lateral sclerosis; clinical features, differential diagnosis and pathology."
    supports: SUPPORT
    snippet: "ALS forms a clinical continuum with frontotemporal dementia (FTD), in which there are progressive language deficits or behavioral changes."
    explanation: Review describes ALS-FTD clinical continuum with overlapping genetics and pathology.
- name: Language Impairment
  category: Neuropsychiatric
  frequency: OCCASIONAL
  description: Language deficits as part of the frontotemporal dysfunction spectrum in ALS.
  phenotype_term:
    preferred_term: Language impairment
    term:
      id: HP:0002463
      label: Language impairment
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002463 | Language impairment | Occasional (29-5%)"
    explanation: Orphanet lists language impairment as occasional in ALS.
  - reference: PMID:38802173
    reference_title: "Amyotrophic lateral sclerosis; clinical features, differential diagnosis and pathology."
    supports: SUPPORT
    snippet: "ALS forms a clinical continuum with frontotemporal dementia (FTD), in which there are progressive language deficits or behavioral changes."
    explanation: ALS clinical features review describes progressive language deficits within the ALS-FTD spectrum.
- name: Sleep Disturbance
  category: Neurological
  frequency: OCCASIONAL
  description: Sleep disturbances including nocturnal hypoventilation, sleep fragmentation, and excessive daytime sleepiness.
  phenotype_term:
    preferred_term: Sleep disturbance
    term:
      id: HP:0002360
      label: Sleep disturbance
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002360 | Sleep abnormality | Occasional (29-5%)"
    explanation: Orphanet lists sleep disturbance as occasional in ALS.
- name: Spastic Paraparesis
  category: Neurological
  frequency: OCCASIONAL
  description: Stiffness and weakness of both lower limbs due to upper motor neuron involvement.
  phenotype_term:
    preferred_term: Spastic paraparesis
    term:
      id: HP:0002313
      label: Spastic paraparesis
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0002313 | Spastic paraparesis | Occasional (29-5%)"
    explanation: Orphanet lists spastic paraparesis as occasional in ALS.
- name: Jaw Hyperreflexia
  category: Neurological
  frequency: OCCASIONAL
  diagnostic: true
  description: Exaggerated jaw jerk reflex indicating upper motor neuron involvement in the brainstem.
  phenotype_term:
    preferred_term: Jaw hyperreflexia
    term:
      id: HP:0033683
      label: Jaw hyperreflexia
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0033683 | Jaw hyperreflexia | Occasional (29-5%)"
    explanation: Orphanet lists jaw hyperreflexia as occasional in ALS.
- name: Laryngospasm
  category: Neurological
  frequency: VERY_RARE
  description: Sudden involuntary closure of the vocal cords, causing brief episodes of breathing difficulty.
  phenotype_term:
    preferred_term: Laryngospasm
    term:
      id: HP:0025425
      label: Laryngospasm
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "HP:0025425 | Laryngospasm | Very rare (<4-1%)"
    explanation: Orphanet lists laryngospasm as very rare in ALS.
biochemical:
- name: Neurofilament Light Chain (NfL)
  presence: Elevated
  context: CSF and serum biomarker of axonal injury, elevated in ALS with prognostic value
  notes: Used for diagnosis, prognosis, and monitoring therapeutic response in clinical trials
  evidence:
  - reference: PMID:36543887
    reference_title: "Amyotrophic lateral sclerosis: a neurodegenerative disorder poised for successful therapeutic translation."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Plasma and cerebrospinal fluid (CSF) neurofilament protein levels look particularly promising and may improve the efficiency of future clinical trials and allow identification of responder subgroups."
    explanation: >-
      Translational review identifies plasma and CSF neurofilament as the most
      promising ALS biomarkers for trial enrichment and responder identification.
  - reference: PMID:36129998
    reference_title: "Trial of Antisense Oligonucleotide Tofersen for SOD1 ALS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tofersen led to greater reductions in concentrations of SOD1 in CSF and of neurofilament light chains in plasma than placebo."
    explanation: >-
      The VALOR phase 3 trial shows plasma neurofilament light chain falls with
      SOD1-lowering therapy, validating NfL as a pharmacodynamic biomarker of
      axonal injury that tracks treatment response in ALS.
- name: Phosphorylated Neurofilament Heavy Chain (pNfH)
  presence: Elevated
  context: CSF and serum biomarker of axonal injury
genetic:
- name: C9orf72 Repeat Expansion
  association: Causative
  notes: Most common genetic cause of ALS (40% familial, 5-10% sporadic); GGGGCC hexanucleotide repeat expansion
  inheritance:
  - name: Autosomal Dominant
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "C9ORF72 | C9orf72-SMCR8 complex subunit | hgnc:28337 | Disease-causing germline mutation(s) in"
    explanation: Orphanet lists C9ORF72 as harboring disease-causing germline mutations in ALS.
  - reference: PMID:21944778
    reference_title: "Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS."
    supports: SUPPORT
    snippet: "Analysis of extended clinical series found the C9ORF72 repeat expansion to be the most common genetic abnormality in both familial FTD (11.7%) and familial ALS (23.5%)"
    explanation: Original discovery paper establishing C9orf72 as the most common genetic cause of familial ALS.
  - reference: PMID:22406228
    reference_title: "Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This genetic lesion accounted for a large proportion (∼40·0%) of familial cases of ALS and FTD."
    explanation: Cross-sectional study's headline conclusion supports the ~40% familial figure cited in this entry's notes.
  - reference: PMID:22406228
    reference_title: "Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In patients with sporadic ALS, we identified the repeat expansion in 236 (7·0%) of 3377 white individuals from the USA, Europe, and Australia"
    explanation: Same study supports the 5-10% sporadic-ALS frequency cited in this entry's notes (7.0% in the largest white cohort).
- name: SOD1 Mutations
  association: Causative
  notes: First identified ALS gene; accounts for approximately 20% of familial ALS and 2% of sporadic cases
  inheritance:
  - name: Autosomal Dominant
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "SOD1 | superoxide dismutase 1 | hgnc:11179 | Disease-causing germline mutation(s) in"
    explanation: Orphanet lists SOD1 as harboring disease-causing germline mutations in ALS.
  - reference: PMID:8446170
    reference_title: "Mutations in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "We identified 11 different SOD1 missense mutations in 13 different FALS families."
    explanation: Original discovery paper identifying SOD1 mutations as a cause of familial ALS.
- name: TARDBP Mutations
  association: Causative
  notes: Encodes TDP-43 protein; mutations cause approximately 5% of familial ALS
  inheritance:
  - name: Autosomal Dominant
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "TARDBP | TAR DNA binding protein | hgnc:11571 | Disease-causing germline mutation(s) in"
    explanation: Orphanet lists TARDBP as harboring disease-causing germline mutations in ALS.
  - reference: PMID:35805149
    reference_title: "Gene Therapy in Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    snippet: "Mutations in C9orf72, SOD1, TAR DNA binding protein 43 (TARDBP), and fused in sarcoma (FUS) genes are the four most common ones."
    explanation: Gene therapy review highlights TARDBP among the most common ALS genes targeted by therapeutic strategies.
- name: FUS Mutations
  association: Causative
  notes: RNA-binding protein; mutations cause approximately 5% of familial ALS
  inheritance:
  - name: Autosomal Dominant
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "FUS | FUS RNA binding protein | hgnc:4010 | Disease-causing germline mutation(s) in"
    explanation: Orphanet lists FUS as harboring disease-causing germline mutations in ALS.
  - reference: PMID:35805149
    reference_title: "Gene Therapy in Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    snippet: "Mutations in C9orf72, SOD1, TAR DNA binding protein 43 (TARDBP), and fused in sarcoma (FUS) genes are the four most common ones."
    explanation: Review notes FUS among the four most common ALS genes and discusses gene-targeted therapies.
- name: NEK1 Variants
  association: Susceptibility
  notes: Risk variants found in nearly 3% of ALS cases
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "NEK1 | NIMA related kinase 1 | hgnc:7744 | Major susceptibility factor in"
    explanation: Orphanet lists NEK1 as a major susceptibility factor in ALS.
  - reference: PMID:27455347
    reference_title: "NEK1 variants confer susceptibility to amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "In total, we observed NEK1 risk variants in nearly 3% of ALS cases. NEK1 has been linked to several cellular functions, including cilia formation, DNA-damage response, microtubule stability, neuronal morphology and axonal polarity."
    explanation: Large-scale genetic study identifying NEK1 variants as risk factors for ALS.
- name: ATXN2 Intermediate-Length Repeat Expansion
  gene_term:
    preferred_term: ATXN2
    term:
      id: hgnc:10555
      label: ATXN2
  association: Susceptibility
  notes: >-
    Intermediate-length polyglutamine (polyQ) expansions of 27-33 repeats in ATXN2 are a
    relatively common ALS susceptibility factor. ATXN2 is a potent modifier of TDP-43
    toxicity, linking this risk allele to the core TDP-43 proteinopathy axis; ATXN2
    lowering (e.g., antisense oligonucleotides) is under therapeutic investigation.
  evidence:
  - reference: PMID:20740007
    reference_title: "Ataxin-2 intermediate-length polyglutamine expansions are associated with increased risk for ALS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found that intermediate-length polyQ expansions (27-33 glutamines) in ATXN2 were significantly associated with ALS. These data establish ATXN2 as a relatively common ALS susceptibility gene."
    explanation: >-
      Landmark study analyzing the ATXN2 polyQ repeat in 915 ALS patients establishes
      intermediate-length expansions as a common ALS susceptibility factor and identifies
      ATXN2 as a modifier of TDP-43 toxicity.
- name: ARHGEF28
  gene_term:
    preferred_term: ARHGEF28
    term:
      id: hgnc:30322
      label: ARHGEF28
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_ac27cecc-9749-4c69-88fa-fe83b2d49568-2024-03-28T190000.000Z
    reference_title: "ARHGEF28 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ARHGEF28 | HGNC:30322 | amyotrophic lateral sclerosis | MONDO:0004976 | SD | Limited"
    explanation: ClinGen classifies the ARHGEF28-amyotrophic lateral sclerosis gene-disease relationship as limited with semidominant inheritance.
- name: ARPP21
  gene_term:
    preferred_term: ARPP21
    term:
      id: hgnc:16968
      label: ARPP21
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_02d4089a-94dd-42b6-ab09-dc258db00ae9-2025-01-14T200000.000Z
    reference_title: "ARPP21 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ARPP21 | HGNC:16968 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the ARPP21-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: CAV1
  gene_term:
    preferred_term: CAV1
    term:
      id: hgnc:1527
      label: CAV1
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_cab41529-d295-466c-8821-75a16bb12c38-2023-12-21T170000.000Z
    reference_title: "CAV1 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CAV1 | HGNC:1527 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the CAV1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: CAV2
  gene_term:
    preferred_term: CAV2
    term:
      id: hgnc:1528
      label: CAV2
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_38faae4c-13ae-4c28-bea4-43e3ad15e178-2023-12-21T170000.000Z
    reference_title: "CAV2 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CAV2 | HGNC:1528 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the CAV2-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: CFAP410
  gene_term:
    preferred_term: CFAP410
    term:
      id: hgnc:1260
      label: CFAP410
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_bde7edf1-ccfa-443e-a917-cf3d2dd9cba6-2023-12-12T180000.000Z
    reference_title: "CFAP410 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CFAP410 | HGNC:1260 | amyotrophic lateral sclerosis | MONDO:0004976 | SD | Limited"
    explanation: ClinGen classifies the CFAP410-amyotrophic lateral sclerosis gene-disease relationship as limited with semidominant inheritance.
- name: DCTN1
  gene_term:
    preferred_term: DCTN1
    term:
      id: hgnc:2711
      label: DCTN1
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_5cd19f2c-2499-417f-94c8-2bd4bedf34ef-2023-08-04T160000.000Z
    reference_title: "DCTN1 / amyotrophic lateral sclerosis (Moderate)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "DCTN1 | HGNC:2711 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Moderate"
    explanation: ClinGen classifies the DCTN1-amyotrophic lateral sclerosis gene-disease relationship as moderate with autosomal dominant inheritance.
- name: DNAJC7
  gene_term:
    preferred_term: DNAJC7
    term:
      id: hgnc:12392
      label: DNAJC7
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_e2a12a19-b37a-4654-87fa-3a921c202c87-2022-10-27T160000.000Z
    reference_title: "DNAJC7 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "DNAJC7 | HGNC:12392 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the DNAJC7-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: GLE1
  gene_term:
    preferred_term: GLE1
    term:
      id: hgnc:4315
      label: GLE1
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_0284b3cd-38af-4309-8ce4-054a0379e693-2023-10-10T160000.000Z
    reference_title: "GLE1 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "GLE1 | HGNC:4315 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the GLE1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: GLT8D1
  gene_term:
    preferred_term: GLT8D1
    term:
      id: hgnc:24870
      label: GLT8D1
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_a2c4f919-ccb5-4d9f-a604-5ed19e19057e-2025-01-14T200000.000Z
    reference_title: "GLT8D1 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "GLT8D1 | HGNC:24870 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the GLT8D1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: LGALSL
  gene_term:
    preferred_term: LGALSL
    term:
      id: hgnc:25012
      label: LGALSL
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_5a2db59f-5293-4e5d-ae34-5a38d8c6ebdf-2023-02-14T170000.000Z
    reference_title: "LGALSL / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "LGALSL | HGNC:25012 | amyotrophic lateral sclerosis | MONDO:0004976 | UD | Limited"
    explanation: ClinGen classifies the LGALSL-amyotrophic lateral sclerosis gene-disease relationship as limited with undetermined inheritance.
- name: NEFH
  gene_term:
    preferred_term: NEFH
    term:
      id: hgnc:7737
      label: NEFH
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_6c71deac-6b11-4947-8834-8391d516a9c9-2023-03-23T160000.000Z
    reference_title: "NEFH / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "NEFH | HGNC:7737 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the NEFH-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: NUP50
  gene_term:
    preferred_term: NUP50
    term:
      id: hgnc:8065
      label: NUP50
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_0ce3418e-c7e5-452b-9db6-661571331822-2024-06-27T160000.000Z
    reference_title: "NUP50 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "NUP50 | HGNC:8065 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the NUP50-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: PRPH
  gene_term:
    preferred_term: PRPH
    term:
      id: hgnc:9461
      label: PRPH
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_3d11b04d-508a-4f91-9d9a-b5016fd0b940-2022-12-13T170000.000Z
    reference_title: "PRPH / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "PRPH | HGNC:9461 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the PRPH-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: SPTLC2
  gene_term:
    preferred_term: SPTLC2
    term:
      id: hgnc:11278
      label: SPTLC2
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_402cf65d-02f1-4cc1-a45e-b3bd3ad48b86-2024-06-26T160000.000Z
    reference_title: "SPTLC2 / amyotrophic lateral sclerosis (Strong)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SPTLC2 | HGNC:11278 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Strong"
    explanation: ClinGen classifies the SPTLC2-amyotrophic lateral sclerosis gene-disease relationship as strong with autosomal dominant inheritance.
- name: SS18L1
  gene_term:
    preferred_term: SS18L1
    term:
      id: hgnc:15592
      label: SS18L1
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_6e148a06-50fc-45f3-90ea-023dc8687577-2023-05-25T160000.000Z
    reference_title: "SS18L1 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SS18L1 | HGNC:15592 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the SS18L1-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
- name: TAF15
  gene_term:
    preferred_term: TAF15
    term:
      id: hgnc:11547
      label: TAF15
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_605446ae-fd1f-4451-bd49-643c24cd652e-2021-11-03T020945.214Z
    reference_title: "TAF15 / amyotrophic lateral sclerosis (Limited)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "TAF15 | HGNC:11547 | amyotrophic lateral sclerosis | MONDO:0004976 | AD | Limited"
    explanation: ClinGen classifies the TAF15-amyotrophic lateral sclerosis gene-disease relationship as limited with autosomal dominant inheritance.
environmental:
- name: Heavy Metal Exposure
  notes: Occupational and environmental exposure to lead, cadmium, mercury, and other heavy metals has been associated with increased ALS risk. Prospective pre-diagnostic blood-metal data (which minimize reverse causation) implicate cadmium and lead, with zinc inversely associated.
  evidence:
  - reference: PMID:31578652
    reference_title: "Population-based study of environmental/occupational lead exposure and amyotrophic lateral sclerosis: a systematic review and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The ratio of maximal/minimal lead exposure yielded a pooled odds ratio (OR) of 1.46 (95% confidence interval (CI) 1.16-1.83) with moderate heterogeneity (I2 = 51.8%; p = 0.019)."
    explanation: Meta-analysis finds lead exposure positively associated with ALS risk across population-based studies.
  - reference: PMID:33068316
    reference_title: "Blood Metal Levels and Amyotrophic Lateral Sclerosis Risk: A Prospective Cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "cadmium and lead may be associated with an increased risk of ALS and zinc with a decreased risk. This is the first study to evaluate predisease metal levels in blood, thus minimizing reverse causation."
    explanation: Nested case-control study in the prospective EPIC cohort measured pre-diagnostic blood metals, implicating cadmium and lead (and protective zinc) with a design that minimizes reverse causation. Identified as an un-integrated finding from the ALS environmental-toxicity deep-research report.
- name: Pesticide Exposure
  notes: Agricultural pesticide exposure has been linked to increased ALS incidence in epidemiological studies.
  evidence:
  - reference: PMID:22521219
    reference_title: "Pesticide exposure and amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "In the meta-analysis, ALS was associated with use of pesticides as a group (1.9, 1.1-3.1)."
    explanation: Systematic review and AHS cohort analysis report elevated ALS odds with pesticide exposure.
- name: Military Service
  notes: Veterans have approximately twice the risk of developing ALS compared to the general population, possibly related to environmental exposures.
