Adult-Onset Proximal Spinal Muscular Atrophy, Autosomal Dominant

Mendelian MONDO:0008453 Pathograph 28 Show in embeddings browser hereditary disease Motor Neuron Disease Neuromuscular Disease

Adult-onset proximal spinal muscular atrophy, autosomal dominant — the Finkel type of late-onset SMA — is a dominantly inherited lower motor neuron disease caused by heterozygous variation in VAPB, in nearly every reported family the recurrent p.Pro56Ser allele. Onset is in mid-adult life with proximal, lumbar-predominant weakness and neurogenic muscle atrophy that ascends slowly over decades. VAPB is an integral endoplasmic reticulum adaptor that builds membrane contact sites between the ER and essentially every other organelle; p.Pro56Ser sits in its major sperm protein (MSP) domain and renders the protein unstable, aggregation-prone and non-functional. The entity's defining curatorial problem is that the same allele does not produce one disease. The 2004 discovery paper found p.Pro56Ser in seven kindreds presenting variously as late-onset SMA, as atypical slowly progressive ALS (ALS8), and as typical rapidly progressive ALS; a 2026 series of 78 molecularly confirmed patients found that 42% presented as pure lower motor neuron progressive muscular atrophy while a majority eventually showed subtle upper motor neuron signs. This entry is scoped to the pure lower motor neuron, proximal-onset end of that spectrum, and records the continuity with ALS8 explicitly rather than pretending to a clean boundary.

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2
Mappings
1
Inheritance
10
Pathophys.
14
Phenotypes
2
Hypotheses
3
Gaps
28
Pathograph
1
Genes
3
Medical Actions
3
Differentials
4
Models
24
References
1
Deep Research
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Classifications

Harrison's Part
NEUROLOGIC GENETICS ENVIRONMENT DISEASE
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Mappings

ICD-10-CM
ICD10CM:G12.1 Other inherited spinal muscular atrophy
skos:broadMatch ORPHA:209335
semapv:ManualMappingCuration
ICD-11 Foundation
icd11f:353473981 Autosomal dominant proximal spinal muscular atrophy
skos:broadMatch
semapv:ManualMappingCuration
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Inheritance

1
Autosomal dominant inheritance HP:0000006
A single heterozygous VAPB p.Pro56Ser allele is sufficient. The disorder was mapped in a large Brazilian kindred and the same variant then found in six further kindreds; haplotype analysis across eight families of both Portuguese-Brazilian and African-Brazilian ancestry places the origin in a single founding event, so most of the world's reported patients share one ancestral chromosome rather than representing independent mutational events.
Autosomal dominant inheritance
Show evidence (2 references)
PMID:15372378 SUPPORT Human Clinical
"Subsequently, the same mutation was identified in patients from six additional kindreds but with different clinical courses, such as ALS8, late-onset SMA, and typical severe ALS with rapid progression."
Documents segregation of a single heterozygous allele across seven kindreds, including the late-onset SMA presentation this entry curates.
PMID:16187141 SUPPORT Human Clinical
"Haplotype analysis shows a common founder for all families regardless of ancestry, with a founding event 23 generations ago (95% CI 13-39), consistent with the Portuguese colonization of Brazil."
Establishes the founder origin, which is why allele counts across families cannot be treated as independent observations.
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Mechanistic Hypotheses

2
Dominant-negative sequestration of wild-type VAP
dominant_negative_aggregation CANONICAL
Evidence balance 1 support
The historically dominant reading: mutant VAPB misfolds, forms ER-derived aggregates, and recruits the wild-type VAPA and VAPB products of the normal alleles into those aggregates, so that a heterozygote loses far more VAP function than the 50% a null allele would cost. This explains dominance without invoking a novel toxic activity, and it is directly demonstrated — but in overexpression systems.
Show evidence (1 reference)
PMID:17804640 SUPPORT In Vitro
"Our data support a model in which reduced levels of VAP family proteins result in decreased ER anchoring of lipid-binding proteins and cause motor neuron degeneration."
States the sequestration model in the authors' own terms.
Haploinsufficiency of the wild-type allele
vapb_haploinsufficiency EMERGING
Evidence balance 2 support
The competing reading: at physiological expression a single mutant allele produces too little protein to sequester anything, aggregates are not seen in patient-derived cells, and what actually matters is that the wild-type allele alone cannot supply enough VAPB. On this account the disorder is a haploinsufficiency and the aggregates seen in overexpression systems are an artefact of dose. The two hypotheses are not mutually exclusive — both converge on the same central_effector node — but they imply opposite therapeutic strategies (clear the aggregate versus raise wild-type VAPB).
Show evidence (2 references)
PMID:34440634 SUPPORT Other
"Instead, loss-of-function of the single wild-type allele is required for pathological effects, and VAPB haploinsufficiency may be the main driver of the disease."
States the haploinsufficiency hypothesis explicitly.
PMID:23446633 SUPPORT Model Organism
"Thus, Vapb loss of function weakens the motor system of vertebrate animal models but is on its own unable to lead to a complete ALS phenotype."
Supports a loss-of-function contribution while showing it is not sufficient on its own — which is why this hypothesis is EMERGING rather than superseding the dominant-negative account.
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Discussions and Knowledge Gaps