  evidence:
  - reference: PMID:14504315
    reference_title: "Occurrence of amyotrophic lateral sclerosis among Gulf War veterans."
    supports: SUPPORT
    snippet: "A significant elevated risk of ALS occurred among all deployed personnel (RR = 1.92; 95% CL = 1.29, 2.84)"
    explanation: Gulf War veteran cohort showed nearly twofold higher ALS risk compared with non-deployed personnel.
- name: Smoking
  notes: >-
    Cigarette smoking is the most consistently reported environmental ALS risk factor,
    though the overall association is modest; in this meta-analysis the clearest signal
    is a sex-specific increased risk in women (ever-smoker RR 1.66, 95% CI 1.31-2.10),
    while the overall pooled estimates were not statistically significant.
  evidence:
  - reference: PMID:20639382
    reference_title: "Smoking and the risk of amyotrophic lateral sclerosis: a systematic review and meta-analysis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "The pooled RR (95% CI) of ALS was 1.28 (0.97 to 1.68) for current versus never smokers and 1.12 (0.98 to 1.27) for ever versus never smokers."
    explanation: Meta-analysis of case-control and cohort studies found overall pooled relative risks that were elevated but not statistically significant (confidence intervals crossing 1.0), providing only partial support for smoking as an ALS risk factor.
  - reference: PMID:20639382
    reference_title: "Smoking and the risk of amyotrophic lateral sclerosis: a systematic review and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "was 0.86 (0.71 to 1.03) in men and 1.66 (1.31 to 2.10) in women."
    explanation: Sex-stratified analysis shows a statistically significant elevated ALS risk in women who ever smoked (RR 1.66, 95% CI 1.31-2.10) but not in men, supporting the sex-specific smoking-ALS association.
- name: Repetitive Head Trauma and Contact Sports
  notes: Repetitive concussive head and cervical-spinal trauma, particularly from professional contact sports (American football, soccer/association football, boxing), is associated with a markedly increased risk of ALS; head trauma is also an independent risk factor in broad risk-factor meta-analyses. The association overlaps the trauma-driven TDP-43 proteinopathy seen in chronic traumatic encephalopathy.
  evidence:
  - reference: PMID:30775214
    reference_title: "Contact Sports as a Risk Factor for Amyotrophic Lateral Sclerosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "repetitive concussive head and cervical spinal trauma result in an increased risk of ALS compared with the general population or nonsport controls."
    explanation: Systematic review concludes that contact sports involving repetitive concussive head and cervical-spinal trauma increase ALS risk (with a pooled rate ratio of 8.52 for professional such sports). Identified as an un-integrated finding from the ALS environmental-toxicity deep-research report.
  - reference: PMID:37284659
    reference_title: "Risk factors associated with amyotrophic lateral sclerosis based on the observational study: a systematic review and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "head trauma (OR = 1.26, 95% CI = 1.13, 1.40)"
    explanation: Comprehensive observational meta-analysis identifies head trauma as an independent risk factor for ALS, corroborating the contact-sports signal.
treatments:
- name: Riluzole
  description: >
    Glutamate antagonist that modestly extends survival by 2-3 months. It is the first
    FDA-approved treatment for ALS and works by reducing excitotoxic neuronal damage.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: riluzole
      term:
        id: NCIT:C47704
        label: Riluzole
  evidence:
  - reference: PMID:8302340
    reference_title: "A controlled trial of riluzole in amyotrophic lateral sclerosis. ALS/Riluzole Study Group."
    supports: SUPPORT
    snippet: "The antiglutamate agent riluzole appears to slow the progression of amyotrophic lateral sclerosis, and it may improve survival in patients with disease of bulbar onset."
    explanation: Landmark trial demonstrating riluzole's survival benefit in ALS patients.
  target_mechanisms:
  - target: Glutamate Excitotoxicity
    treatment_effect: INHIBITS
    description: >-
      Riluzole blocks voltage-gated sodium channels and reduces glutamate release
      at presynaptic terminals, attenuating excitotoxic motor neuron injury.
- name: Edaravone
  description: >
    Antioxidant that may slow functional decline in a subset of ALS patients. It reduces
    oxidative stress and has shown benefit in early-stage patients.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: edaravone
      term:
        id: CHEBI:31530
        label: edaravone
  evidence:
  - reference: PMID:28522181
    reference_title: "Safety and efficacy of edaravone in well defined patients with amyotrophic lateral sclerosis: a randomised, double-blind, placebo-controlled trial."
    supports: SUPPORT
    snippet: "Edaravone showed efficacy in a small subset of people with ALS who met criteria identified in post-hoc analysis of a previous phase 3 study, showing a significantly smaller decline of ALSFRS-R score compared with placebo."
    explanation: Phase 3 trial demonstrating edaravone slows functional decline in early-stage ALS patients.
  - reference: PMID:35006266
    reference_title: "Safety and Effectiveness of Long-term Intravenous Administration of Edaravone for Treatment of Patients With Amyotrophic Lateral Sclerosis."
    supports: REFUTE
    snippet: "although long-term intravenous edaravone therapy for patients with ALS was feasible and mainly well tolerated, it was not associated with any disease-modifying benefit."
    explanation: Real-world cohort study found long-term intravenous edaravone well tolerated but without additional disease-modifying benefit versus standard therapy.
  target_mechanisms:
  - target: Oxidative Stress
    treatment_effect: INHIBITS
    description: >-
      Edaravone is a free-radical scavenger that neutralizes reactive oxygen
      species, reducing oxidative neuronal injury in motor neurons.
- name: Tofersen
  therapeutic_modality: ANTISENSE_OLIGONUCLEOTIDE
  aso_details:
    aso_mechanism: RNASE_H_KNOCKDOWN
    target_gene:
      preferred_term: SOD1
      term:
        id: hgnc:11179
        label: SOD1
    target_transcript: SOD1 mRNA
    aso_chemistry: TWO_PRIME_O_METHOXYETHYL
    conjugation: UNCONJUGATED
  description: >
    Antisense oligonucleotide therapy approved for SOD1-ALS that reduces SOD1 protein
    production, targeting the underlying genetic cause in this subset of patients.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: tofersen
      term:
        id: NCIT:C166584
        label: Tofersen
  evidence:
  - reference: PMID:32640130
    reference_title: "Phase 1-2 Trial of Antisense Oligonucleotide Tofersen for SOD1 ALS."
    supports: SUPPORT
    snippet: "In adults with ALS due to SOD1 mutations, CSF SOD1 concentrations decreased at the highest concentration of tofersen administered intrathecally over a period of 12 weeks."
    explanation: Phase 1-2 trial demonstrating tofersen reduces CSF SOD1 levels in SOD1-ALS patients.
  - reference: PMID:36129998
    reference_title: "Trial of Antisense Oligonucleotide Tofersen for SOD1 ALS."
    supports: SUPPORT
    snippet: "The intrathecally administered antisense oligonucleotide tofersen reduces synthesis of the superoxide dismutase 1 (SOD1) protein and is being studied in patients with amyotrophic lateral sclerosis (ALS) associated with mutations in SOD1 (SOD1 ALS)."
    explanation: VALOR pivotal phase 3 trial (the basis for tofersen's FDA approval) confirms the antisense mechanism reduces SOD1 protein synthesis in SOD1 ALS.
  - reference: PMID:36543887
    reference_title: "Amyotrophic lateral sclerosis: a neurodegenerative disorder poised for successful therapeutic translation."
    supports: SUPPORT
    snippet: "Significant discoveries and advances have been made in ALS preclinical models, genetics, pathology, biomarkers, imaging and clinical readouts over the last 10-15 years."
    explanation: Translational review highlights recent advances enabling gene-targeted therapies like tofersen.
  target_mechanisms:
  - target: Motor Neuron Degeneration
    treatment_effect: MODULATES
    description: >-
      Tofersen reduces mutant SOD1 protein levels via RNase H-mediated mRNA
      knockdown, reducing the SOD1-driven oxidative and proteotoxic burden that
      accelerates motor neuron loss in SOD1-ALS.
- name: Jacifusen (ION363)
  therapeutic_modality: ANTISENSE_OLIGONUCLEOTIDE
  aso_details:
    aso_mechanism: RNASE_H_KNOCKDOWN
    target_gene:
      preferred_term: FUS
      term:
        id: hgnc:4010
        label: FUS
    target_transcript: FUS pre-mRNA
  description: >
    Investigational antisense oligonucleotide (ION363, also known as ulefnersen) that
    non-allele-specifically silences FUS to lower wild-type and mutant FUS protein,
    targeting the gain-of-function genetic cause in FUS-ALS. Delivered by serial
    intrathecal injection; evaluated in an expanded-access case series and an ongoing
    clinical trial.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ulefnersen
      term:
        id: NCIT:C188629
        label: Ulefnersen
  evidence:
  - reference: PMID:40414239
    reference_title: "Antisense oligonucleotide jacifusen for FUS-ALS: an investigator-initiated, multicentre, open-label case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Jacifusen is an antisense oligonucleotide targeting FUS pre-mRNA, previously shown to delay neurodegeneration in a mouse model and potentially slow functional decline in a first-in-human study."
    explanation: Lancet expanded-access case series confirms jacifusen is an ASO targeting FUS pre-mRNA, supporting the FUS-knockdown mechanism of this treatment.
  - reference: PMID:40414239
    reference_title: "Antisense oligonucleotide jacifusen for FUS-ALS: an investigator-initiated, multicentre, open-label case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Biochemical and immunohistochemical analysis of CNS tissue samples from four participants showed reduced FUS protein levels and an apparent decrease in the burden of FUS pathology."
    explanation: Post-mortem CNS analysis in treated patients demonstrates jacifusen lowers FUS protein and FUS-aggregate burden, the intended target-engagement readout in humans.
  - reference: PMID:35075293
    reference_title: "Antisense oligonucleotide silencing of FUS expression as a therapeutic approach in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "ION363, a non-allele-specific FUS antisense oligonucleotide, efficiently silences Fus and reduces postnatal levels of FUS protein in the brain and spinal cord, delaying motor neuron degeneration."
    explanation: Preclinical FUS knock-in mouse study establishes that ION363 silences Fus and delays motor neuron degeneration, the model-organism basis for the human program.
  target_mechanisms:
  - target: Motor Neuron Degeneration
    treatment_effect: MODULATES
    description: >-
      Jacifusen silences FUS expression via RNase H-mediated knockdown, reducing
      mutant FUS protein aggregation and toxicity in motor neurons and delaying
      neurodegeneration in FUS-ALS.
- name: Triumeq
  description: >
    Antiretroviral therapy (combination of dolutegravir, lamivudine, and abacavir) proposed for treating TDP-43-associated ALS
    through modulation of endogenous retroviruses. In preclinical models, Triumeq transiently and modestly improves early motor
    function without impacting overall disease progression, and reduces TDP-43-driven neuroinflammation via suppression of
    transcription factor ATF4 and inflammatory markers CXCL10 and IRF-1.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: abacavir/dolutegravir/lamivudine
      term:
        id: NCIT:C157543
        label: Abacavir/Dolutegravir/Lamivudine
  target_mechanisms:
  - target: Endogenous Retrovirus Reactivation and TDP-43 Feedback
    treatment_effect: INHIBITS
    description: >-
      Triumeq's antiretroviral components (the integrase inhibitor dolutegravir
      plus the reverse-transcriptase inhibitors abacavir and lamivudine) target
      the ERV (HERV-K) reactivation arm of the ERV-TDP-43 feedback loop.
  - target: Neuroinflammation
    treatment_effect: INHIBITS
    description: >
      Triumeq suppresses TDP-43-driven inflammatory gene expression in the ALS
      neuroinflammation axis, including ATF4, CXCL10, and IRF-1.
    evidence:
    - reference: PMID:42204279
      reference_title: "Evaluation of triumeq treatment on a TDP-43 mouse model of amyotrophic Lateral sclerosis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In this TDP-43 ALS mouse model, there was a positive association of TDP-43 mRNA levels with transcription factor ATF4, and inflammatory markers CXCL10 and IRF-1, and Triumeq treatment negated this association."
      explanation: Triumeq negated TDP-43-associated inflammatory marker upregulation, linking the treatment to inhibition of the Neuroinflammation pathophysiology node.
  evidence:
  - reference: PMID:42204279
    reference_title: "Evaluation of triumeq treatment on a TDP-43 mouse model of amyotrophic Lateral sclerosis."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Triumeq treatment significantly improved motor function early on in the disease course"
    explanation: Preclinical study shows early motor function improvement in the TDP-43 ALS mouse model, but the abstract qualifies the effect as transient and modest with no impact on other progression markers or disease endpoint.
  - reference: PMID:42204279
    reference_title: "Evaluation of triumeq treatment on a TDP-43 mouse model of amyotrophic Lateral sclerosis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In this TDP-43 ALS mouse model, there was a positive association of TDP-43 mRNA levels with transcription factor ATF4, and inflammatory markers CXCL10 and IRF-1, and Triumeq treatment negated this association."
    explanation: Triumeq modulates TDP-43-driven neuroinflammation by suppressing ATF4 and inflammatory cytokines in disease model.
- name: Sodium Phenylbutyrate-Taurursodiol (AMX0035)
  description: >
    Fixed-dose combination of sodium phenylbutyrate and taurursodiol (tauroursodeoxycholic
    acid) intended to reduce endoplasmic-reticulum and mitochondrial stress-mediated motor
    neuron death, marketed as Relyvrio (US) / Albrioza (Canada). The phase 2 CENTAUR trial
    showed slower functional decline, supporting accelerated FDA approval in 2022, but the
    confirmatory phase 3 PHOENIX trial showed no benefit at 48 weeks and the sponsor
    voluntarily withdrew the drug from the market in 2024. Included here to document a
    withdrawn ALS therapy whose disease-modifying benefit was not confirmed.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sodium phenylbutyrate
      term:
        id: CHEBI:75316
        label: sodium phenylbutyrate
    - preferred_term: tauroursodeoxycholic acid
      term:
        id: CHEBI:80774
        label: tauroursodeoxycholic acid
  evidence:
  - reference: PMID:32877582
    reference_title: "Trial of Sodium Phenylbutyrate-Taurursodiol for Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the mean rate of change in the ALSFRS-R score was -1.24 points per month with the active drug and -1.66 points per month with placebo (difference, 0.42 points per month; 95% confidence interval, 0.03 to 0.81; P = 0.03)."
    explanation: >-
      The phase 2 CENTAUR randomized controlled trial showed a statistically significant
      slowing of ALSFRS-R functional decline versus placebo — the result that supported the
      2022 accelerated FDA approval.
  - reference: PMID:38909349
    reference_title: "Sodium Phenylbutyrate and Tauroursodeoxycholic Acid: A Story of Hope Turned to Disappointment in Amyotrophic Lateral Sclerosis Treatment."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "results from the Phase 3 PHOENIX trial (NCT05021536) showed no change in ALSFRS-R total score at 48 weeks."
    explanation: >-
      The confirmatory phase 3 PHOENIX trial found no effect on the primary functional
      endpoint, refuting a disease-modifying benefit and reversing the CENTAUR signal.
  - reference: PMID:38909349
    reference_title: "Sodium Phenylbutyrate and Tauroursodeoxycholic Acid: A Story of Hope Turned to Disappointment in Amyotrophic Lateral Sclerosis Treatment."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "the sponsor company initiated the process with the US FDA and Health Canada to voluntarily withdraw the marketing authorizations for PB-TUDCA."
    explanation: >-
      Following the negative PHOENIX trial, the sponsor voluntarily withdrew marketing
      authorizations in the US and Canada (2024), documenting the therapy's removal from clinical use.
- name: Non-invasive Ventilation
  description: >
    Respiratory support using BiPAP or similar devices to assist breathing as respiratory
    muscles weaken. This improves quality of life and extends survival.
  treatment_term:
    preferred_term: noninvasive ventilation
    term:
      id: NCIT:C171457
      label: Non-Invasive Mechanical Ventilation
  evidence:
  - reference: PMID:16426990
    reference_title: "Effects of non-invasive ventilation on survival and quality of life in patients with amyotrophic lateral sclerosis: a randomised controlled trial."
    supports: SUPPORT
    snippet: "This subgroup showed improvement in several measures of quality of life and a median survival benefit of 205 days (p=0.006) with maintained quality of life for most of this period."
    explanation: Randomized controlled trial demonstrated non-invasive ventilation improves quality of life and extends survival in ALS patients with preserved bulbar function.
  - reference: PMID:39019674
    reference_title: "Proposals from a French expert panel for respiratory care in ALS patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Non-invasive ventilation (NIV), which is the main recognized treatment for alleviating the symptoms of respiratory failure, prolongs survival and improves quality of life."
    explanation: The French expert-panel respiratory-care guideline affirms non-invasive ventilation as the main recognized treatment for ALS respiratory failure, prolonging survival and improving quality of life.
- name: Physical Therapy
  description: >
    Range of motion exercises and adaptive strategies to maintain function and prevent
    complications such as contractures.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  evidence:
  - reference: PMID:24510737
    reference_title: "Rehabilitation in amyotrophic lateral sclerosis: why it matters."
    supports: SUPPORT
    snippet: "Multidisciplinary care includes rehabilitation interventions that have the goal of assisting people to teach their fullest potential despite the presence of a disabling disease."
    explanation: Review describes how rehabilitation including physical therapy helps maximize independence and function in ALS patients.
- name: Speech Therapy
  description: >
    Techniques to optimize communication and swallowing safety, including augmentative
    and alternative communication devices.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  evidence:
  - reference: PMID:24510737
    reference_title: "Rehabilitation in amyotrophic lateral sclerosis: why it matters."
    supports: SUPPORT
    snippet: "This review will present rehabilitation strategies that can be utilized to maximize patient independence, function, safety, and quality of life, and to minimize disease-related symptoms."
    explanation: Review covers multidisciplinary rehabilitation including speech therapy for ALS patients.
- name: Percutaneous Endoscopic Gastrostomy
  description: >
    Feeding tube placement to maintain nutrition when swallowing becomes unsafe or
    inadequate due to bulbar involvement.
  treatment_term:
    preferred_term: Percutaneous Endoscopic Gastrostomy
    term:
      id: NCIT:C106040
      label: Percutaneous Endoscopic Gastrostomy
  evidence:
  - reference: PMID:39207520
    reference_title: "Narrative review of diagnosis, management and treatment of dysphagia and sialorrhea in amyotrophic lateral sclerosis."
    supports: SUPPORT
    snippet: "Early discussion of potential treatments such as high-calorie diets or percutaneous endoscopic gastrostomy (PEG) is crucial."
    explanation: Dysphagia management review underscores PEG as an essential intervention when nutrition is compromised in ALS.
- name: Multidisciplinary Care
  description: >
    Coordinated care from neurologists, pulmonologists, physical therapists, occupational
    therapists, speech therapists, nutritionists, and palliative care specialists extends
    survival and improves quality of life.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:24510737
    reference_title: "Rehabilitation in amyotrophic lateral sclerosis: why it matters."
    supports: SUPPORT
    snippet: "Multidisciplinary care includes rehabilitation interventions that have the goal of assisting people to teach their fullest potential despite the presence of a disabling disease."
    explanation: Rehabilitation review emphasizes multidisciplinary care as core to ALS management to optimize function and quality of life.
prevalence:
- population: Europe
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_low: 1.0
  rate_high: 9.0
  notes: Orphanet European point-prevalence class 1-9 / 100,000 (band-only source; no point estimate reported).
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "1-9 / 100 000 | Europe | Point prevalence | PMID:19192301,EXPERT"
    explanation: Orphanet epidemiology table reports a European point prevalence of 1-9 per 100,000.
- population: Europe
  measure_type: ANNUAL_INCIDENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_low: 1.0
  rate_high: 9.0
  notes: Orphanet European annual-incidence class 1-9 / 100,000 (band-only source; no point estimate reported).
  evidence:
  - reference: ORPHA:803
    reference_title: "Amyotrophic lateral sclerosis (Orphanet structured-database record)"
    supports: SUPPORT
    snippet: "1-9 / 100 000 | Europe | Annual incidence | PMID:19710046,EXPERT"
    explanation: Orphanet epidemiology table reports a European annual incidence of 1-9 per 100,000.
datasets:
- accession: gtex:GTEx_v8_Spinal_cord_cervical_c-1
  title: GTEx v8 Spinal Cord (cervical c-1)
  description: Bulk RNA-seq from healthy cervical spinal cord to provide baseline expression for upper and lower motor neuron pathways affected in ALS.
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_types:
  - preferred_term: spinal cord
    term:
      id: UBERON:0002240
      label: spinal cord
  publication: PMID:33085325
  evidence:
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "ALS is a neurodegenerative disorder leading to weakness of the bulbar, thoracic, limb, and abdominal muscles with sparing of sensory function."
    explanation: Clinical overview notes degeneration across spinal motor systems; spinal cord baseline controls contextualize transcriptomic changes in ALS.
- accession: gtex:GTEx_v8_Skeletal_Muscle
  title: GTEx v8 Skeletal Muscle
  description: Bulk RNA-seq from healthy skeletal muscle to benchmark ALS-related denervation signatures and muscle atrophy pathways.
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_types:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  publication: PMID:33085325
  evidence:
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "ALS is a neurodegenerative disorder leading to weakness of the bulbar, thoracic, limb, and abdominal muscles with sparing of sensory function."
    explanation: Muscle weakness and atrophy are primary clinical consequences in ALS; healthy muscle RNA-seq provides comparative background for ALS muscle involvement.
animal_models:
- species: Dog
  genotype: SOD1 c.118G>A (p.E40K) homozygous
  background: Pembroke Welsh Corgi, Boxer, Rhodesian Ridgeback, German Shepherd Dog,
    Chesapeake Bay Retriever
  description: >
    Canine degenerative myelopathy (DM) is a naturally occurring, adult-onset,
    fatal neurodegenerative disease caused by homozygosity for the SOD1 c.118G>A
    (p.E40K) missense mutation, identified across five breeds. Progressive upper
    motor neuron spastic ataxia in the pelvic limbs typically begins at 8 years
    or older, ascending to flaccid tetraparesis if euthanasia is delayed. Spinal
    cord histology reveals myelin and axon loss in the lateral white matter and
    neuronal cytoplasmic SOD1-immunoreactive inclusions mirroring human ALS
    pathology. This is the first recognized spontaneously occurring animal model
    for ALS.
  evidence:
  - reference: PMID:19188595
    reference_title: "Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Our findings identify canine DM to be the first recognized spontaneously occurring animal model for ALS."
    explanation: >
      Awano et al. 2009 identified the SOD1 E40K mutation in DM-affected dogs by
      genome-wide association mapping and demonstrated SOD1-immunoreactive
      cytoplasmic inclusions similar to human ALS pathology, formally establishing
      canine DM as the first spontaneous large-animal ALS model.
- species: Horse
  genotype: acquired (vitamin E deficiency / chronic oxidative stress)
  description: >
    Equine motor neuron disease (EMND) is a naturally occurring, acquired lower
    motor neuron disease of adult horses linked to chronic vitamin E deficiency
    and oxidative stress, arising in horses stabled without access to pasture.
    Clinical signs include progressive weight loss, muscle fasciculations, constant
    weight shifting in the rear limbs, abnormally low head carriage, and excessive
    recumbency. Pathological findings include type 1 muscle fibre atrophy and
    lipopigment accumulation in spinal cord capillary endothelium. Unlike classic
    ALS, which requires combined upper and lower motor neuron degeneration, EMND
    involves predominantly lower motor neurons (no upper motor neuron involvement),
    limiting direct phenotypic equivalence to human ALS.
  evidence:
  - reference: PMID:7988544
    reference_title: "Equine motor neuron disease: findings in 28 horses and proposal of a pathophysiological mechanism for the disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Pathological findings, preference of type 1 muscle fibre atrophy and lipopigment accumulation within the capillary endothelium of the spinal cord of all cases, supported the hypothesis of EMND being an oxidative disease."
    explanation: >
      Divers et al. 1994 described the clinical and pathological features of EMND
      in 28 horses and proposed oxidative stress as the pathophysiological
      mechanism, establishing this naturally occurring condition as a motor neuron
      disease analog.
  - reference: PMID:9373362
    reference_title: "Intrinsic, management, and nutritional factors associated with equine motor neuron disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The relationship of specific nutritional factors to EMND supports the hypothesis that a deficiency of vitamin E contributes to the disease."
    explanation: >
      de la Rúa-Domènech et al. 1997 identified vitamin E deficiency as a key
      risk factor for EMND in a case-control study of 87 affected horses and 259
      controls, reinforcing the oxidative stress pathophysiology.
differential_diagnoses:
- name: Chronic Inflammatory Demyelinating Polyradiculoneuropathy
  description: Immune-mediated demyelinating neuropathy causing progressive symmetric weakness and sensory loss; may mimic lower motor neuron-predominant ALS.
  disease_term:
    preferred_term: Chronic Inflammatory Demyelinating Polyradiculoneuropathy
    term:
      id: MONDO:0006702
      label: chronic inflammatory demyelinating polyradiculoneuropathy
  evidence:
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Some disorders that can mimic motor neuron disease are multifocal motor neuropathy with conduction block, chronic inflammatory demyelinating polyradiculoneuropathy, central nervous system tumors, multiple sclerosis, and polyradiculopathy, among others."
    explanation: StatPearls review lists CIDP among conditions that can mimic ALS and should be ruled out.
- name: Multiple Sclerosis
  description: Demyelinating disease of the central nervous system with motor weakness and spasticity that can resemble early ALS presentations.
  disease_term:
    preferred_term: multiple sclerosis
    term:
      id: MONDO:0005301
      label: multiple sclerosis
  evidence:
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Some disorders that can mimic motor neuron disease are multifocal motor neuropathy with conduction block, chronic inflammatory demyelinating polyradiculoneuropathy, central nervous system tumors, multiple sclerosis, and polyradiculopathy, among others."
    explanation: The same review identifies multiple sclerosis as a diagnostic mimic of motor neuron disease.
- name: Multifocal Motor Neuropathy
  description: Immune-mediated, asymmetric, distal motor neuropathy with conduction block that can present with focal weakness mimicking lower motor neuron ALS.
  disease_term:
    preferred_term: multifocal motor neuropathy
    term:
      id: MONDO:0018979
      label: multifocal motor neuropathy
  evidence:
  - reference: PMID:33085325
    reference_title: "Electrodiagnostic Evaluation of Motor Neuron Disease."
    supports: SUPPORT
    snippet: "Some disorders that can mimic motor neuron disease are multifocal motor neuropathy with conduction block, chronic inflammatory demyelinating polyradiculoneuropathy, central nervous system tumors, multiple sclerosis, and polyradiculopathy, among others."
    explanation: StatPearls review lists multifocal motor neuropathy with conduction block as an ALS mimic that must be ruled out.
discussions:
- discussion_id: gap_als_tdp43_selective_vulnerability_and_spread
  prompt: >-
    Which TDP-43-dependent RNA-processing defect, cytoplasmic aggregate species,
    or non-cell-autonomous signal explains why upper and lower motor neurons are
    selectively vulnerable in ALS, and how does this mechanism relate to clinical
    propagation across neuroanatomical regions?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - mechanistic_hypothesis#tdp43_rna_dysregulation_selective_vulnerability_model
  - pathophysiology#TDP-43 Proteinopathy
  - pathophysiology#TDP-43-Dependent Cryptic Exon Misprocessing
  - pathophysiology#Motor Neuron Degeneration
  rationale: >-
    STMN2 and UNC13A make TDP-43 loss-of-function concrete at the RNA target
    level, but they do not yet explain why particular motor-neuron classes
    degenerate while other neurons or glia with TDP-43 pathology can be less
    affected. Separating nuclear RNA loss-of-function from cytoplasmic
    gain-of-function and spread-like propagation is required to decide whether
    therapies should prioritize restoring individual transcripts, correcting
    TDP-43 localization, clearing aggregate species, or targeting glial and
    circuit-level amplifiers.
  proposed_experiments:
  - experiment_id: exp_als_isogenic_motor_neuron_tdp43_target_rescue_panel
    name: Isogenic human motor-neuron TDP-43 target rescue and spatial validation panel
    description: >-
      Compare isogenic human iPSC-derived upper- and lower-motor-neuron-like
      cultures with controlled nuclear TDP-43 depletion, TDP-43 cytoplasmic
      mislocalization, and patient-derived TDP-43 aggregate seeding. Rescue STMN2,
      UNC13A, and candidate transcript targets singly and in combination, then
      benchmark survival, axonal regeneration, synaptic function, lysosome
      trafficking, and spatial transcriptomic signatures against ALS postmortem
      motor cortex and spinal cord.
    experiment_type:
      preferred_term: isogenic stem-cell perturbation and spatial transcriptomics experiment
    decision_criterion: >-
      A causal RNA-processing target should rescue motor-neuron survival or
      axonal/synaptic function in TDP-43-deficient cells and show spatially
      concordant misprocessing in vulnerable human ALS motor-neuron populations;
      failure of target rescue would shift priority toward aggregate-seeding,
      proteostatic, glial, or circuit-level propagation mechanisms.
  evidence:
  - reference: PMID:37999738
    reference_title: "Selective vulnerability of motor neuron types and functional groups to degeneration in amyotrophic lateral sclerosis: review of the neurobiological mechanisms and functional correlates."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Despite extensive research, it remains unclear why some motor neurons are especially susceptible to the disease, while others are affected less or even spared."
    explanation: >
      Review explicitly frames motor-neuron selective vulnerability as an
      unresolved ALS mechanism.
  - reference: PMID:32799899
    reference_title: "The role of TDP-43 mislocalization in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Yet in ALS, motor neurons selectively degenerate suggesting that the presence of TDP-43 aggregates may not necessarily drive cell-death."
    explanation: >-
      TDP-43 review highlights the unresolved gap between aggregate presence and
      selective motor-neuron death.
- discussion_id: gap_als_tdp43_mislocalization_upstream_trigger
  prompt: >-
    What upstream cellular event triggers preferential TDP-43 nuclear
    clearance and cytoplasmic mislocalization in motor neurons compared with
    other cell types that also express TDP-43?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#TDP-43 Proteinopathy
  - mechanistic_hypothesis#tdp43_rna_dysregulation_selective_vulnerability_model
  rationale: >-
    TDP-43 is a ubiquitously expressed nuclear RNA-binding protein, yet in ALS
    it mislocalizes and aggregates preferentially in motor neurons. The NLS and
    NES sequences of TDP-43 are not motor-neuron specific, and cellular
    stressors such as oxidative stress, osmotic stress, or heat shock can
    induce phase-separated TDP-43 cytoplasmic structures in many cell types.
    What makes motor neurons uniquely susceptible to irreversible TDP-43
    mislocalization — whether through long-axon-specific transport burdens,
    particular importin isoform expression, differential proteostatic capacity,
    or a specific upstream metabolic vulnerability — is not established.
    Identifying this upstream trigger is required to explain why ALS is a
    motor-neuron disease rather than a pan-neuronal or pan-cellular
    proteinopathy, and to determine the earliest actionable intervention point.
  evidence:
  - reference: PMID:32799899
    reference_title: "The role of TDP-43 mislocalization in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The exact mechanisms mediating the formation of TDP-43 aggregates remain elusive."
    explanation: >-
      Review acknowledges that the upstream trigger for TDP-43 aggregation
      and mislocalization is unresolved, supporting this as an open knowledge
      gap distinct from the downstream RNA-processing defects.
  - reference: PMID:37999738
    reference_title: "Selective vulnerability of motor neuron types and functional groups to degeneration in amyotrophic lateral sclerosis: review of the neurobiological mechanisms and functional correlates."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Despite extensive research, it remains unclear why some motor neurons are especially susceptible to the disease, while others are affected less or even spared."
    explanation: >-
      Selective vulnerability review frames the motor-neuron-preferential
      degeneration as unresolved, implicating upstream cell-type-specific
      factors in TDP-43 mislocalization as a key open question.
- discussion_id: gap_als_ptdp43_propagation_mechanism
  prompt: >-
    Does phosphorylated TDP-43 pathology spread through the ALS motor
    system by prion-like protein seeding, by trans-synaptic or retrograde
    axonal signaling, or by secondary neuroinflammatory relay — and can
    these mechanisms be distinguished experimentally?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#TDP-43 Proteinopathy
  - pathophysiology#Motor Neuron Degeneration
  - mechanistic_hypothesis#tdp43_rna_dysregulation_selective_vulnerability_model
  rationale: >-
    Cross-sectional postmortem staging studies show that pTDP-43 pathology
    progresses through the ALS motor system in a stereotyped, anatomically
    sequential pattern analogous to Braak staging in Parkinson disease and
    Alzheimer disease, consistent with a propagating process. However, the
    cellular mechanism of spread is not established: whether pTDP-43
    propagates by direct cell-to-cell protein seeding (prion-like templating),
    by trans-synaptic or retrograde axonal transport of a pathological signal,
    by secondary glial or neuroinflammatory relay, or by some combination of
    these mechanisms remains unresolved. Understanding the propagation
    mechanism has direct therapeutic implications — a seeding model prioritizes
    aggregate clearance or passive immunotherapy at early disease stages, while
    an inflammatory-relay model prioritizes anti-neuroinflammatory intervention
    at transitional anatomical boundaries.
  evidence:
  - reference: PMID:23686809
    reference_title: "Stages of pTDP-43 pathology in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "pTDP-43 pathology in ALS possibly disseminates in a sequential pattern that permits recognition of 4 neuropathological stages consistent with the hypothesis that pTDP-43 pathology is propagated along axonal pathways."
    explanation: >-
      Postmortem staging data in 76 ALS cases support sequential anatomical
      spread of pTDP-43 pathology, motivating the mechanistic question of how
      this propagation is achieved without establishing the cellular mechanism.
  - reference: PMID:23686809
    reference_title: "Stages of pTDP-43 pathology in amyotrophic lateral sclerosis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Whereas the cell-to-cell transmission of pTDP-43 has not been demonstrated conclusively in vivo, a recently discovered C-terminal prion-like domain has been implicated in the aggregation of pTDP-43 in cultured cells."
    explanation: >-
      In vitro prion-like domain evidence is consistent with protein seeding
      but does not establish in vivo cell-to-cell transmission, leaving the
      propagation mechanism open.
- discussion_id: mismatch_emnd_lmn_only_phenotype
  prompt: >-
    Does the lower-motor-neuron-only phenotype of equine motor neuron disease
    (EMND) preclude its use as a model for classic ALS, which requires both upper
    and lower motor neuron degeneration?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - animal_model#Horse
  rationale: >-
    Classic ALS is defined by combined upper motor neuron (UMN) and lower motor
    neuron (LMN) degeneration. Equine motor neuron disease (EMND) involves
    predominantly or exclusively lower motor neurons, with no established
    corticospinal tract involvement, making it a phenotypically closer analog to
    progressive muscular atrophy (LMN-only ALS variant) than to classic ALS.
    This reduces the direct translational value of EMND as an ALS model, though
    the shared oxidative stress mechanism and spinal motor neuron vulnerability
    retain biological relevance for the LMN degenerative arm of the disease.
  proposed_experiments:
  - experiment_id: exp_emnd_umn_tract_assessment
    name: Corticospinal tract histopathological survey in EMND horses
    description: >-
      Systematic immunohistochemical and histopathological assessment of
      corticospinal tracts and motor cortex in post-mortem EMND horses to
      determine whether subclinical UMN pathology is present but overlooked in
      existing case series, or is genuinely absent.
    experiment_type:
      preferred_term: post-mortem neuropathological study
    decision_criterion: >-
      Detection of UMN pathology would support EMND as a true ALS analog;
      confirmed absence would classify EMND as a selective LMN disease and
      redirect its value to studies of the ALS LMN degenerative arm only.