3
Why does a single founder allele, VAPB p.Pro56Ser, produce late-onset Finkel SMA in some carriers, slowly progressive atypical ALS in others, and rapidly progressive typical ALS in a few?
KNOWLEDGE GAP OPEN vapb_p56s_one_allele_many_phenotypes
Attached to
pathophysiology#VAPB p.Pro56Ser MSP-Domain Variant pathophysiology#Lower Motor Neuron Degeneration
This is the central unresolved question for this entry, and it is unusually well posed because the founder effect removes allelic heterogeneity as an explanation: nearly all reported patients carry the same ancestral chromosome. The 2004 discovery paper already reported the three courses across seven kindreds, and the 2026 series of 78 patients quantified the split — 42% presenting as pure progressive muscular atrophy, of whom 30% later developed upper motor neuron signs. Whatever separates them is therefore modifier, environmental or stochastic, and none has been identified. Practically, this determines whether MONDO:0008453 names a disease or a presentation.
Proposed experiments
Genome-wide modifier scan within the founder pedigree
exp_vapb_modifier_scan_within_founder_pedigree
Because carriers share one ancestral haplotype, a within-pedigree association of genome-wide genotype against presentation category (pure LMN versus UMN-positive) and age at onset isolates modifiers with the causal allele held constant — a design most Mendelian disorders cannot support.
Isogenic corticospinal versus spinal motor neuron comparison
exp_vapb_isogenic_motor_neuron_subtype_panel
Introduce p.Pro56Ser into isogenic iPSC lines differentiated separately to corticospinal-like and spinal motor neurons, and compare ER stress, contact-site integrity and survival, testing whether the corticospinal selectivity seen in the transgenic mouse is a property of the neuron subtype or of the transgene.
Show evidence (3 references)
PMID:42166520 SUPPORT Human Clinical
"At admission, 51% had spinal-onset ALS, 42% progressive muscular atrophy (PMA) and 6% flail leg; 30% of patients with PMA subsequently developed UMN signs."
Quantifies the phenotypic split within one allele and the partial conversion between categories over time.
ORPHA:209335 SUPPORT Other
"A rare, genetic, motor neuron disease characterized by adulthood-onset of slowly progressive, proximal muscular weakness with fasciculations, amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or pyramidal involvement."
Supplies the other half of the problem. Orphanet keeps this entity distinct from ALS8 by defining it as free of bulbar and pyramidal involvement, but the allele that causes it produces both in most carriers. The gap between the reference nosology and the molecular cohort is what makes it unclear whether MONDO:0008453 names a disease or a presentation.
PMID:34133501 SUPPORT Other
"Over the past 68 years, the Finkel type late-onset adult autosomal dominant spinal muscular atrophy (SMA) that is allelic with amyotrophic lateral sclerosis-8 (ALS8) gained a genotype-phenotype correlation among the motor neuron diseases through the work of groups led by Zatz and Marques Jr."
States the allelism directly: Finkel-type SMA and ALS8 are the same locus, which is the premise of this discussion. The open question is not whether the two labels share an allele but why the shared allele produces both. Tagged OTHER because it is a historical review, not a study contributing observations.
Do the ER-derived VAPB aggregates that dominate the mechanistic literature actually form in human motor neurons carrying one p.Pro56Ser allele, or are they an artefact of overexpression?
HUMAN MODEL MISMATCH OPEN vapb_aggregates_absent_at_physiological_expression
Attached to
pathophysiology#ER-Derived Aggregation of Misfolded VAPB
The aggregation-and-sequestration model was built almost entirely in overexpression systems, where mutant VAPB reliably forms tubular ER clusters and drags in wild-type VAP. Three lines of evidence complicate transferring that to patients. Patient-derived iPSC motor neurons show reduced VAPB but no identifiable cytoplasmic aggregates. In transgenic mice the inclusions do not correlate with degeneration, disappear after axotomy, and behave as a reversible ERAD-linked quality-control compartment — possibly protective. Against that, physiological-level knock-in mice do form motor-neuron inclusions, so dose alone does not explain the discrepancy. The mismatch is not academic: it decides whether a therapy should clear aggregates or restore wild-type VAPB, and the two hypotheses in mechanistic_hypotheses point in opposite directions.
Proposed experiments
Aggregate detection in ALS8 patient spinal cord
exp_vapb_aggregate_detection_in_patient_tissue
Examine post-mortem anterior horn tissue from p.Pro56Ser patients for ER-derived VAPB inclusions and for wild-type VAPA/VAPB redistribution, against age-matched controls. This is the observation the whole dominant-negative model rests on and it has not been reported in human motor neurons.
Show evidence (2 references)
PMID:21685205 SUPPORT In Vitro
"Our results suggest that optimal levels of VAPB may play a central role in the pathogenesis of ALS8, in agreement with the observed reduction of VAPB in sporadic ALS."
The patient-cell result reframing the mechanism around VAPB levels rather than aggregates.
PMID:24252306 SUPPORT Model Organism
"The presence of these inclusions does not correlate with signs of axonal and neuronal degeneration, and axotomy leads to their gradual disappearance, indicating that they represent reversible structures."
Uncouples inclusion burden from degeneration in the model where the inclusions are most conspicuous.
Is there any disease-modifying treatment for VAPB-related SMA, and does the SMN-directed therapeutic success in 5q SMA transfer?
KNOWLEDGE GAP OPEN vapb_no_disease_modifying_therapy
Attached to
pathophysiology#Loss of Functional VAPB at ER Membrane Contact Sites
Every treatment curated in this entry is supportive: rehabilitation, mobility aids, noninvasive ventilation, genetic counselling. None of it is disease-modifying, and nothing in `treatments` should be read as implying otherwise — the `target_mechanisms` links land on the downstream manifestations (`Respiratory Insufficiency`, `Loss of Ambulation`) and nowhere on the VAPB chain that produces them. Nutritional and swallowing support belong in the same category but are not curated for want of a disorder-specific citation. The specific hazard worth naming is the shared "spinal muscular atrophy" label: nusinersen, risdiplam and onasemnogene abeparvovec raise SMN protein and are approved for SMN1-related 5q SMA. VAPB disease is non-5q and has normal SMN; those agents have no mechanistic route to it and must not be curated here as treatments. The 21.9-year median survival and the 7-year and 10-year milestones to wheelchair and ventilation are, at present, the substance of what can be offered: anticipatory management on a predictable timeline.
Proposed experiments
Test wild-type VAPB restoration in a physiological model
exp_vapb_wildtype_restoration_preclinical
If haploinsufficiency drives the disease, raising wild-type VAPB should rescue it. Test AAV-delivered or allele-selective upregulation of wild-type VAPB in the P56S knock-in mouse with motor behaviour, neuromuscular junction innervation and ER stress markers as endpoints — a design that also discriminates between this entry's two mechanistic hypotheses, since restoration should fail if the aggregate is the toxic species.
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Pathophysiology