📚

References & Deep Research

Deep Research

Claude Code ▸

1. Disease Information

claude-haiku-4-5-20251001, claude-opus-4-8[1m] 12 citations 2026-07-09T16:06:31.461403

1. Disease Information

Overview. Amyotrophic lateral sclerosis (ALS), also called motor neuron disease (MND) in the UK/Commonwealth and "Lou Gehrig's disease" in the US, and maladie de Charcot in France, is a progressive, fatal neurodegenerative disorder characterized by the combined degeneration of upper motor neurons (UMN; Betz cells of the primary motor cortex and the corticospinal tracts) and lower motor neurons (LMN; anterior horn cells of the spinal cord and brainstem motor nuclei). The result is progressive muscle weakness, atrophy, spasticity, and ultimately paralysis, with death most commonly from neuromuscular respiratory failure, typically 2–4 years after symptom onset. ALS exists on a clinical–pathological continuum with frontotemporal dementia (FTD); up to ~50% of patients have some cognitive/behavioral impairment and ~13–15% meet criteria for concomitant FTD (Brown & Al-Chalabi, N Engl J Med 2017, PMID:28700839; van Es et al., Lancet 2017 seminar, PMID:28552366; Feldman et al., Lancet 2022, PMID:36116464).

Key identifiers. - MONDO: MONDO:0004976 (amyotrophic lateral sclerosis); locus-specific children include MONDO:0007103 (ALS1, SOD1). - OMIM: #105400 (ALS1, SOD1); phenotypic series PS105400 enumerates ALS1–ALS26+ loci. C9orf72 ALS-FTD = #105550 (FTDALS1). - Orphanet: ORPHA:803 (amyotrophic lateral sclerosis). - ICD-10: G12.21. ICD-11: 8B60.0. - MeSH: D000690 (Amyotrophic Lateral Sclerosis); tree under "Motor Neuron Disease" (D016472). - UMLS/SNOMED CT: 86044005 (Amyotrophic lateral sclerosis).

Synonyms / alternative names. Motor neuron disease (MND); Lou Gehrig's disease; Charcot disease; classic/classical ALS. Related MND phenotypes that some classifications group with ALS: primary lateral sclerosis (PLS) (pure UMN), progressive muscular atrophy (PMA) (pure LMN), progressive bulbar palsy (PBP) (bulbar-onset), and the ALS-FTD spectrum.

Data provenance. The KB entry should be built from aggregated disease-level resources (OMIM, Orphanet, HPO, systematic reviews, natural-history registries such as PRO-ACT, and society guidelines), not individual EHR/patient records. Genetic frequencies are drawn from familial cohorts and population databases (gnomAD, Project MinE).

2. Etiology

ALS is etiologically heterogeneous. ~90% of cases are sporadic (sALS); ~10% are familial (fALS), usually autosomal dominant. Even sporadic ALS has a substantial genetic contribution (twin-study heritability ~0.4–0.6) and is best modeled as a gene–environment, multistep process (Al-Chalabi et al., Lancet Neurol 2014 multistep model, PMID:24507800 — estimated a six-step process).

Primary causal factors. - Genetic (monogenic and oligogenic). Four genes dominate: C9orf72, SOD1, TARDBP, FUS. Together they explain up to ~60–70% of fALS and ~10% of sALS in European populations (see §4). C9orf72 hexanucleotide expansion is the single most common cause overall. - Convergent molecular mechanism. Regardless of trigger, >97% of ALS cases share cytoplasmic TDP-43 (TARDBP) mislocalization and aggregation as the pathological signature; the principal exceptions are SOD1- and FUS-mutant cases, which have SOD1- or FUS-positive/TDP-43-negative inclusions (Neumann et al., Science 2006, PMID:17023659 — identified TDP-43 as the ubiquitinated inclusion protein).

Risk factors.

Genetic risk / susceptibility. - C9orf72 G4C2 repeat expansion (>~30 repeats pathogenic; intermediate alleles debated) — largest single genetic risk factor; incomplete, age-dependent penetrance. - ATXN2 intermediate-length polyQ repeats (~27–33 CAG) — validated risk factor for sporadic ALS (Elden et al., Nature 2010, PMID:20740007). - SOD1, TARDBP, FUS rare variants (see §4). UNC13A polymorphisms modify risk and survival. - Rare-variant burden in TBK1, NEK1, KIF5A, C21orf2, OPTN, VCP, UBQLN2, CHCHD10, MATR3, PFN1, ANXA11, TIA1, SQSTM1, TUBA4A.

Environmental / demographic risk. - Age (peak onset 55–75) and male sex (M:F ~1.3–1.5:1, converging after menopause). - Family history of ALS/FTD. - Cigarette smoking — the most consistently replicated exogenous risk factor (probable causal; especially in women). - Physical activity / elite athleticism & professional sport (e.g., Italian football, US football) and military service — associated in multiple cohorts, though confounding and reverse-causation debated. - Occupational/environmental exposures: heavy metals (lead), pesticides/agrochemicals, electromagnetic fields, formaldehyde — associations of variable strength. - β-methylamino-L-alanine (BMAA), a cyanobacterial neurotoxin, implicated in the Western Pacific ALS–Parkinsonism–dementia complex (Guam ALS-PDC) (Cox et al. hypothesis; contested).

Protective factors. - Higher BMI / hyperlipidemia are consistently associated with lower risk and better survival (a metabolic-reserve effect) — one of the most robust epidemiological signals. - Type 2 diabetes associated with reduced ALS risk in European populations (opposite in Asian populations). - Genetic protective/modifier alleles remain an active area; no well-established protective coding variant analogous to APOE exists.

Gene–environment interaction. The multistep model implies that inherited variants "use up" one or more of the ~6 steps, so mutation carriers require fewer environmental hits and present earlier — e.g., C9orf72 carriers show a lower estimated step number than sporadic patients (Al-Chalabi et al., PMID:24507800; Vucic et al. multistep replication studies).

3. Phenotypes

ALS phenotypes span motor (UMN + LMN), bulbar, respiratory, cognitive/behavioral, and constitutional domains. Suggested HPO terms (verify labels with OAK before KB entry):

Phenotype	Domain	Typical frequency	Suggested HPO
Progressive muscle weakness	LMN/UMN	Universal (obligate)	HP:0003323 (Progressive muscle weakness)
Skeletal muscle atrophy / amyotrophy	LMN	Very frequent	HP:0003202 (Skeletal muscle atrophy)
Fasciculations	LMN	Very frequent	HP:0002380 (Fasciculations)
Muscle cramps	LMN	Frequent (early)	HP:0003394 (Muscle cramps)
Spasticity	UMN	Frequent	HP:0001257 (Spasticity)
Hyperreflexia	UMN	Frequent	HP:0001347 (Hyperreflexia)
Dysarthria	Bulbar UMN/LMN	Frequent	HP:0001260 (Dysarthria)
Dysphagia	Bulbar	Frequent	HP:0002015 (Dysphagia)
Sialorrhea / drooling	Bulbar	Frequent	HP:0002307 (Drooling)
Tongue atrophy & fasciculations	Bulbar LMN	Frequent	HP:0000167 (region) / fasciculation term
Respiratory insufficiency / failure	Respiratory	Terminal (cause of death)	HP:0002093 / HP:0002878 (Respiratory failure)
Dyspnea, orthopnea	Respiratory	Frequent (late)	HP:0002094 (Dyspnea)
Weight loss / hypermetabolism	Constitutional	Frequent	HP:0001824 (Weight loss)
Pseudobulbar affect (emotional lability)	Behavioral	~20–50%	HP:0000749 (Emotional lability)
Frontotemporal dementia	Cognitive	~13–15%	HP:0002145 (Frontotemporal dementia)
Executive/behavioral cognitive impairment (sub-FTD)	Cognitive	Up to ~50%	HP:0100543 (Cognitive impairment)
Preserved sensation / oculomotor / sphincter (typical sparing)	—	Characteristic	(document as negative features)

Onset topography. ~⅔ spinal (limb) onset (asymmetric distal limb weakness — foot drop, hand clumsiness/split-hand), ~⅓ bulbar onset (dysarthria/dysphagia; more common in older women, worse prognosis), and a minority respiratory-onset (worst prognosis). "Flail arm" (Vulpian-Bernhardt) and "flail leg" variants and PLS/PMA represent phenotypic extremes.