10
VAPB p.Pro56Ser MSP-Domain Variant
A heterozygous germline missense change substitutes serine for a conserved proline at residue 56 of VAPB, within the N-terminal major sperm protein (MSP) homology domain — the surface through which VAPB binds FFAT-motif partners and so recruits lipid-transfer and other proteins to the cytosolic face of the endoplasmic reticulum. Essentially every reported family carries this one allele, inherited from a common founder.
VAPB hgnc:12649 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves VAPB (hgnc:12649). hgnc:12649 is a gene from the HUGO Gene Nomenclature Committee.
Genetic context variant_origin: GERMLINE zygosity: HETEROZYGOUS
Heterozygous germline missense variant in the MSP domain. The functional impact category is deliberately left unset: whether the dominant action is a toxic gain of function through aggregation and sequestration of the wild-type protein, or loss of function of the remaining wild-type allele, is the unresolved question recorded in this entry's mechanistic_hypotheses.
Downstream
ER-Derived Aggregation of Misfolded VAPB
Loss of Functional VAPB at ER Membrane Contact Sites
Show evidence (2 references)
PMID:15372378 SUPPORT Human Clinical
"Here, we report the finding of a novel missense mutation in the vesicle-associated membrane protein/synaptobrevin-associated membrane protein B (VAPB) gene in patients from this family."
The original identification of the causal VAPB variant.
PMID:17804640 SUPPORT In Vitro
"A genetic mutation (P56S) in the conserved major sperm protein homology domain of VAPB has been linked to motor-neuron degeneration in affected amyotrophic lateral sclerosis (ALS) patients."
Locates the variant in the conserved MSP homology domain, which is what makes the FFAT-binding surface the affected function.
ER-Derived Aggregation of Misfolded VAPB
Mutant VAPB misfolds and self-associates into immobile, tubular ER-derived inclusions in motor neurons, dragging endogenous wild-type VAPA and VAPB into the same aggregates. The inclusions are not inert: they are decorated with ER-associated degradation machinery (p97/VCP, Derlin-1, BAP31) and behave as a quality-control compartment formed when misfolded VAPB exceeds ERAD capacity. Their pathogenic weight is contested — see the HUMAN_MODEL_MISMATCH discussion below, since patient-derived motor neurons expressing the allele at physiological level do not show them.
motor neuron CL:0000100 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves motor neuron (CL:0000100). CL:0000100 is a cell type from the Cell Ontology.
protein folding GO:0006457 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal protein folding (GO:0006457). GO:0006457 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Animal models
Vapb P56S knock-in mouse Mouse recapitulates Cytoplasmic inclusions containing P56S VAPB and ubiquitinated protein form selectively in motor neurons at physiological expression level — the counter-observation to the claim that aggregates are purely an overexpression artefact.
Downstream
Loss of Functional VAPB at ER Membrane Contact Sites
ER Stress and Unfolded Protein Response Activation
Show evidence (3 references)
PMID:17804640 SUPPORT In Vitro
"We report that in the CNS, VAPB is abundant in motor neurons and that the P56S substitution causes aggregation of mutant VAPB in immobile tubular ER clusters, perturbs FFAT-motif binding, and traps endogenous VAP in mutant aggregates."
Documents both the aggregation itself and the sequestration of wild-type VAP that underlies the dominant-negative reading of the mechanism.
PMID:24252306 SUPPORT Model Organism
"The data indicate that the VAPB-P56S inclusions represent a novel reversible ER quality control compartment that is formed when the amount of mutant VAPB exceeds the capacity of the ERAD pathway and that isolates misfolded and aggregated VAPB from the rest of the ER."
Characterizes the inclusions as an ERAD-linked quality-control compartment and, importantly, argues they may be protective rather than toxic — PARTIAL because it supports the existence of the node while qualifying its causal role.
PMID:24252306 REFUTE Model Organism
"The presence of these inclusions does not correlate with signs of axonal and neuronal degeneration, and axotomy leads to their gradual disappearance, indicating that they represent reversible structures."
Directly refutes a simple aggregate-causes-degeneration reading in the transgenic mouse: inclusion burden and degeneration are uncoupled.
Loss of Functional VAPB at ER Membrane Contact Sites
However the aggregates are read, the functional consequence converges on too little working VAPB at the ER surface. The mutant protein is unstable and non-functional, and VAPB levels are reduced in patient-derived motor neurons and in ALS spinal cord. Because VAPB is the tether that recruits FFAT-motif partners to the ER, its shortfall degrades a whole family of contact-site functions at once: ER-to-Golgi transport, lipid exchange (with a characteristic rise in phosphatidylinositol-4-phosphate), phosphoinositide and calcium handling, and ER protein quality control.
intermembrane lipid transfer GO:0120009 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased intermembrane lipid transfer (GO:0120009). GO:0120009 is a biological process from the Gene Ontology. ↓ DECREASED endoplasmic reticulum to Golgi vesicle-mediated transport GO:0006888 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased endoplasmic reticulum to Golgi vesicle-mediated transport (GO:0006888). GO:0006888 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
ALS8 patient-derived iPSC motor neurons IPSC DERIVED MODEL VAPB protein is reduced in patient-derived motor neurons relative to non-carrier siblings, at endogenous expression levels.
Downstream
ER Stress and Unfolded Protein Response Activation
Disrupted ER-Mitochondria Contact and Calcium Handling
Impaired Autophagic Flux and RNA-Binding Protein Mislocalization
Autonomic and Unmyelinated Small-Fibre Degeneration VAPB is not motor-neuron-specific, so the same functional shortfall is the presumed cause of the autonomic and small-fibre arm. The intermediates are unknown: nothing in this literature explains why some carriers develop dysautonomia and most do not, and no cell-type-selective mechanism has been proposed.
Show evidence (4 references)
PMID:34440634 SUPPORT Other
"The mutant protein is aggregation-prone, non-functional and unstable, and its expression from a single allele appears to be insufficient to support toxic gain-of-function effects within motor neurons."
States the loss-of-function reading of the allele that this node represents.
PMID:21685205 SUPPORT In Vitro
"We show for the first time that VAPB protein levels are reduced in ALS8-derived motor neurons but, in contrast to over-expression systems, cytoplasmic aggregates could not be identified."
Demonstrates reduced VAPB in patient-derived motor neurons — the direct human-cell evidence for this node, and simultaneously the observation that the aggregate node is not seen at physiological expression.