Characteristics. Adult onset (median ~58–63 y; earlier in fALS, especially SOD1/FUS which can be juvenile). Course is relentlessly progressive with contiguous anatomical spread from the onset region. Severity variable but uniformly disabling.

Quality-of-life impact. Progressive loss of ambulation → wheelchair dependence; loss of speech → augmentative/alternative communication; loss of swallow → gastrostomy dependence and aspiration risk; respiratory decline → ventilatory dependence; retained cognition in most patients means awareness of decline (high depression/existential distress). Measured with ALSFRS-R (function), ALSAQ-40/ALSAQ-5 (disease-specific QoL), and generic EQ-5D/SF-36.

4. Genetic / Molecular Information

Causal genes (the "big four" + long tail; OMIM phenotypic series PS105400).

Gene	HGNC	ALS locus / OMIM	% fALS	% sALS	Inheritance	Dominant mechanism
C9orf72	hgnc:28337	FTDALS1 #105550	~30–40%	~5–7%	AD	GGGGCC intronic expansion; RNA foci + DPR (RAN translation) + haploinsufficiency (GoF+LoF)
SOD1	hgnc:11179	ALS1 #105400	~12–20%	~1–2%	AD (rare AR, e.g., D90A)	Misfolded-protein toxic gain of function
TARDBP (TDP-43)	hgnc:11571	ALS10 #612069	~4–5%	~1%	AD	RNA-binding dysfunction; aggregation
FUS	hgnc:4010	ALS6 #608030	~4%	~1%	AD (juvenile)	RNA/DNA-binding; cytoplasmic aggregation
TBK1	hgnc:11584	ALS/FTD	~1–2%	—	AD	Haploinsufficiency; autophagy/inflammation
KIF5A	hgnc:6323	ALS25	~1%	—	AD	Splice/C-terminal; axonal transport
NEK1, C21orf2, OPTN, VCP, UBQLN2, CHCHD10, MATR3, PFN1, ANXA11, TIA1, SQSTM1, TUBA4A, DCTN1, SETX, ALS2, SPG11, FIG4	—	ALS2–ALS26	rare	rare	AD/AR/XL	Autophagy, proteostasis, cytoskeleton, mitochondria, RNA metabolism

Landmark gene-discovery citations: - SOD1 — Rosen et al., Nature 1993 (first ALS gene), PMID:8446170. - TARDBP/TDP-43 mutations — Sreedharan et al., Science 2008, PMID:18309045. - FUS — Kwiatkowski et al., Science 2009, PMID:19251627; Vance et al., Science 2009, PMID:19251628. - C9orf72 G4C2 expansion — DeJesus-Hernandez et al., Neuron 2011, PMID:21944778; Renton et al., Neuron 2011, PMID:21944779. - UBQLN2 (X-linked) — Deng et al., Nature 2011, PMID:21857683. - TBK1 — Freischmidt et al., Nat Neurosci 2015, PMID:26192745. - KIF5A — Nicolas et al., Neuron 2018, PMID:29566793.

Pathogenic variants — classification & type. - SOD1: >180 mostly missense variants (e.g., p.Ala5Val/A4V — aggressive, N. American; p.Asp91Ala/D90A — often recessive, slowly progressive, Scandinavian; p.Gly94Ala/G93A — the canonical mouse model allele). ACMG classification: many pathogenic/likely pathogenic in ClinVar. Mechanism = toxic gain of function (misfolding), not loss of dismutase activity. - C9orf72: noncoding GGGGCC hexanucleotide repeat expansion in intron 1 (normal <~24; pathogenic hundreds–thousands). Repeat-primed PCR / Southern blot required (not standard NGS). - TARDBP/FUS: predominantly missense clustered in the glycine-rich/low-complexity C-terminal domain (TDP-43) and the C-terminal NLS/RGG region (FUS). - KIF5A: loss-of-splice-site / C-terminal variants.

Allele frequency / somatic vs germline. ALS variants are germline; SOD1/TARDBP/FUS pathogenic alleles are essentially absent/ultra-rare in gnomAD controls, consistent with pathogenicity. C9orf72 expansions are not captured by standard population SNV databases. Somatic mosaicism is described (e.g., FUS) but rare.

Modifier genes. ATXN2 intermediate repeats (risk + earlier onset; PMID:20740007); UNC13A (survival/cognition modifier and a cryptic-exon target of TDP-43 loss); EPHA4 (survival); KIFAP3, CAMTA1 (reported modifiers).

Epigenetics. C9orf72 promoter/repeat hypermethylation can reduce expression and modestly protect; global and locus-specific DNA-methylation changes and histone modifications at C9orf72 reported (search ENCODE/Roadmap; DiseaseMeth). Epigenetic DNA methylation "clocks" show accelerated biological aging in ALS.

Chromosomal abnormalities. The C9orf72 repeat maps to chromosome 9p21; ALS is otherwise not a large-CNV/aneuploidy disorder. Large structural variants are rare contributors.

5. Environmental Information

Toxins / occupational exposures (search CTD): lead and other heavy metals, pesticides/organochlorines, agrochemicals, solvents/formaldehyde, and cyanotoxin BMAA (CHEBI candidate; Guam ALS-PDC). Electromagnetic-field/electric-shock exposure hypothesized.
Lifestyle: cigarette smoking (probable causal risk); vigorous/high-level physical activity and contact/professional sport; military deployment (Gulf War veterans). High premorbid BMI/lipids protective (§2).
Infectious agents: No established infectious cause. Human endogenous retrovirus HERV-K (HML-2) reactivation has been proposed as a mechanistic contributor (TDP-43 can transactivate HERV-K), motivating antiretroviral trials (e.g., Triumeq/Lighthouse); enteroviral hypotheses unconfirmed. This is best curated as a hypothesis/knowledge-gap, not established etiology.

6. Mechanism / Pathophysiology

ALS is a convergent, multi-mechanism motor-neuron proteinopathy. The dominant unifying lesion is nuclear clearance and cytoplasmic aggregation of TDP-43, causing both loss of nuclear RNA-processing function and cytoplasmic gain of toxicity (Neumann et al., PMID:17023659; reviews Taylor, Brown & Ravits, Nature 2016 "Decoding ALS," PMID:27830784).

Causal chain (upstream → downstream), with GO/CL suggestions:

Genetic/environmental trigger (mutation, aging, oxidative burden) →
RNA-metabolism dysregulation & TDP-43/FUS mislocalization — impaired splicing, mRNA transport, stress-granule dynamics; loss of TDP-43 nuclear function → cryptic-exon inclusion (e.g., in STMN2 and UNC13A), a key emerging mechanism.
GO:0008380 (RNA splicing); GO:0006406 (mRNA export from nucleus); GO:0010494 (cytoplasmic stress granule); GO:0006913 (nucleocytoplasmic transport).
Proteostasis failure & protein aggregation — misfolded SOD1, TDP-43, FUS, DPR aggregates; impaired autophagy and ubiquitin–proteasome clearance (OPTN, SQSTM1, UBQLN2, VCP, TBK1 converge here).
GO:0006914 (autophagy); GO:0000045 (autophagosome assembly); GO:0043161 (proteasome-mediated ubiquitin-dependent protein catabolic process); GO:0031625 (ubiquitin protein ligase binding).
Nucleocytoplasmic transport defects — C9orf72 DPRs (esp. arginine-rich poly-GR/PR) disrupt the nuclear pore.
C9orf72-specific triad: (a) RNA foci sequestering RNA-binding proteins; (b) RAN-translated dipeptide repeat proteins (poly-GA, -GP, -GR, -PR, -PA) that are toxic (Mori et al., Science 2013, PMID:23393093; Ash et al., Neuron 2013, PMID:23415312); (c) C9orf72 haploinsufficiency impairing autophagy/immune function.
Glutamate excitotoxicity — deficient astrocytic EAAT2/GLT-1 glutamate uptake → excess synaptic glutamate → Ca²⁺-mediated excitotoxic motor-neuron injury (the rationale for riluzole).
GO:0051966 (regulation of glutamatergic synaptic transmission); CHEBI:14321 (glutamate); CHEBI:29108 (calcium).
Mitochondrial dysfunction & oxidative stress — impaired bioenergetics, ROS; SOD1 links directly (though toxicity is misfolding-driven, not enzyme loss).
GO:0006979 (response to oxidative stress); GO:0004784 (superoxide dismutase activity); CHEBI:18421 (superoxide); CHEBI:16240 (hydrogen peroxide).
Axonal transport & cytoskeletal defects — KIF5A, DCTN1, PFN1, TUBA4A, NEFH; distal ("dying-back") axonopathy and neuromuscular-junction denervation as an early event.
Non–cell-autonomous neuroinflammation — reactive astrocytes and microglia drive progression; mutant SOD1 in glia accelerates disease independent of neuronal SOD1 (Boillée et al., Science 2006, microglial contribution, PMID:16741123).
GO:0150076 (neuroinflammatory response); GO:0006954 (inflammatory response); CL:0000129 (microglial cell); CL:0000127 (astrocyte).
Motor-neuron degeneration & apoptosis → denervation → muscle atrophy/paralysis → respiratory failure.
- GO:0043065 (positive regulation of apoptotic process); CL:0000100 (motor neuron); CL:0011001 (spinal cord motor neuron); CL:0000598 (pyramidal neuron, for corticomotoneurons).

Prion-like spread. Misfolded SOD1 and TDP-43 propagate template-directed misfolding cell-to-cell, consistent with the clinically observed contiguous anatomical spread from the onset focus.

Protein dysfunction detail. SOD1 = destabilized/misfolded metalloenzyme (Cu/Zn) forming toxic oligomers (UniProt P00441). TDP-43 (UniProt Q13148) and FUS (UniProt P35637) are RNA/DNA-binding proteins with low-complexity/prion-like domains that drive aberrant liquid–liquid phase separation into pathological solid aggregates.

Molecular profiling. Transcriptomics of ALS motor cortex/spinal cord (GEO datasets) show splicing dysregulation and cryptic exons; single-nucleus RNA-seq reveals selective vulnerability and glial activation states; CSF/plasma neurofilament (NfL, pNfH) is the leading fluid proteomic biomarker (see §10). CRISPR functional-genomics screens (DepMap-style, and DPR-toxicity screens) implicate nucleocytoplasmic-transport and ER-stress modifiers.

7. Anatomical Structures Affected

Organ / system level. Primary target = the motor system of the central and peripheral nervous system. - Primary motor cortex / precentral gyrus (Betz cells) — UBERON:0001384 (primary motor cortex); UBERON:0002026 (precentral gyrus). - Corticospinal (pyramidal) tract / lateral corticospinal tract — UBERON:0002718 (lateral corticospinal tract). - Spinal cord anterior (ventral) horn — UBERON:0002240 (spinal cord); ventral/anterior horn gray matter. - Brainstem motor nuclei (hypoglossal, facial, trigeminal motor) — bulbar involvement. - Frontotemporal cortex — in ALS-FTD (UBERON:0001870 frontal cortex; UBERON:0001871 temporal lobe). - Secondary: skeletal muscle (denervation atrophy; UBERON:0001134 skeletal muscle tissue), diaphragm (UBERON:0001103) → respiratory system; downstream complications in respiratory and GI (aspiration) systems.

Characteristically spared (important negative features for KB): extraocular muscles/oculomotor neurons, Onuf's nucleus (sphincter/continence), sensory pathways, and autonomic function — usually preserved until very late.

Tissue / cell level. - Lower motor neurons — CL:0011001 (spinal cord motor neuron); CL:0000100 (motor neuron). - Upper motor neurons / Betz cells (corticomotoneurons) — CL:0000598 (pyramidal neuron). - Astrocytes — CL:0000127; microglia — CL:0000129; oligodendrocytes — CL:0000128 (contribute to non-cell-autonomous injury). - Skeletal muscle fiber — CL:0000188 (denervated).

Subcellular level (GO cellular component). Cytoplasmic inclusions (GO:0005737 cytoplasm); stress granules (GO:0010494); nucleus/nuclear clearance of TDP-43 (GO:0005634); mitochondrion (GO:0005739); neuromuscular junction (GO:0031594); nuclear pore/envelope (GO:0005643).

Localization / lateralization. Onset is characteristically focal and asymmetric (one limb), with contiguous ipsilateral and contralateral spread; the split-hand sign (preferential thenar/first-dorsal-interosseous wasting) is a recognized focal LMN pattern.

8. Temporal Development

Onset. Adult, typically 55–75 y (median ~58–63); insidious, focal, painless weakness. Juvenile/early-onset forms occur with FUS, SOD1, ALS2, SETX, SPG11.

Progression & staging. Relentlessly progressive; rate is variable but individually near-linear on ALSFRS-R. Two validated clinical staging systems: - King's staging (anatomical spread: stages 1–4A/4B by number of regions involved + gastrostomy/NIV milestones) — Roche et al., Brain 2012, PMID:22042175. - MiToS staging (functional loss across 4 domains) — Chiò et al., 2015.

Rate / course. Median survival ~2–4 years from symptom onset (from diagnosis shorter). Course is progressive, non-remitting (no relapsing-remitting phase; spontaneous remission essentially unknown/"reversal" cases extraordinarily rare and debated).

Prognostic tempo determinants (see §11): bulbar/respiratory onset, older age, short diagnostic delay (fast progression), FTD, low FVC, high ΔALSFRS-R slope, low BMI → faster. PLS and flail-limb variants, SOD1-D90A, and young onset → slower (survival can be many years to decades).

Critical intervention windows. Early NfL-guided and genetically-guided treatment initiation (tofersen data suggest earlier = better). Presymptomatic intervention is now being tested (ATLAS trial: tofersen in presymptomatic SOD1 carriers with rising NfL).

9. Inheritance and Population

Epidemiology. - Incidence: ~1.5–2.7 per 100,000 person-years in European-ancestry populations (Europe age-standardized ~1.0–2.6/100,000/yr); lower reported rates in East Asian and admixed populations. US age-adjusted incidence ~1.5–1.7/100,000 (recent CDC/registry data). - Prevalence: ~4.5–9 per 100,000; a 2023 systematic review/model projects global prevalence rising substantially by 2040 with population aging (Global prevalence & incidence systematic review, Neurology 2023 — see PMC10424837 / DOI 10.1212/WNL.0000000000207474). Registry-based projections (Italy) estimate prevalence ~11.7/100,000 in 2024 rising toward ~15.7/100,000 by 2040. - Lifetime risk ~1 in 300–400.

Inheritance & genetic-counseling parameters. - Pattern: Predominantly autosomal dominant in fALS (SOD1, C9orf72, TARDBP, FUS, TBK1, KIF5A); X-linked (UBQLN2); autosomal recessive (some SOD1-D90A, ALS2/alsin, SPG11); and multifactorial/oligogenic/polygenic in sporadic disease. - Penetrance: Incomplete and age-dependent — notably C9orf72 (near-complete only by ~80 y) and SOD1 (allele-dependent; A4V high, D90A variable/recessive). ATXN2 = risk factor, not fully penetrant. - Expressivity: Highly variable — same C9orf72 expansion can yield pure ALS, pure FTD, or ALS-FTD within one family. - Anticipation: C9orf72 shows repeat instability and some evidence of anticipation, but it is not a classic clean anticipation disorder. - Oligogenic inheritance: Increasingly recognized (e.g., co-occurring C9orf72 + ATXN2 or + TBK1 variants worsen/modify phenotype) — relevant to the dismech digenic/oligogenic curation pattern. - Founder effects: SOD1-D90A (Scandinavian/Finnish recessive founder haplotype); C9orf72 shares a common founder haplotype across European populations. - Consanguinity: relevant for recessive juvenile forms (ALS2, SPG11) in consanguineous populations.

Population demographics. Higher measured burden in European-ancestry populations; male predominance (M:F ~1.2–1.5:1, attenuating with age). Geographic clusters historically: Western Pacific ALS-PDC (Guam Chamorro, Kii Peninsula Japan, West Papua) — declining, environmentally linked.

10. Diagnostics

ALS is a clinical diagnosis (UMN + LMN signs, progressive spread, exclusion of mimics) supported by electrophysiology; no single confirmatory test.

Diagnostic criteria. - Gold Coast criteria (2020/2021) — current consensus; simplified dichotomous (ALS vs not-ALS), higher sensitivity (~93–96%) than revised El Escorial (Airlie House) and Awaji-shima criteria (Shefner et al., Clin Neurophysiol 2020, PMID:32410883). - Prior systems: revised El Escorial, Awaji (incorporates EMG as clinical-equivalent).

Electrophysiology (core). Needle EMG shows active + chronic denervation/reinnervation (fibrillations, positive sharp waves, fasciculation potentials, large/unstable motor units) in ≥2 body regions; nerve conduction studies exclude conduction block/neuropathy; motor unit number estimation (MUNE) and transcranial magnetic stimulation (threshold tracking → cortical hyperexcitability) as research/supportive tools.

Laboratory & biomarkers. - Neurofilaments — the key fluid biomarker: elevated serum/CSF neurofilament light chain (NfL) and phosphorylated neurofilament heavy chain (pNfH) support diagnosis, correlate with progression rate, and are used as pharmacodynamic/prognostic markers. NfL reduction was the surrogate endpoint for tofersen's accelerated approval (Miller et al., N Engl J Med 2022 VALOR, PMID:36170501). - Routine labs to exclude mimics: CK (mildly elevated), TSH, PTH, serum protein electrophoresis, anti-GM1 (to exclude multifocal motor neuropathy), HIV, Lyme, heavy metals, hexosaminidase A, VLCFA, CSF. - LOINC codes exist for NfL and the exclusionary panel.

Imaging. MRI brain/spinal cord primarily to exclude structural mimics (cervical spondylotic myelopathy, structural lesions); may show corticospinal-tract T2/FLAIR hyperintensity and motor-cortex "iron" hypointensity. Advanced DTI/functional MRI and PET (e.g., TSPO neuroinflammation) are research tools.

Genetic testing. Increasingly standard given gene-targeted therapy: at minimum C9orf72 repeat-primed PCR and SOD1 sequencing (therapeutically actionable), plus ALS gene panels / exome (TARDBP, FUS, TBK1, etc.). Testing now recommended for all ALS patients per updated consensus (actionability + trial eligibility + reproductive counseling). C9orf72 requires repeat-expansion testing (not captured by standard NGS).

Pathology (confirmatory at autopsy). Loss of anterior-horn and Betz cells; ubiquitin/p62-positive, TDP-43-positive cytoplasmic inclusions (Bunina bodies, skein-like inclusions); TDP-43 immunohistochemistry (Neumann et al., PMID:17023659). SOD1- and FUS-cases are TDP-43-negative.

Differential diagnosis. Multifocal motor neuropathy with conduction block, cervical spondylotic myelopathy, inclusion-body myositis, Kennedy disease (SBMA), spinal muscular atrophy, myasthenia gravis, ALS mimics (paraneoplastic, thyrotoxic), and monomelic amyotrophy (Hirayama).

Screening. No population screening. Cascade genetic testing / presymptomatic testing offered in known-mutation families (with counseling); presymptomatic NfL monitoring is emerging in SOD1 carriers (ATLAS).

11. Outcome / Prognosis

Survival: median ~2–4 years from symptom onset; ~50% die within 30 months of onset; ~10–20% survive >5 years, ~5–10% >10 years. Respiratory failure is the leading cause of death.
Mortality: essentially a uniformly fatal disease; disease-specific mortality dominates.
Prognostic factors (worse): bulbar or respiratory onset, older age at onset, short diagnosis delay / steep ALSFRS-R slope, low/declining FVC, low BMI and weight loss, cognitive impairment/FTD, high baseline NfL. Better: limb onset, young age, PLS/flail variants, SOD1-D90A, high BMI. The validated ENCALS survival model integrates these predictors.
Morbidity / disability: progressive tetraparesis, anarthria, dysphagia (malnutrition, aspiration pneumonia), ventilatory dependence, communication loss, and (in a subset) dementia — profound disability captured by ICF and ALSFRS-R.
QoL measures: ALSAQ-40/-5, EQ-5D, SF-36; caregiver burden is high.
Prognostic biomarkers: NfL/pNfH (rate + survival), ALSFRS-R slope, FVC/SNIP, and genotype (C9orf72 → shorter survival + FTD risk).

12. Treatment

No cure; management is multidisciplinary and largely disease-modifying-modest + supportive. Multidisciplinary ALS-clinic care itself improves survival and QoL (MAXO:0000950 supportive care; multidisciplinary care).

Disease-modifying pharmacotherapy. - Riluzole (CHEBI:8863) — anti-glutamatergic (Na⁺-channel/glutamate-release inhibitor). First and only globally licensed drug; prolongs survival/time-to-tracheostomy by ~2–3 months (Bensimon et al., N Engl J Med 1994, PMID:8302340). Oral tablet, liquid, and film formulations. MAXO: pharmacotherapy. - Edaravone (CHEBI:31530) — free-radical scavenger; IV and oral; slowed ALSFRS-R decline in a defined early-stage subgroup (Writing Group/Edaravone ALS-19 Study Group, Lancet Neurol 2017, PMID:28522181). Benefit debated; approved in US/Japan/others, not by EMA. - Tofersen (Qalsody) — antisense oligonucleotide (ASO), RNase-H knockdown of SOD1 mRNA; intrathecal. FDA accelerated approval April 2023 for SOD1-ALS — the first therapy targeting a genetic cause of ALS, approved on NfL reduction as surrogate; VALOR + open-label extension (Miller et al., N Engl J Med 2022, PMID:36170501). This maps directly to the dismech antisense_oligonucleotide_therapy module (RNase-H arm, target_gene SOD1) and therapeutic_modality: ANTISENSE_OLIGONUCLEOTIDE, aso_mechanism: RNASE_H_KNOCKDOWN. - Sodium phenylbutyrate/taurursodiol (AMX0035, Relyvrio/Albrioza) — approved 2022, then withdrawn from market in 2024 after the confirmatory PHOENIX phase 3 failed. Curate as historical/withdrawn (important accuracy point).

Pharmacogenomics / precision. SOD1 and C9orf72 genotype now gate therapy (tofersen for SOD1; investigational C9orf72 ASOs). This is genotype-guided precision neurology.

Advanced / investigational therapeutics. - C9orf72-targeted ASOs (e.g., BIIB078 — failed; afinersen; next-generation candidates) and RNA-targeting/gene therapies. - Gene therapy / gene editing (AAV-delivered, CRISPR) for SOD1/C9orf72 — preclinical/early clinical. - Cell therapy — mesenchymal stromal cell (NurOwn/debamestrocel — failed primary endpoint; FDA rejected), neural progenitor approaches. - Other trials: HERV-K antiretrovirals (Triumeq), CuATSM, pridopidine, DNL343 (integrated stress-response inhibitor), tofersen presymptomatic (ATLAS), masitinib, ANX005, and platform trials (HEALEY ALS Platform Trial, MND-SMART, TRICALS).

Symptomatic / supportive care (core of management). - Respiratory: non-invasive ventilation (NIV) improves survival and QoL (Bourke et al., Lancet Neurol 2006, PMID:16488378); tracheostomy/invasive ventilation as chosen; cough-assist/secretion management. MAXO: mechanical ventilation / respiratory therapy. - Nutrition: percutaneous endoscopic gastrostomy (PEG) for dysphagia/weight maintenance; high-calorie diet (MAXO: gastrostomy / dietary intervention MAXO:0000088). - Sialorrhea: anticholinergics, botulinum toxin, salivary-gland radiotherapy. - Spasticity/cramps: baclofen, tizanidine, mexiletine (cramps). - Pseudobulbar affect: dextromethorphan/quinidine (Nuedexta). - Rehabilitation: physical (MAXO:0000011), occupational, and speech therapy / AAC communication devices; mobility aids. - Palliative & advance-care planning: hospice, symptom control, respect for ventilation/withdrawal decisions.

Treatment outcomes. Approved drugs yield modest slowing (months), not reversal; combination riluzole + edaravone + supportive care is common. Adverse events: riluzole — transaminitis, asthenia, nausea; edaravone — gait disturbance, bruising, hypersensitivity; tofersen — CSF pleocytosis, myelitis/radiculitis (serious neurologic AEs), headache.

13. Prevention

Primary prevention: No proven strategy; modifiable-risk-factor reduction (smoking cessation) is reasonable. No vaccine/immunization (not infectious).
Secondary prevention / early detection: No population screening. In known-mutation families, presymptomatic genetic testing + NfL surveillance enables early/pre-symptomatic intervention trials (ATLAS in SOD1). Cascade testing with genetic counseling.
Tertiary prevention (complication avoidance): early NIV, PEG, aspiration-pneumonia prevention, DVT/pressure-sore prevention, multidisciplinary clinic follow-up — these prevent complications and extend survival.
Genetic counseling & reproductive options: risk assessment for AD/X-linked/recessive/oligogenic inheritance; preimplantation genetic testing (PGT) and prenatal diagnosis available for known familial mutations (NSGC/ACMG frameworks).
Public-health/environmental: in historical Guam ALS-PDC, dietary/environmental change coincided with declining incidence (BMAA hypothesis).

14. Other Species / Natural Disease

Taxonomy of models/natural disease: human (NCBITaxon:9606); models in mouse (NCBITaxon:10090), rat (NCBITaxon:10116), zebrafish (NCBITaxon:7955), Drosophila (NCBITaxon:7227), C. elegans (NCBITaxon:6239), pig, and non-human primate.
Natural / veterinary disease: Canine degenerative myelopathy (DM) is a naturally-occurring SOD1-associated progressive spinal-cord/motor disorder (notably in German Shepherds, Pembroke Welsh Corgis, Boxers), caused by SOD1 c.118G>A (p.E40K) and a second SOD1 variant — a recognized large-animal ortholog model of SOD1-ALS (OMIA entry for degenerative myelopathy/SOD1 in Canis lupus familiaris). Equine motor neuron disease (EMND), linked to vitamin-E deficiency/oxidative stress, is a naturally-occurring LMN disease in horses resembling sporadic ALS. (Both = MODEL_ORGANISM evidence per dismech rules; document breed with VBO where possible.)
Comparative biology / evolutionary conservation: SOD1, TARDBP, FUS, C9orf72 orthologs are deeply conserved; core mechanisms (proteostasis, RNA metabolism, oxidative stress) are conserved from yeast to human, enabling cross-species modeling (Alliance of Genome Resources).
Transmission / zoonosis: none — ALS is not infectious or zoonotic (prion-like propagation is intracellular templating, not transmissible between individuals).

15. Model Organisms

Rodent (mammalian) — dominant models. - SOD1-G93A transgenic mouse — the classic ALS model; recapitulates progressive motor-neuron loss, paralysis, and shortened lifespan (Gurney et al., Science 1994, PMID:8209258). SOD1-G37R, G85R, D90A lines also used. Rat SOD1-G93A/H46R models for larger-CNS studies (intrathecal dosing, CSF sampling). - TDP-43 models (TARDBP overexpression/knock-in, e.g., Q331K, M337V) — reproduce TDP-43 pathology but overexpression toxicity confounds interpretation. - FUS transgenic/knock-in models — cytoplasmic FUS pathology, motor deficits. - C9orf72 models — BAC-transgenic mice carrying the human expansion (RNA foci + DPRs; variable motor phenotype across labs), AAV-(G4C2)n models, and C9orf72-knockout mice (immune/autophagy phenotype, models haploinsufficiency arm).

Genetic-model types available. Knockout, knock-in, transgenic (BAC), conditional (cell-type-specific to dissect neuron vs astrocyte vs microglia contributions), and humanized lines (MGI/IMPC/IMSR resources).

Non-mammalian & cellular. - Zebrafish (sod1, tardbp, fus, c9orf72 morphants/mutants) — rapid axonal/NMJ phenotyping. - Drosophila and C. elegans — DPR-toxicity and modifier screens (large-scale genetic screens defined nucleocytoplasmic-transport and RNA-metabolism modifiers). - iPSC-derived motor neurons from patient fibroblasts — the leading human in vitro platform (TDP-43 mislocalization, hyperexcitability, survival assays); iPSC-derived astrocytes/microglia and organoids/assembloids for non-cell-autonomous and NMJ modeling. Immortalized lines (NSC-34) for biochemistry.

Phenotype recapitulation & limitations. SOD1 mice reproduce the motor phenotype well but SOD1 accounts for a minority of human ALS and lacks TDP-43 pathology; C9orf72 mouse motor phenotypes are inconsistent between labs (a documented HUMAN_MODEL_MISMATCH: robust molecular pathology without reliable neurodegeneration/paralysis). No single model captures the full sporadic-ALS, TDP-43-centric human disease — a key knowledge gap and a driver of the shift toward patient iPSC systems. (Model databases: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, Cellosaurus.)

Consolidated Ontology-Term Suggestions (for KB population)

MONDO: MONDO:0004976 (ALS); MONDO:0007103 (ALS1/SOD1).
HP (phenotypes): HP:0003323, HP:0003202, HP:0002380, HP:0003394, HP:0001257, HP:0001347, HP:0001260, HP:0002015, HP:0002307, HP:0002878/HP:0002093, HP:0002094, HP:0001824, HP:0000749, HP:0002145, HP:0100543.
GO (processes/CC): GO:0008380, GO:0006406, GO:0010494, GO:0006913, GO:0006914, GO:0043161, GO:0006979, GO:0004784, GO:0051966, GO:0150076, GO:0043065; components GO:0005737, GO:0031594, GO:0005643.
CL (cells): CL:0000100, CL:0011001, CL:0000598, CL:0000127, CL:0000129, CL:0000188.
UBERON (anatomy): UBERON:0001384, UBERON:0002026, UBERON:0002718, UBERON:0002240, UBERON:0001103, UBERON:0001134.
CHEBI (chemicals): CHEBI:8863 (riluzole), CHEBI:31530 (edaravone), CHEBI:14321 (glutamate), CHEBI:29108 (calcium), CHEBI:18421 (superoxide), CHEBI:16240 (hydrogen peroxide).
HGNC (genes): hgnc:11179 (SOD1), hgnc:28337 (C9orf72), hgnc:11571 (TARDBP), hgnc:4010 (FUS), hgnc:11584 (TBK1), hgnc:6323 (KIF5A). (Verify all with OAK — lowercase hgnc: per repo convention.)
MAXO (treatments): pharmacotherapy (riluzole/edaravone/tofersen), mechanical/non-invasive ventilation, gastrostomy, physical therapy (MAXO:0000011), dietary intervention (MAXO:0000088), supportive/palliative care (MAXO:0000950).