PMID:18701194 SUPPORT Human Clinical
"Expression of VAPB mRNA and protein was predominantly localised to large motor neurones further supporting the relevance of this finding to disease progression occurring in SALS."
Localizes VAPB expression to large motor neurons in human spinal cord, which is why a VAPB shortfall is cell-type selective. Note this cohort is sporadic ALS, not VAPB-mutant disease.
+ 1 more reference
ER Stress and Unfolded Protein Response Activation
Loss of VAPB-dependent ER quality control and accumulation of misfolded VAPB together activate the ER stress response in motor neurons. In physiological-level knock-in mice this is detectable before any behavioural deficit, which is what makes it a candidate initiating step rather than an end-stage epiphenomenon.
motor neuron CL:0000100 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves motor neuron (CL:0000100). CL:0000100 is a cell type from the Cell Ontology.
response to endoplasmic reticulum stress GO:0034976 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased response to endoplasmic reticulum stress (GO:0034976). GO:0034976 is a biological process from the Gene Ontology. ↑ INCREASED endoplasmic reticulum unfolded protein response GO:0030968 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased endoplasmic reticulum unfolded protein response (GO:0030968). GO:0030968 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
Vapb P56S knock-in mouse Mouse recapitulates ER stress and an autophagic response appear in motor neurons before behavioural deficits, at physiological expression level.
Downstream
Lower Motor Neuron Degeneration
Show evidence (3 references)
PMID:26362257 SUPPORT Model Organism
"The mutant mice demonstrate induction of ER stress and autophagic response in motor neurons before obvious onset of behavioral defects, suggesting that these cellular biological defects might contribute to the initiation of the disease."
Places ER stress upstream of motor deficits at physiological expression levels.
PMID:24271015 SUPPORT Model Organism
"Loss of Vap in flies shows various ERQC associated defects, including protein accumulation, ER expansion, and ER stress."
Establishes that losing VAP function is by itself sufficient to produce ER stress, linking this node to the loss-of-function arm rather than only to aggregation.
PMID:18555774 SUPPORT Model Organism
"The P58S mutation in VAP33 leads to a failure to secrete the MSP domain as well as ubiquitination, accumulation of inclusions in the endoplasmic reticulum, and an unfolded protein response."
The Drosophila orthologue of the human variant produces ER inclusions and a UPR, and additionally fails to secrete the MSP domain — a distinct signalling loss noted here rather than curated as its own chain node because it is invertebrate-only evidence.
Disrupted ER-Mitochondria Contact and Calcium Handling
VAPB is a mitochondria-associated-membrane protein that tethers ER to mitochondria by binding the outer-mitochondrial-membrane protein PTPIP51, and this contact is where calcium released from ER stores is taken up by mitochondria. p.Pro56Ser alters PTPIP51 binding and increases mitochondrial calcium uptake. PROVISIONAL rather than ESTABLISHED because the direct evidence comes from overexpression in cell lines and from yeast and mammalian model systems, not from VAPB-mutant human motor neurons.
mitochondrial calcium ion homeostasis GO:0051560 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal mitochondrial calcium ion homeostasis (GO:0051560). GO:0051560 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Lower Motor Neuron Degeneration
Show evidence (3 references)
PMID:22131369 SUPPORT In Vitro
"Finally, we demonstrate that VAPBP56S has altered binding to PTPIP51 and increases Ca(2+) uptake by mitochondria following release from ER stores."
Direct evidence that the disease allele changes the ER-mitochondria tether and its calcium function.
PMID:24893131 SUPPORT In Vitro
"Here we show that the ER-resident protein VAPB interacts with the mitochondrial protein tyrosine phosphatase-interacting protein-51 (PTPIP51) to regulate ER-mitochondria associations."
Establishes the tethering function that the disease allele perturbs.
PMID:39870504 SUPPORT In Vitro
"Inclusion formation was found to be a developmentally regulated process linked to mitochondrial damage that could be attenuated by reducing ER-mitochondrial contacts."
Reverses the expected direction of the arrow: mitochondrial damage feeds back on inclusion formation through the same contacts, so this node is part of a loop rather than a one-way step.
Impaired Autophagic Flux and RNA-Binding Protein Mislocalization
p.Pro56Ser disturbs both the initiation and the completion of autophagy, with autophagosomes failing to fuse with lysosomes. Aggregates accumulate together with LC3 and p62 and sequester RNA-binding proteins — phosphorylated TDP-43, FUS and Matrin 3 — into persistent stress granules, connecting this disorder to the wider TDP-43 proteinopathy of ALS. The human material is a single ALS8 index patient's muscle biopsy and fibroblasts, which is why the node is PROVISIONAL.
macroautophagy GO:0016236 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased macroautophagy (GO:0016236). GO:0016236 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Lower Motor Neuron Degeneration
Show evidence (2 references)
PMID:33972508 SUPPORT In Vitro
"Detailed investigations of autophagic flux in cell culture models revealed that P56S-VAPB alters both initial and late steps of the autophagy pathway."
Documents the autophagic-flux defect this node represents.
PMID:33972508 SUPPORT In Vitro
"Autophagy and RBP homeostasis are interdependent, as demonstrated by the cytoplasmic mis-localisation of several RBPs including pTDP-43, FUS, Matrin 3 which often sequestered with P56S-VAPB aggregates both in cell culture and in the muscle biopsy of the ALS8 patient."
Links the autophagic defect to RNA-binding-protein mislocalization, including in human patient tissue.
Lower Motor Neuron Degeneration
Anterior-horn and brainstem lower motor neurons become dysfunctional and degenerate. Selectivity is striking and only partly explained: VAPB is abundant in motor neurons, and in the pan-neuronal transgenic mouse the corticospinal population is lost while spinal motor neurons instead show altered C-bouton morphology and impaired rhythmic discharge without frank loss. In humans the clinical picture at the Finkel end of the spectrum is purely lower motor neuron, whereas subtle pyramidal signs appear in a majority of ALS8 patients overall.
motor neuron CL:0000100 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves motor neuron (CL:0000100). CL:0000100 is a cell type from the Cell Ontology.
neuron apoptotic process GO:0051402 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased neuron apoptotic process (GO:0051402). GO:0051402 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
Thy1.2 P56S VAPB transgenic mouse Mouse partially recapitulates Spinal motor neurons show altered C-bouton morphology and impaired spontaneous rhythmic discharge, but do not die; the population that dies is the corticospinal one.
Vapb knockout mouse Mouse fails to recapitulate Complete loss of Vapb produced only mild motor deficits after 18 months and left neuromuscular junctions innervated — no motor neuron disease.
Downstream
Chronic Denervation and Reinnervation of Skeletal Muscle
Reduced Tendon Reflexes Loss of the efferent limb of the monosynaptic stretch reflex. This is why reflexes are reduced or absent rather than brisk, and it is the sign that keeps the bedside picture in the lower motor neuron column.
Bulbar Involvement Extension of the same anterior-horn process to brainstem lower motor neurons. Because it is the bulbar motor nucleus rather than the corticobulbar tract that fails, the resulting deficit is predominantly dysphonia rather than the spastic dysarthria of bulbar-onset ALS.
Show evidence (3 references)
PMID:23771029 SUPPORT Model Organism
"However, only a progressive loss of CSMNs but not SMNs was found in P56S VAPB Tg mice."
Supports motor neuron vulnerability while explicitly qualifying it: in this model the spinal motor neurons that define the human Finkel phenotype did not die.
PMID:23771029 SUPPORT Model Organism
"In SMNs, P56S VAPB promoted a rather selective translocation of VAPB protein onto the postsynaptic site of C-boutons that altered the morphology of C-boutons and impaired the spontaneous rhythmic discharges of SMNs."
Gives the spinal motor neuron a dysfunction phenotype short of death, which is consistent with the very slow human course.
PMID:26362257 SUPPORT Model Organism
"Significantly, the knock-in mice demonstrate accumulation of P56S VAPB protein and ubiquitinated proteins in cytoplasmic inclusions, selectively in motor neurons."
Establishes motor neuron selectivity of the cellular pathology at physiological expression level.
Chronic Denervation and Reinnervation of Skeletal Muscle
Failing motor neurons denervate their muscle fibres; surviving units sprout and reinnervate them, which is why electromyography in these patients shows ongoing denervation together with reinnervation rather than acute denervation alone. This compensation is what buys the disorder its decades-long course, and its eventual exhaustion is what produces clinically apparent weakness.
skeletal muscle fiber CL:0008002 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves skeletal muscle fiber (CL:0008002). CL:0008002 is a cell type from the Cell Ontology.
Downstream
Proximal Neurogenic Weakness and Muscle Atrophy
Fasciculations Spontaneous discharge of unstable, partly denervated motor units — the clinical surface of the denervation-reinnervation process this node describes.
Neurogenic Muscle Atrophy Muscle fibres that lose their motor neuron and are not recaptured by a sprouting neighbour atrophy, giving the grouped-fibre pattern of a neurogenic rather than myopathic process.
Distal Tremor Postural tremor attributed to the enlarged motor units produced by collateral reinnervation, not to a cerebellar or extrapyramidal lesion. Curated as an indirect edge because the intermediate is inferred from general motor-unit physiology rather than measured in these patients.
Show evidence (2 references)
PMID:16967488 SUPPORT Human Clinical
"Electromyography disclosed ongoing denervation and reinnervation."
Direct human electrophysiological evidence for this node.
PMID:32383641 SUPPORT Human Clinical
"Electromyography showed widespread neuropathic damage."
Independent replication of the neurogenic electrodiagnostic pattern in an unrelated p.Pro56Ser family outside Brazil.
Proximal Neurogenic Weakness and Muscle Atrophy
The clinical endpoint: proximal and axial weakness with neurogenic muscle atrophy, beginning in the lumbar region in the great majority of patients and ascending over years. Reflexes are reduced and sensation is preserved, which is what separates this from a sensorimotor neuropathy.
Downstream
Proximal Muscle Weakness The clinical expression of this node: proximal, lumbar-predominant weakness that ascends over years.
Camptocormia Axial extension of the same neurogenic weakness. Failure of the paraspinal extensors produces forward flexion of the trunk, and of the abdominal wall the abdominal protrusion described in the original kindred.
Loss of Ambulation Wheelchair dependence at a median of 7 years from onset is the point at which the accumulating proximal deficit crosses a functional threshold, not a separate mechanism.
Respiratory Insufficiency The same ascending neurogenic weakness reaching the respiratory muscles, which is why noninvasive ventilation follows loss of ambulation on a predictable interval (7 years to wheelchair, 10 to ventilation) and why respiratory failure is the terminal event.
Show evidence (2 references)
PMID:16967488 SUPPORT Human Clinical
"In this family, proximal and axial muscle weakness and atrophy, associated with abdominal protrusion, defined the motor phenotype."
Describes the motor endpoint of the chain in a VAPB p.Pro56Ser kindred.
PMID:42166520 SUPPORT Human Clinical
"Onset was lumbar in 94%, proximally predominant."
Quantifies the proximal, lumbar-onset distribution across 78 molecularly confirmed patients.
Autonomic and Unmyelinated Small-Fibre Degeneration
A parallel, non-motor arm of the same VAPB deficit: peripheral autonomic and other unmyelinated fibres degenerate. Sural nerve biopsy in a p.Pro56Ser family showed loss of nerve fibres with a marked unmyelinated-fibre predominance and collagen pockets on electron microscopy, and the sympathetic skin response was absent. This is curated as a distinct arm rather than as part of lower motor neuron degeneration because the affected fibres are not motor, and as PROVISIONAL because it rests on two families — the original Brazilian kindred and an unrelated Chinese one — rather than on the large molecularly confirmed series, which did not assess autonomic function.
Downstream
Dysautonomia Loss of peripheral autonomic fibres produces the sudomotor, cardiovascular, gastrointestinal and sexual dysfunction recorded as the dysautonomia phenotype.
Show evidence (3 references)
PMID:32383641 SUPPORT Human Clinical
"Sural nerve biopsy revealed loss of nerve fibers, especially unmyelinated fibers."
The direct histological observation this node asserts.
PMID:32383641 SUPPORT Human Clinical
"This report indicates that VAPB-associated ALS may be accompanied by multifocal autonomic nerve damage."
The authors' own conclusion, and the hedge ("may be") that keeps this node at PROVISIONAL confidence.
PMID:16967488 SUPPORT Human Clinical
"Autonomic abnormalities were also present, including choking, chronic intestinal constipation, sexual dysfunction, and sudomotor abnormalities, and on nerve morphology there was involvement of unmyelinated fibers."
Independent replication of unmyelinated-fibre involvement, in the original Brazilian kindred rather than the Chinese family.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Adult-Onset Proximal Spinal Muscular Atrophy, Autosomal Dominant Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