Key Landmark Citations (verified real; snippets to be re-fetched before KB commit)

PMID	Citation	Use
8446170	Rosen et al., Nature 1993 — SOD1 mutations in fALS	First ALS gene
8302340	Bensimon et al., N Engl J Med 1994 — riluzole RCT	Treatment/survival
8209258	Gurney et al., Science 1994 — SOD1-G93A mouse	Model organism
16741123	Boillée et al., Science 2006 — microglia/non-cell-autonomous	Neuroinflammation
16488378	Bourke et al., Lancet Neurol 2006 — NIV RCT	Respiratory management
17023659	Neumann et al., Science 2006 — TDP-43 as inclusion protein	Core pathology
18309045	Sreedharan et al., Science 2008 — TARDBP mutations	Genetics
19251627 / 19251628	Kwiatkowski / Vance et al., Science 2009 — FUS	Genetics
20740007	Elden et al., Nature 2010 — ATXN2	Risk/modifier gene
21944778 / 21944779	DeJesus-Hernandez / Renton et al., Neuron 2011 — C9orf72	Most common gene
21857683	Deng et al., Nature 2011 — UBQLN2 (X-linked)	Genetics/proteostasis
23393093 / 23415312	Mori / Ash et al., 2013 — DPR/RAN translation	C9orf72 mechanism
22042175	Roche et al., Brain 2012 — King's staging	Staging
24507800	Al-Chalabi et al., Lancet Neurol 2014 — multistep model	Etiology
26192745	Freischmidt et al., Nat Neurosci 2015 — TBK1	Genetics
27830784	Taylor, Brown, Ravits, Nature 2016 — "Decoding ALS"	Mechanism review
28552366	van Es et al., Lancet 2017 — ALS seminar	Clinical review
28522181	Writing Group, Lancet Neurol 2017 — edaravone RCT	Treatment
28700839	Brown & Al-Chalabi, N Engl J Med 2017 — ALS review	Overview
29566793	Nicolas et al., Neuron 2018 — KIF5A	Genetics
32410883	Shefner et al., Clin Neurophysiol 2020 — Gold Coast criteria	Diagnosis
36170501	Miller et al., N Engl J Med 2022 — VALOR/tofersen	Gene-targeted therapy
36116464	Feldman et al., Lancet 2022 — ALS review	Overview/epidemiology

Sources (web-verified during research)

Curation flags for the KB entry: 1. Model as Complex disease with a monogenic subtype layer (SOD1, C9orf72, TARDBP, FUS, TBK1, KIF5A…) — good candidate for has_subtypes + oligogenic inheritance modeling (C9orf72+ATXN2/TBK1). 2. antisense_oligonucleotide_therapy module conformance (tofersen, RNase-H, SOD1) is a natural fit. 3. Record AMX0035/Relyvrio as withdrawn (2024) — accuracy-critical. 4. Flag C9orf72 mouse HUMAN_MODEL_MISMATCH and sporadic-ALS/TDP-43 model gap as discussions (kind: HUMAN_MODEL_MISMATCH / KNOWLEDGE_GAP). 5. All snippets require just fetch-reference verification before commit; treat HERV-K/BMAA as hypotheses, not established etiology.

Disorder ▸

Disorder

Name: Amyotrophic Lateral Sclerosis
Category: Complex
Existing deep-research providers: falcon
Existing evidence reference count in YAML: 52

Key Pathophysiology Nodes

Motor Neuron Degeneration
TDP-43 Proteinopathy
C9orf72 Repeat Expansion Toxicity
Glutamate Excitotoxicity
Oxidative Stress
Neuroinflammation
Microglial TREM2 Signaling
Axonal Transport Dysfunction
Impaired Autophagy
Genetic Drivers and Therapeutic Translation
Deep research literature mapping

Citation Inventory (for evidence mapping)

DOI:10.1016/s1474-4422(21
DOI:10.1038/s41573-022-00612-2
DOI:10.1093/brain/awae039
DOI:10.3389/fmolb.2025.1608853
DOI:10.3390/cells13110888

Falcon ▸

Pathophysiology description

Edison Scientific Literature 18 citations 2026-01-08T20:58:49.960392

Pathophysiology description ALS is a multisystem neurodegenerative disease characterized by progressive degeneration of upper and lower motor neurons with pervasive disturbances in RNA metabolism, proteostasis, axonal transport, mitochondrial function, excitatory signaling, and neuroimmune homeostasis. A unifying feature is proteinopathy: cytoplasmic aggregation and nuclear depletion of the RNA-binding protein TDP-43 occur in approximately 97% of ALS, disrupting splicing (e.g., STMN2) and RNA handling, with additional, largely mutually exclusive proteinopathies driven by SOD1 or FUS in subsets; C9orf72 repeat expansions add toxic gain-of-function via repeat RNA foci and dipeptide-repeat proteins (DPRs) plus possible haploinsufficiency (G4C2) (first described comprehensively and updated across mechanisms) (https://doi.org/10.1016/S1474-4422(21)00414-2, May 2022; https://doi.org/10.1038/s41573-022-00612-2, Dec 2023) (goutman2022emerginginsightsinto pages 6-8, mead2023amyotrophiclateralsclerosis pages 6-7). Nucleocytoplasmic transport (NCT) defects are a recurring axis linking these proteinopathies to motor neuron vulnerability through nuclear pore complex and Ran-GTPase cycle dysfunction, exacerbated by arginine-rich DPRs (poly-PR/GR) and by FUS/TDP-43 aggregation (https://doi.org/10.1016/S1474-4422(21)00414-2, May 2022) (goutman2022emerginginsightsinto pages 8-9). Excitotoxicity stemming from cortical hyperexcitability, impaired astrocytic glutamate clearance (EAAT2/SLC1A2), and altered receptor composition is increasingly viewed as a convergent pathway (“dying forward” hypothesis), even as clinical trial experience underscores the need to better map the route from hyperexcitability to neuronal death (https://doi.org/10.1093/brain/awae039, Feb 2024) (nguyen2024updatesondisease pages 1-2). Mitochondrial bioenergetic defects, oxidative stress, and mitophagy/autophagy impairment coexist with axonal transport failure and early neuromuscular junction (NMJ) denervation, while glial and peripheral immune responses (microglia, astrocytes, monocytes/NK cells) shape progression (https://doi.org/10.1016/S1474-4422(21)00414-2, May 2022; https://doi.org/10.1038/s41573-022-00612-2, Dec 2023) (goutman2022emerginginsightsinto pages 26-28, mead2023amyotrophiclateralsclerosis pages 6-7).

Key concepts and definitions with current understanding - Proteinopathy and ribostasis: “TDP-43 pathology is characteristic of the majority of ALS cases,” with mislocalization and aggregation that impair RNA splicing, including STMN2, and engage stress granule/LLPS biology; SOD1 and FUS drive alternative proteopathic subtypes (https://doi.org/10.1016/S1474-4422(21)00414-2, 2022) (goutman2022emerginginsightsinto pages 6-8). - C9orf72 repeat expansion: Dual mechanisms—loss of function (haploinsufficiency) and gain of function via repeat RNA and DPRs (poly-PR/GR/GA)—that converge on NCT, heterochromatin, proteostasis, and trigger TDP-43 pathology (https://doi.org/10.1016/S1474-4422(21)00414-2, 2022) (goutman2022emerginginsightsinto pages 8-9). - Nucleocytoplasmic transport (NCT): Nuclear pore, importin/Ran cycle, and nuclear envelope alterations present in human ALS tissue and models; DPRs and FUS/TDP-43 assemblies disrupt nuclear import/export (https://doi.org/10.1016/S1474-4422(21)00414-2, 2022) (goutman2022emerginginsightsinto pages 8-9). - Excitotoxicity: Cortical hyperexcitability and impaired EAAT2-mediated glutamate clearance contribute to glutamate-driven neuronal injury; translational gaps remain between biomarkers/physiology and therapy (https://doi.org/10.1093/brain/awae039, 2024) (nguyen2024updatesondisease pages 1-2). - Axonal transport/NMJ: Trafficking gene hits (KIF5A, DCTN1, PFN1) and early NMJ denervation align with a “dying-back” contribution to weakness (https://doi.org/10.1016/S1474-4422(21)00414-2, 2022; https://doi.org/10.1038/s41573-022-00612-2, 2023) (goutman2022emerginginsightsinto pages 22-26, mead2023amyotrophiclateralsclerosis pages 6-7). - Mitochondrial dysfunction/oxidative stress: Mutations/aggregates compromise mitochondrial dynamics and respiration, elevating ROS and linking to bioenergetic biomarkers (31P-MRS) (https://doi.org/10.1038/s41573-022-00612-2, 2023) (mead2023amyotrophiclateralsclerosis pages 6-7). - Neuroinflammation: Microglial/astrocytic activation states and infiltration of peripheral immune effectors (e.g., NK cells) accompany motor neuron loss and may modulate trajectory (https://doi.org/10.1016/S1474-4422(21)00414-2, 2022) (goutman2022emerginginsightsinto pages 26-28).

Recent developments and latest research (2023–2024 prioritized) - Comprehensive therapeutic translation map (2023): An advanced pipeline targets proteostasis, RNA metabolism, mitochondria, and inflammation; PB-TURSO (phenylbutyrate/taurursodiol) slowed ALSFRS-R decline and improved survival in a phase II study, highlighting mitochondrial/proteostasis targeting (https://doi.org/10.1038/s41573-022-00612-2, Dec 2023) (mead2023amyotrophiclateralsclerosis pages 6-7). - Excitotoxicity reappraisal (2024): Mechanistic synthesis clarifies primary (synaptic) and secondary (intracellular) cascades and emphasizes EAAT2 and cortical network-level hyperexcitability as strategic targets (https://doi.org/10.1093/brain/awae039, Feb 2024) (nguyen2024updatesondisease pages 1-2). - Biomarker integration (2025 review summarizing 2023–2024): Neurofilament light (NfL) and pNfH support diagnosis/prognosis; poly-GP DPRs serve as target-engagement readouts in C9orf72 trials; digital and imaging biomarkers are rising (https://doi.org/10.3389/fmolb.2025.1608853, Jun 2025, cites 2023–2024 primary data) (anjum2025emergingbiomarkersin pages 2-3).

Current applications and real-world implementations - Gene-directed therapy: Tofersen (SOD1 ASO) achieved CSF SOD1 reduction and is used in gene-directed contexts; biomarker (NfL) trajectories help demonstrate pharmacodynamic impact and support presymptomatic trial design (NCT references in 2022–2023 synthesis) (https://doi.org/10.1016/S1474-4422(21)00414-2, 2022; https://doi.org/10.1038/s41573-022-00612-2, 2023) (goutman2022emerginginsightsinto pages 6-8, mead2023amyotrophiclateralsclerosis pages 6-7). - Biomarkers in practice: Blood/CSF NfL and pNfH increasingly aid differential diagnosis and prognosis and are incorporated into trial enrichment and monitoring plans (https://doi.org/10.3389/fmolb.2025.1608853, 2025) (anjum2025emergingbiomarkersin pages 2-3).

Expert opinions and analysis from authoritative sources - “ALS is poised for successful therapeutic translation,” with mechanistic subclassification and biomarker-enabled trials expected to improve translation across heterogeneous subtypes (Nature Reviews Drug Discovery, Dec 2023) (mead2023amyotrophiclateralsclerosis pages 6-7). - “Evidence of increased glutamate and hyperexcitability… provides an empirical support base for the ‘dying forward’ excitotoxicity hypothesis,” yet mapping hyperexcitability to excitotoxicity requires refined experimental paradigms to guide therapy (Brain, Feb 2024) (nguyen2024updatesondisease pages 1-2).

Relevant statistics and data from recent studies - Epidemiology and genetics: Prevalence 4–8 per 100,000; onset 55–60 years; ~10% familial (fALS), ~90% sporadic; C9orf72 expansions are the most common genetic cause in Europe/USA fALS (~40–50%) and present in ~5–10% of sALS; SOD1 mutations ~2% of sALS (Cells, May 2024) (https://doi.org/10.3390/cells13110888) (nguyen2024updatesondisease pages 1-2). - Pathology ubiquity: “TAR DNA-binding protein 43 (TDP-43) inclusions are observed in ~97% of those diagnosed with amyotrophic lateral sclerosis,” underscoring TDP-43 as the dominant proteopathy (Lancet Neurology, May 2022) (goutman2022emerginginsightsinto pages 6-8).

Research Objectives Comprehensive report on the molecular and cellular mechanisms underlying ALS disease progression

1) Core Pathophysiology - Primary pathophysiological mechanisms - Protein aggregation with nuclear depletion of RBPs (TDP-43, FUS) and SOD1/FUS proteinopathy subtypes; TDP-43 proteinopathy dominates and impairs splicing (e.g., STMN2), RNA transport, and stress granule dynamics (LLPS) (https://doi.org/10.1016/S1474-4422(21)00414-2, 2022) (goutman2022emerginginsightsinto pages 6-8). - C9orf72 repeat RNA and DPR toxicity plus haploinsufficiency converge on NCT, chromatin, translation, and proteostasis; DPRs (poly-PR/GR) bind nucleic acids and NCT factors, impairing nuclear function (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 8-9). - NCT breakdown involving nuclear pore components, importins, Ran-GTPase cycle, and nuclear envelope morphology in ALS motor cortex and spinal motor neurons (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 8-9). - Glutamate excitotoxicity via cortical hyperexcitability and astrocytic EAAT2 downregulation, with primary synaptic and secondary intracellular cascades (Brain 2024) (nguyen2024updatesondisease pages 1-2). - Mitochondrial respiratory/bioenergetic dysfunction with oxidative stress; preclinical/clinical mitochondrial-targeting strategies are in development or translation (Nature Rev Drug Discov 2023) (mead2023amyotrophiclateralsclerosis pages 6-7). - Axonal transport failure and early NMJ denervation (dying-back) intersect with cytoskeletal gene defects (KIF5A, DCTN1, PFN1) (Lancet Neurology 2022; Nature Rev Drug Discov 2023) (goutman2022emerginginsightsinto pages 22-26, mead2023amyotrophiclateralsclerosis pages 6-7). - Neuroinflammation with CNS microglial/astrocytic activation and peripheral immune contributions (NK cells, monocytes), including infiltration and altered cytokines (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 26-28).

Dysregulated molecular pathways
RNA metabolism and splicing; stress granule/LLPS persistence; autophagy–lysosome and ubiquitin–proteasome systems (UPS) failure; NCT and nuclear pore dysfunction; glutamatergic transmission and transporter regulation; mitochondrial dynamics/mitophagy; axonal trafficking and cytoskeletal integrity; innate/adaptive immune signaling (Lancet Neurology 2022; Nature Rev Drug Discov 2023) (goutman2022emerginginsightsinto pages 22-26, mead2023amyotrophiclateralsclerosis pages 6-7).
Affected cellular processes
mRNA splicing (e.g., STMN2), RNA transport, ribostasis; protein quality control and degradation; organelle transport; calcium/ROS homeostasis; synaptic transmission; microglial–astrocyte reactivity states and leukocyte trafficking (Lancet Neurology 2022; Brain 2024; Nature Rev Drug Discov 2023) (goutman2022emerginginsightsinto pages 6-8, nguyen2024updatesondisease pages 1-2, mead2023amyotrophiclateralsclerosis pages 6-7).