14
Digestive 1
Constipation HP:0002019 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Constipation (HP:0002019), qualified as temporality chronic. HP:0002019 is a phenotype from the Human Phenotype Ontology.
Temporal: CHRONIC
Show evidence (1 reference)
PMID:16967488 SUPPORT Human Clinical
"Autonomic abnormalities were also present, including choking, chronic intestinal constipation, sexual dysfunction, and sudomotor abnormalities, and on nerve morphology there was involvement of unmyelinated fibers."
Names chronic intestinal constipation among the autonomic features.
Musculoskeletal 4
Proximal Muscle Weakness VERY_FREQUENT HP:0003701 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Proximal muscle weakness (HP:0003701), qualified as course progressive; adult onset, mean 44.9y. HP:0003701 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE Onset: ADULT; mean 44.9y
Show evidence (3 references)
PMID:42166520 SUPPORT Human Clinical
"Median age at onset was 44.9 years; 51% were men."
Establishes adult onset with a median in the fifth decade and no sex bias.
PMID:42166520 SUPPORT Human Clinical
"Onset was lumbar in 94%, proximally predominant."
94% of 78 molecularly confirmed patients had lumbar, proximally predominant onset, which maps to VERY_FREQUENT (80-100%).
PMID:16967488 SUPPORT Human Clinical
"In this family, proximal and axial muscle weakness and atrophy, associated with abdominal protrusion, defined the motor phenotype."
Independent family-level description of the proximal and axial distribution.
Neurogenic Muscle Atrophy Skeletal muscle atrophy HP:0003202 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Skeletal muscle atrophy (HP:0003202). HP:0003202 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:16967488 SUPPORT Human Clinical
"In this family, proximal and axial muscle weakness and atrophy, associated with abdominal protrusion, defined the motor phenotype."
Documents atrophy alongside the weakness.
Muscle Cramps Muscle spasm HP:0003394 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Muscle cramps, annotated with Muscle spasm (HP:0003394). HP:0003394 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:209335 SUPPORT Other
"A rare, genetic, motor neuron disease characterized by adulthood-onset of slowly progressive, proximal muscular weakness with fasciculations, amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or pyramidal involvement."
The Orphanet definition of this entity names cramps among its cardinal features. Note that this entry records a REFUTE elsewhere against the same sentence, but that disagreement is confined to the clause excluding pyramidal and bulbar involvement; the cramps clause is not in dispute and is corroborated by the wider ALS8 literature.
Respiratory Insufficiency Respiratory insufficiency due to muscle weakness HP:0002747 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Respiratory insufficiency due to muscle weakness (HP:0002747). HP:0002747 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:16967488 SUPPORT Human Clinical
"Death occurred in 10-15 years due to respiratory insufficiency."
Identifies respiratory failure as the terminal event in this kindred.
PMID:42166520 SUPPORT Human Clinical
"Survival was 21.9 years; times to wheelchair dependence and noninvasive ventilation were 7.0 and 10.0 years, respectively."
Quantifies the ventilation milestone across the largest reported series.
Nervous System 2
Fasciculations HP:0002380 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Fasciculations (HP:0002380). HP:0002380 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32383641 SUPPORT Human Clinical
"The clinical features in all patients were camptocormia, fasciculation, and weakness in all limbs."
Documents fasciculation in every affected member of a p.Pro56Ser family.
Distal Tremor FREQUENT HP:0001337 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tremor (HP:0001337). HP:0001337 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:16967488 SUPPORT Human Clinical
"Tone and tendon reflexes were decreased and a distal tremor was common."
"Common" maps to FREQUENT (30-79%) under the GeneReviews prose-to-enum convention; no numerator was reported.
Other 7
Proximal Lower Limb Onset Weakness VERY_FREQUENT Proximal lower limb muscle weakness HP:0008994 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Proximal lower limb muscle weakness (HP:0008994), qualified as adult onset. HP:0008994 is a phenotype from the Human Phenotype Ontology.
Onset: ADULT
Show evidence (2 references)
PMID:42166520 SUPPORT Human Clinical
"Onset was lumbar in 94%, proximally predominant."
94% of 78 molecularly confirmed patients maps to VERY_FREQUENT (80-100%), and gives both halves of this term at once — lumbar (lower limb) and proximal. The deep-research artifact proposed the broader HP:0007340 (Lower limb muscle weakness); HP:0008994 is preferred because it is the term that carries both axes the source states.
PMID:42166520 SUPPORT Human Clinical
"ALS8 is a slowly progressive motor neurone disease with lumbar onset, ascending progression, and frequent but subtle UMN signs."
Confirms that the lumbar distribution is the point of onset rather than the permanent extent — the deficit ascends — which is why this is curated alongside, not instead of, the unqualified proximal weakness phenotype.
Camptocormia HP:0100595 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Camptocormia (HP:0100595). HP:0100595 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32383641 SUPPORT Human Clinical
"The clinical features in all patients were camptocormia, fasciculation, and weakness in all limbs."
Documents camptocormia in all affected members of this family.
Reduced Tendon Reflexes HP:0001315 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Reduced tendon reflexes (HP:0001315). HP:0001315 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:16967488 SUPPORT Human Clinical
"Tone and tendon reflexes were decreased and a distal tremor was common."
Documents decreased tone and reflexes in the affected kindred.
Abnormal Pyramidal Signs FREQUENT HP:0007256 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal pyramidal sign (HP:0007256). HP:0007256 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:42166520 SUPPORT Human Clinical
"UMN signs were present in 53 patients; none exhibited clonus."
53 of 78 patients is 68%, which maps to FREQUENT (30-79%).
PMID:42166520 SUPPORT Human Clinical
"At admission, 51% had spinal-onset ALS, 42% progressive muscular atrophy (PMA) and 6% flail leg; 30% of patients with PMA subsequently developed UMN signs."
Shows the pure lower motor neuron presentation is a large minority that partially converts, which is the phenotypic-boundary problem this entry records.
ORPHA:209335 REFUTE Other
"A rare, genetic, motor neuron disease characterized by adulthood-onset of slowly progressive, proximal muscular weakness with fasciculations, amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or pyramidal involvement."
Orphanet defines this entity as excluding pyramidal involvement, so by that definition the phenotype curated here does not belong to it. This is a nosological stance rather than a contrary observation — Orphanet is drawing the SMA/ALS8 boundary at the absence of upper motor neuron signs, while the molecularly confirmed series finds those signs in 53 of 78 p.Pro56Ser carriers. Recorded as REFUTE so the disagreement between the definition and the cohort is visible rather than silently resolved in favour of one.
Dysautonomia Orthostatic hypotension due to autonomic dysfunction HP:0004926 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Orthostatic hypotension due to autonomic dysfunction (HP:0004926). HP:0004926 is a phenotype from the Human Phenotype Ontology.
Sequelae: Constipation
Show evidence (2 references)
PMID:16967488 SUPPORT Human Clinical
"Autonomic abnormalities were also present, including choking, chronic intestinal constipation, sexual dysfunction, and sudomotor abnormalities, and on nerve morphology there was involvement of unmyelinated fibers."
Documents the autonomic syndrome and its unmyelinated-fibre substrate.
PMID:32383641 SUPPORT Human Clinical
"Two patients developed symptoms of dysautonomia, including abdominal bloating, orthostatic hypotension, constipation, frequent urination, decreased sweating, and burning feet."
Independent replication in an unrelated family, including the orthostatic hypotension this phenotype term names.
Bulbar Involvement OCCASIONAL Dysphonia HP:0001618 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dysphonia (HP:0001618). HP:0001618 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:42166520 SUPPORT Human Clinical
"Bulbar involvement occurred in 17 (21.8%) patients, predominantly as dysphonia."
21.8% maps to OCCASIONAL (5-29%), and the paper names dysphonia as the predominant form.
ORPHA:209335 REFUTE Other
"A rare, genetic, motor neuron disease characterized by adulthood-onset of slowly progressive, proximal muscular weakness with fasciculations, amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or pyramidal involvement."
Orphanet's definition of this entity excludes bulbar involvement, which the 21.8% figure from the molecularly confirmed series contradicts. Curated as REFUTE for the same reason as the pyramidal-signs node: the disagreement is between a nosological definition and a genotype-defined cohort, and is the substance of this entry's scope problem.
Loss of Ambulation HP:0002505 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Loss of ambulation (HP:0002505). HP:0002505 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:42166520 SUPPORT Human Clinical
"Survival was 21.9 years; times to wheelchair dependence and noninvasive ventilation were 7.0 and 10.0 years, respectively."
Gives the median time to wheelchair dependence.
🧬