2) Key Molecular Players - Genes/Proteins (HGNC recommended symbols) - TARDBP (TDP-43): RBP, aggregation/nuclear depletion in ~97% ALS; RNA splicing impairment (STMN2) (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 6-8). - SOD1: misfolding/aggregation, oxidative stress, mitochondrial/axonal transport defects; target of ASO therapy (Nature Rev Drug Discov 2023) (mead2023amyotrophiclateralsclerosis pages 6-7). - FUS: RBP with LLPS/stress granule biology and NCT linkage (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 22-26). - C9orf72: G4C2 repeat expansion driving RNA foci and DPRs (poly-PR/GR/GA) with NCT/chromatin/proteostasis toxicity plus potential haploinsufficiency (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 8-9). - Additional implicated/modifier genes: KIF5A, DCTN1, PFN1 (axonal/cytoskeleton); TBK1, OPTN, VCP, SQSTM1, CCNF, DNAJC7 (autophagy–UPS); NEK1, C21orf2 (DNA repair/axon cilium); TIA1 (RNA granules) (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 29-30, goutman2022emerginginsightsinto pages 22-26).

Chemical Entities / Biomarkers (CHEBI where applicable)
Glutamate (CHEBI:14321): excitatory neurotransmitter driving excitotoxic cascades; elevated CSF reported in subsets (Brain 2024; Cells 2024) (nguyen2024updatesondisease pages 1-2).
Neurofilament light (NfL) and phosphorylated neurofilament heavy (pNfH): fluid biomarkers of axonal injury with diagnostic/prognostic value and utility in trials (Frontiers Mol Biosci 2025) (anjum2025emergingbiomarkersin pages 2-3).
Cell Types (CL)
Motor neurons (upper cortical and lower spinal/brainstem) are primary degenerating cells; astrocytes and microglia show reactive phenotypes; peripheral NK cells/monocytes may contribute (Lancet Neurology 2022; Brain 2024) (goutman2022emerginginsightsinto pages 26-28, nguyen2024updatesondisease pages 1-2).
Anatomical Locations (UBERON)
Motor cortex and corticospinal tract; spinal anterior horn; brainstem motor nuclei; neuromuscular junctions and skeletal muscle (Lancet Neurology 2022; Nature Rev Drug Discov 2023) (mead2023amyotrophiclateralsclerosis pages 6-7, goutman2022emerginginsightsinto pages 22-26).

3) Biological Processes (for GO annotation) - RNA splicing and mRNA processing (GO:0008380), RNA transport (GO:0051028) perturbed by TDP-43/FUS (goutman2022emerginginsightsinto pages 6-8, goutman2022emerginginsightsinto pages 22-26). - Protein quality control via UPS (GO:0030433) and autophagy–lysosome pathways (GO:0006914) impaired (goutman2022emerginginsightsinto pages 22-26, mead2023amyotrophiclateralsclerosis pages 6-7). - Nucleocytoplasmic transport (GO:0006913/GO:0051169) disrupted (goutman2022emerginginsightsinto pages 8-9). - Glutamatergic synaptic transmission (GO:0098978) and glutamate uptake (EAAT2/SLC1A2) (GO:0015813) dysregulated (nguyen2024updatesondisease pages 1-2). - Mitochondrial organization (GO:0007005), oxidative phosphorylation (GO:0006119), and mitophagy (GO:0000422) impaired (mead2023amyotrophiclateralsclerosis pages 6-7). - Axonal transport (GO:0098930) and cytoskeletal organization (GO:0007010) defective (goutman2022emerginginsightsinto pages 22-26). - Microglial activation (GO:0001774) and astrocyte activation (GO:0061893) with peripheral immune cell infiltration (goutman2022emerginginsightsinto pages 26-28).

4) Cellular Components - Stress granules (GO:0010494), cytoplasmic aggregates/inclusions; nuclear pore complex (GO:0005643) and nuclear envelope; mitochondria (GO:0005739), ER (GO:0005783); synapse (GO:0045202) and NMJ (GO:0031594); axon (GO:0030424) (goutman2022emerginginsightsinto pages 8-9, mead2023amyotrophiclateralsclerosis pages 6-7, goutman2022emerginginsightsinto pages 22-26).

5) Disease Progression - Proposed sequence (population- and model-informed): Molecular triggers (genetic variants/environmental exposures) initiate ribostasis/proteostasis stress and NCT dysfunction; cortical hyperexcitability and impaired glutamate uptake promote “dying forward” stress on spinal motor neurons; in parallel, axonal transport failure and early NMJ denervation contribute “dying back” pathology; mitochondrial failure and oxidative stress amplify injury; reactive microglia/astrocytes and infiltrating immune cells modulate progression; clinical manifestations spread regionally following neuroanatomical connectivity (Lancet Neurology 2022; Brain 2024; Nature Rev Drug Discov 2023) (goutman2022emerginginsightsinto pages 22-26, nguyen2024updatesondisease pages 1-2, mead2023amyotrophiclateralsclerosis pages 6-7). - Stages: Presymptomatic biomarker phase (e.g., rising NfL) → focal onset (spinal/bulbar) → regional spread with mixed UMN/LMN signs → respiratory failure/end-stage (Nature Rev Drug Discov 2023; Cells 2024) (mead2023amyotrophiclateralsclerosis pages 6-7, nguyen2024updatesondisease pages 1-2).

6) Phenotypic Manifestations (HPO) - Muscle weakness (HP:0001324), fasciculations (HP:0003403), spasticity (HP:0001257), dysarthria (HP:0001260), dysphagia (HP:0002015), respiratory insufficiency (HP:0002093), frontotemporal cognitive/behavioral changes in a subset (HP:0002145) (Cells 2024) (nguyen2024updatesondisease pages 1-2). - Biological correlates: Elevated NfL/pNfH predict faster progression; CSF glutamate elevations in a subset correlate with spinal features; presence of TDP-43 inclusions is near-universal in non-SOD1/FUS subtypes (Brain 2024; Lancet Neurology 2022; Frontiers Mol Biosci 2025) (nguyen2024updatesondisease pages 1-2, goutman2022emerginginsightsinto pages 6-8, anjum2025emergingbiomarkersin pages 2-3).

Gene/Protein annotations with ontology terms (examples) - TARDBP (HGNC:11577): RNA splicing/transport (GO:0008380/GO:0051028); stress granule dynamics (GO:0010494); nucleus/cytoplasm (GO:0005634/GO:0005737). Evidence: TDP-43 pathology and splicing defects (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 6-8). - SOD1 (HGNC:11179): Response to oxidative stress (GO:0006979), mitochondrial organization (GO:0007005); cytosol/mitochondrion (GO:0005829/GO:0005739). Evidence: oxidative stress/mitochondrial dysfunction (Nature Rev Drug Discov 2023) (mead2023amyotrophiclateralsclerosis pages 6-7). - FUS (HGNC:4010): RNA binding/LLPS; nucleus/cytoplasm; NCT. Evidence: RBP with LLPS/NCT involvement (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 22-26). - C9orf72 (HGNC:28396): Autophagy/endolysosomal trafficking (GO:0006914), nucleocytoplasmic transport perturbation; cytosol/nucleus. Evidence: repeat RNA/DPR toxicity and NCT effects (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 8-9). - TBK1 (HGNC:11584), OPTN (HGNC:17195), VCP (HGNC:12666), SQSTM1 (HGNC:11276): Autophagy/UPS; cytoplasm/lysosome. Evidence: autophagy–proteostasis gene set in ALS (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 29-30). - KIF5A (HGNC:8939), DCTN1 (HGNC:2711), PFN1 (HGNC:8897): Axonal transport/cytoskeleton (GO:0098930/GO:0007010); axon. Evidence: trafficking/cytoskeletal defects in ALS (Lancet Neurology 2022) (goutman2022emerginginsightsinto pages 22-26).

Cell type involvement (CL terms) - Upper motor neurons (CL:0002603) and lower motor neurons (CL:1001608) degenerate; astrocytes (CL:0000127) show reactive states including EAAT2 dysregulation; microglia (CL:0000129) activate and interact with infiltrating immune cells; peripheral NK cells (CL:0000623) exhibit altered signatures (Lancet Neurology 2022; Brain 2024) (goutman2022emerginginsightsinto pages 26-28, nguyen2024updatesondisease pages 1-2).

Anatomical locations (UBERON terms) - Primary motor cortex (UBERON:0001384), corticospinal tract (UBERON:0005346), spinal cord anterior horn (UBERON:0002240), brainstem motor nuclei (UBERON:0019267), neuromuscular junction (UBERON:0001981), skeletal muscle (UBERON:0001134) (Lancet Neurology 2022; Nature Rev Drug Discov 2023) (goutman2022emerginginsightsinto pages 22-26, mead2023amyotrophiclateralsclerosis pages 6-7).

Chemical entities (CHEBI terms) - Glutamate (CHEBI:14321) (excitotoxic mediator) (Brain 2024) (nguyen2024updatesondisease pages 1-2). - Neurofilament light (not in CHEBI; protein biomarker) and pNfH (protein biomarker) (Frontiers Mol Biosci 2025) (anjum2025emergingbiomarkersin pages 2-3).

Evidence items with PMIDs/DOIs/URLs and dates - Goutman SA et al. Emerging insights into the complex genetics and pathophysiology of ALS. Lancet Neurol. May 2022. DOI: 10.1016/S1474-4422(21)00414-2; URL: https://doi.org/10.1016/S1474-4422(21)00414-2 (goutman2022emerginginsightsinto pages 6-8, goutman2022emerginginsightsinto pages 8-9, goutman2022emerginginsightsinto pages 29-30, goutman2022emerginginsightsinto pages 26-28, goutman2022emerginginsightsinto pages 22-26). - Mead RJ et al. ALS: poised for successful therapeutic translation. Nat Rev Drug Discov. Dec 2023. DOI: 10.1038/s41573-022-00612-2; URL: https://doi.org/10.1038/s41573-022-00612-2 (mead2023amyotrophiclateralsclerosis pages 6-7). - Odierna GL et al. How do we get from hyperexcitability to excitotoxicity in ALS? Brain. Feb 2024. DOI: 10.1093/brain/awae039; URL: https://doi.org/10.1093/brain/awae039 (nguyen2024updatesondisease pages 1-2). - Anjum F et al. Emerging biomarkers in ALS. Frontiers Mol Biosci. Jun 2025 (synthesizes 2023–2024 studies). DOI: 10.3389/fmolb.2025.1608853; URL: https://doi.org/10.3389/fmolb.2025.1608853 (anjum2025emergingbiomarkersin pages 2-3).

Direct quotes - “TAR DNA-binding protein 43 (TDP-43) inclusions are observed in ~97% of those diagnosed with amyotrophic lateral sclerosis” (Lancet Neurology, 2022) (goutman2022emerginginsightsinto pages 6-8). - “Evidence of increased glutamate and hyperexcitability… provides an empirical support base for the ‘dying forward’ excitotoxicity hypothesis” (Brain, 2024) (nguyen2024updatesondisease pages 1-2). - “ALS is… poised for successful therapeutic translation” with mechanistic subclassification and biomarkers enabling improved trial design (Nat Rev Drug Discov, 2023) (mead2023amyotrophiclateralsclerosis pages 6-7).

Notes and limitations - Where 2025 reviews are cited, we relied on their synthesis of 2023–2024 primary data for biomarker/application context; mechanistic anchors derive from 2022–2024 high-quality reviews and analyses. Future additions should incorporate single-cell atlases and proteomic maps as they are qualified and publicly accessible.

References

(goutman2022emerginginsightsinto pages 6-8): Stephen A Goutman, Orla Hardiman, Ammar Al-Chalabi, Adriano Chió, Masha G Savelieff, Matthew C Kiernan, and Eva L Feldman. Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis. The Lancet Neurology, 21:465-479, May 2022. URL: https://doi.org/10.1016/s1474-4422(21)00414-2, doi:10.1016/s1474-4422(21)00414-2. This article has 398 citations and is from a highest quality peer-reviewed journal.
(mead2023amyotrophiclateralsclerosis pages 6-7): Richard J. Mead, Ning Shan, H. Joseph Reiser, Fiona Marshall, and Pamela J. Shaw. Amyotrophic lateral sclerosis: a neurodegenerative disorder poised for successful therapeutic translation. Nature Reviews. Drug Discovery, 22:185-212, Dec 2023. URL: https://doi.org/10.1038/s41573-022-00612-2, doi:10.1038/s41573-022-00612-2. This article has 493 citations.
(goutman2022emerginginsightsinto pages 8-9): Stephen A Goutman, Orla Hardiman, Ammar Al-Chalabi, Adriano Chió, Masha G Savelieff, Matthew C Kiernan, and Eva L Feldman. Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis. The Lancet Neurology, 21:465-479, May 2022. URL: https://doi.org/10.1016/s1474-4422(21)00414-2, doi:10.1016/s1474-4422(21)00414-2. This article has 398 citations and is from a highest quality peer-reviewed journal.
(nguyen2024updatesondisease pages 1-2): Lien Nguyen. Updates on disease mechanisms and therapeutics for amyotrophic lateral sclerosis. Cells, 13:888, May 2024. URL: https://doi.org/10.3390/cells13110888, doi:10.3390/cells13110888. This article has 20 citations and is from a poor quality or predatory journal.
(goutman2022emerginginsightsinto pages 26-28): Stephen A Goutman, Orla Hardiman, Ammar Al-Chalabi, Adriano Chió, Masha G Savelieff, Matthew C Kiernan, and Eva L Feldman. Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis. The Lancet Neurology, 21:465-479, May 2022. URL: https://doi.org/10.1016/s1474-4422(21)00414-2, doi:10.1016/s1474-4422(21)00414-2. This article has 398 citations and is from a highest quality peer-reviewed journal.
(goutman2022emerginginsightsinto pages 22-26): Stephen A Goutman, Orla Hardiman, Ammar Al-Chalabi, Adriano Chió, Masha G Savelieff, Matthew C Kiernan, and Eva L Feldman. Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis. The Lancet Neurology, 21:465-479, May 2022. URL: https://doi.org/10.1016/s1474-4422(21)00414-2, doi:10.1016/s1474-4422(21)00414-2. This article has 398 citations and is from a highest quality peer-reviewed journal.
(anjum2025emergingbiomarkersin pages 2-3): Farah Anjum, Maha Bakhuraysah, Abdulaziz Alsharif, Taj Mohammad, Anas Shamsi, and Md. Imtaiyaz Hassan. Emerging biomarkers in amyotrophic lateral sclerosis: from pathogenesis to clinical applications. Frontiers in Molecular Biosciences, Jun 2025. URL: https://doi.org/10.3389/fmolb.2025.1608853, doi:10.3389/fmolb.2025.1608853. This article has 1 citations and is from a poor quality or predatory journal.
(goutman2022emerginginsightsinto pages 29-30): Stephen A Goutman, Orla Hardiman, Ammar Al-Chalabi, Adriano Chió, Masha G Savelieff, Matthew C Kiernan, and Eva L Feldman. Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis. The Lancet Neurology, 21:465-479, May 2022. URL: https://doi.org/10.1016/s1474-4422(21)00414-2, doi:10.1016/s1474-4422(21)00414-2. This article has 398 citations and is from a highest quality peer-reviewed journal.

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