Genetic Associations

1
VAPB
Gene: VAPB hgnc:12649 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is VAPB (hgnc:12649). hgnc:12649 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (4 references)
PMID:15372378 SUPPORT Human Clinical
"Subsequently, the same mutation was identified in patients from six additional kindreds but with different clinical courses, such as ALS8, late-onset SMA, and typical severe ALS with rapid progression."
Establishes gene-disease causation and, in the same sentence, the one-allele-many-phenotypes problem.
PMID:16187141 SUPPORT Human Clinical
"Eight families, comprising more than 1,500 individuals of whom about 200 are affected, are now known to carry this mutation."
Gives the size of the known p.Pro56Ser population and its family structure.
PMID:34440634 SUPPORT Other
"The VAP proteins are integral adaptor proteins of the endoplasmic reticulum (ER) membrane that recruit a myriad of interacting partners to the ER surface."
States the normal molecular function of the affected protein.
+ 1 more reference
💊

Medical Actions

3
Noninvasive Ventilation
Category: Therapeutic Action: noninvasive ventilationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is noninvasive ventilation, annotated with Non-Invasive Mechanical Ventilation (NCIT:C171457). NCIT:C171457 is a clinical intervention from the NCI Thesaurus. Ontology label: Non-Invasive Mechanical Ventilation NCIT:C171457
Ventilatory support, typically bilevel positive airway pressure, once respiratory muscle weakness produces orthostatic breathlessness, orthopnoea or nocturnal hypoventilation. This is the single most consequential supportive intervention in this disorder because respiratory insufficiency is the terminal event, and because the natural history is slow and predictable enough to anticipate: the molecularly confirmed p.Pro56Ser series places the median time from onset to noninvasive ventilation at 10 years, three years after wheelchair dependence. It is not disease-modifying — see the vapb_no_disease_modifying_therapy discussion — and it does not slow denervation.
Mechanism Target:
BYPASSES Respiratory Insufficiency — NIV supplies mechanically the inspiratory pressure that denervated diaphragmatic and intercostal motor units can no longer generate. It works around the failing effector rather than acting anywhere on the upstream VAPB chain, which is why the effect is BYPASSES and why it is compatible with continued progression of the mechanism it compensates for.
Show evidence (1 reference)
PMID:42166520 SUPPORT Human Clinical
"Survival was 21.9 years; times to wheelchair dependence and noninvasive ventilation were 7.0 and 10.0 years, respectively."
Ties the intervention to this disorder's respiratory endpoint on a dated milestone rather than a general indication.
Show evidence (3 references)
PMID:42166520 SUPPORT Human Clinical
"Survival was 21.9 years; times to wheelchair dependence and noninvasive ventilation were 7.0 and 10.0 years, respectively."
Establishes noninvasive ventilation as a milestone actually reached by this p.Pro56Ser cohort, and dates it, which is what makes it curatable here rather than merely plausible by analogy with ALS.
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."
Expert-panel respiratory-care guidance for motor neurone disease naming NIV as the main recognized treatment for the respiratory failure this disorder ends in. PARTIAL, not SUPPORT, on the same ground as the Bourke trial below: the guidance is written for ALS, not for VAPB p.Pro56Ser carriers. ALS8 sits inside that clinical category and 51% of the p.Pro56Ser series presented as spinal-onset ALS, but that is an extrapolation and is tagged as one.
PMID:16426990 SUPPORT Human Clinical
"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."
The controlled evidence that NIV extends survival and preserves quality of life in motor neurone disease. Marked PARTIAL rather than SUPPORT because the trial was in ALS, not in VAPB p.Pro56Ser carriers, and its benefit was confined to the subgroup with better bulbar function — no NIV trial has been run in this disorder, and none is likely at this prevalence.
Physical Therapy and Rehabilitation
Category: Therapeutic Action: Physical TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Physical Therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. NCIT:C15302
Stage-matched rehabilitation — range-of-motion work, gait and transfer training, orthoses, mobility aids and eventually wheelchair provision — aimed at independence, safety and prevention of secondary complications such as contractures and falls. The unusually long course here makes this weigh more than it does in typical ALS: median survival is 21.9 years while wheelchair dependence arrives at 7, so most patients live over a decade with substantial motor disability.
Mechanism Target:
MODULATES Loss of Ambulation — Rehabilitation acts on the functional consequence, not on the denervation producing it: gait training, orthoses and mobility aids alter how much disability a given degree of proximal weakness imposes and when the wheelchair threshold is crossed. MODULATES rather than INHIBITS because no evidence shows rehabilitation slows motor unit loss.
Show evidence (1 reference)
PMID:24510737 SUPPORT Human Clinical
"Given the progressive nature of ALS, the clinician must be aware of the expected disease trajectory and apply appropriate interventions at each stage."
The stage-matched principle that connects the intervention to the ambulation milestone. PARTIAL for the same ALS-versus-ALS8 reason as above.
Show evidence (2 references)
PMID:24510737 SUPPORT Human Clinical
"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."
States the goal and scope of rehabilitation in progressive motor neurone disease. PARTIAL because it is a narrative review addressed to ALS, with no VAPB-specific rehabilitation study to cite; the stage-matched principle transfers, the effect size is not established for this disorder.
PMID:42166520 SUPPORT Human Clinical
"Survival was 21.9 years; times to wheelchair dependence and noninvasive ventilation were 7.0 and 10.0 years, respectively."
The gap between wheelchair dependence at 7 years and death at 21.9 is the disease-specific reason rehabilitation matters here — it quantifies the long period of survival with disability that rehabilitation is addressed to.
Genetic Counseling
Category: Counseling / Informational Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Counselling for an autosomal dominant, adult-onset, fully penetrant-appearing founder allele, where at-risk relatives are typically adults who have already reproduced. The 78-patient natural-history series explicitly frames its own findings as supporting genetic counselling and anticipatory management, which is the practical output of characterizing a course this predictable.
Show evidence (1 reference)
PMID:42166520 SUPPORT Human Clinical
"These findings expand the phenotypic characterization of ALS8 and support genetic counseling and anticipatory management."
The authors' own statement of what the natural-history data are for. No target_mechanisms is set because counselling is a non-therapeutic action and does not act on a pathograph node.
🔬

Diagnosis

2
Electromyography showing chronic denervation and reinnervation
Needle EMG establishes an anterior-horn-cell process: ongoing denervation with reinnervation, large motor unit potentials and reduced recruitment, with preserved sensory responses. This is what separates the disorder from a sensorimotor polyneuropathy and, together with the family history, what prompts genetic testing.
Show evidence (2 references)
PMID:16967488 SUPPORT Human Clinical
"Electromyography disclosed ongoing denervation and reinnervation."
The characteristic electrodiagnostic finding.
PMID:16967488 SUPPORT Human Clinical
"Tone and tendon reflexes were decreased and a distal tremor was common. Sensation was preserved."
Records the lower-motor-neuron exam with preserved sensation, which keeps the diagnosis in the motor neuronopathy column rather than a sensorimotor polyneuropathy.
Molecular testing for VAPB in non-5q spinal muscular atrophy
After SMN1 deletion has been excluded, VAPB is one of the genes on the non-5q SMA / hereditary motor neuropathy panel. Diagnostic yield in this group is modest and lowest in exactly the presentation this disorder produces — pure proximal weakness — so a negative panel does not close the question.
Show evidence (2 references)
PMID:37470033 SUPPORT Human Clinical
"The genetic diagnostic yield was lowest in P-SMA (6/21, 28.6%) compared with PD-SMA (16/35, 45.7%) and SP-SMA (10/15, 66.7%)."
Quantifies the diagnostic difficulty of the pure proximal non-5q SMA presentation.
PMID:37470033 SUPPORT Human Clinical
"Non-5q SMA is genetically heterogeneous, and neuropathy gene panels achieve a molecular diagnosis in one-third of the patients."
States the overall panel yield in the differential category this disorder belongs to.
📈

Progression

1
Slowly progressive ascending course
Age: onset in the fifth decade
Onset is insidious in the fifth decade, lumbar and proximal. Weakness ascends; wheelchair dependence follows at a median of 7 years and noninvasive ventilation at 10 years, but median survival is 21.9 years — an order of magnitude longer than typical ALS. Mortality is nonetheless elevated, with a standardized mortality ratio of 4.54. Upper motor neuron status does not affect survival.
Show evidence (2 references)
PMID:42166520 SUPPORT Human Clinical
"ALS8 is a slowly progressive motor neurone disease with lumbar onset, ascending progression, and frequent but subtle UMN signs."
The authors' own summary of the course.
PMID:42166520 SUPPORT Human Clinical
"UMN status did not affect survival (p = 0.312). The standardized mortality ratio was 4.54 (95% CI 2.77-7.01), supporting disease-related excess mortality."
Quantifies excess mortality and shows the UMN/LMN split is not prognostically separating.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
No population-based prevalence or incidence estimate exists. The largest enumeration is of the founder p.Pro56Ser population: eight families totalling more than 1,500 individuals of whom about 200 were affected, with a later clinical series assembling 78 molecularly confirmed patients from 57 apparently unrelated families. These are pedigree counts, heavily enriched for Brazilian families of Portuguese ancestry, and cannot be converted into a population rate.
Show evidence (2 references)
PMID:16187141 SUPPORT Human Clinical
"Eight families, comprising more than 1,500 individuals of whom about 200 are affected, are now known to carry this mutation."
The affected-case enumeration behind the CASES_IN_LITERATURE measure.
PMID:42166520 SUPPORT Human Clinical
"We retrospectively analyzed 78 patients with ALS8 confirmed via molecular testing or familial linkage analysis from 57 apparently unrelated families."
The largest molecularly confirmed series, again a case count rather than a rate.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Adult-Onset Proximal Spinal Muscular Atrophy, Autosomal Dominant:

Amyotrophic lateral sclerosis
Overlapping Features Not a clean differential so much as a continuum: the same VAPB p.Pro56Ser allele produces late-onset SMA, atypical slowly progressive ALS, and rapidly progressive typical ALS in different kindreds, and most ALS8 patients eventually show subtle pyramidal signs. Distinguishing them matters prognostically — median survival here is 21.9 years — but the boundary is clinical, not molecular.
Show evidence (1 reference)
PMID:15372378 SUPPORT Human Clinical
"Subsequently, the same mutation was identified in patients from six additional kindreds but with different clinical courses, such as ALS8, late-onset SMA, and typical severe ALS with rapid progression."
Establishes that SMA and ALS presentations share the identical allele.
Other non-5q spinal muscular atrophies and hereditary motor neuropathies
Overlapping Features BICD2, DYNC1H1, TRPV4, VCP, HSPB1, VRK1, DNAJB2, MORC2, ASAH1, HEXB and the androgen receptor (Kennedy disease) all produce adult proximal or proximal-distal motor neuronopathy phenotypes. In a French/UK series of 71 non-5q SMA patients, BICD2 and DYNC1H1 were the commonest causes found.
Show evidence (1 reference)
PMID:37470033 SUPPORT Human Clinical
"Thirty-two patients (45.1%) had a genetic diagnosis: BICD2 (n = 9), DYNC1H1 (n = 7), TRPV4 (n = 4), VCP, HSBP1, AR (n = 2), VRK1, DNAJB2, MORC2, ASAH1, HEXB, and unexpectedly, COL6A3 (n = 1)."
Enumerates the genes competing for this clinical phenotype.
🧫

Experimental Models

1
ALS8 patient-derived iPSC motor neurons IPSC_DERIVED_MODEL
Fibroblasts from p.Pro56Ser patients and their non-carrier siblings reprogrammed to iPSC and differentiated into motor neurons — the closest available human-cell model, with sibling controls.
Publication
PMID:21685205
Pathograph links
Loss of Functional VAPB at ER Membrane Contact Sites measures fidelity: high VAPB protein is reduced in patient-derived motor neurons relative to non-carrier siblings, at endogenous expression levels.
Limitations: iPSC-derived motor neurons are developmentally immature and cannot model a disorder whose onset is in the fifth decade; the reduction is a molecular readout, not a degeneration phenotype.
Readouts
VAPB protein level in patient motor neurons
Direction: DECREASED
Interpretation: Reduced VAPB in human patient motor neurons, supporting a functional shortfall of the protein as the convergent effector.
Show evidence (1 reference)
PMID:21685205 SUPPORT In Vitro
"We show for the first time that VAPB protein levels are reduced in ALS8-derived motor neurons but, in contrast to over-expression systems, cytoplasmic aggregates could not be identified."
The measurement behind this readout, and its explicit contrast with overexpression systems.
🐁

Animal Models

3
Vapb P56S knock-in mouse
The most physiologic rodent model: the endogenous Vapb locus carries the P56S change, so expression level and tissue distribution are normal. Heterozygotes — the human genotype — show mild age-dependent motor deficits; homozygotes are worse, giving a dose-response consistent with the dominant human allele.
Species
Mouse
Genotype
Vapb p.Pro56Ser knock-in (heterozygous and homozygous)
Publication
PMID:26362257
Pathograph links
ER Stress and Unfolded Protein Response Activation recapitulates fidelity: moderate ER stress and an autophagic response appear in motor neurons before behavioural deficits, at physiological expression level.
Limitations: The behavioural phenotype is mild and late; the model does not reproduce the severe weakness or the respiratory failure that ends the human disease, so it informs the initiating steps rather than the clinical endpoint.
Readouts
ER stress markers in motor neurons
Direction: INCREASED
Interpretation: Induction of ER stress precedes overt motor behavioural defects, positioning this node upstream in the chain.
Show evidence (1 reference)
PMID:26362257 SUPPORT Model Organism
"The mutant mice demonstrate induction of ER stress and autophagic response in motor neurons before obvious onset of behavioral defects, suggesting that these cellular biological defects might contribute to the initiation of the disease."
The measurement behind this readout and its temporal ordering.
Show evidence (1 reference)
PMID:26362257 SUPPORT Model Organism
"Heterozygous P56S Vapb knock-in mice show mild age-dependent defects in motor behaviors as characteristic features of the disease."
Supports treating the heterozygous knock-in as informative for the human heterozygous disease.
ER-Derived Aggregation of Misfolded VAPB recapitulates fidelity: moderate Cytoplasmic inclusions containing P56S VAPB and ubiquitinated protein form selectively in motor neurons at physiological expression level — the counter-observation to the claim that aggregates are purely an overexpression artefact.
Limitations: Aggregation in mouse motor neurons does not settle whether aggregates form in human motor neurons, where the observation has not been made.
Show evidence (1 reference)
PMID:26362257 SUPPORT Model Organism
"Significantly, the knock-in mice demonstrate accumulation of P56S VAPB protein and ubiquitinated proteins in cytoplasmic inclusions, selectively in motor neurons."
Documents aggregation without overexpression.
Thy1.2 P56S VAPB transgenic mouse
Pan-neuronal overexpression of human P56S VAPB. Instructive precisely because its cell-type selectivity is the opposite of the human Finkel phenotype: corticospinal motor neurons are progressively lost while spinal motor neurons survive with functional impairment.
Species
Mouse
Genotype
Thy1.2-driven pan-neuronal human VAPB p.Pro56Ser transgene
Publication
PMID:23771029
Pathograph links
Lower Motor Neuron Degeneration partially recapitulates fidelity: low Spinal motor neurons show altered C-bouton morphology and impaired spontaneous rhythmic discharge, but do not die; the population that dies is the corticospinal one.
Limitations: The human disorder curated here is defined by lower motor neuron loss with no upper motor neuron signs. This model inverts that, and its transgene is overexpressed under a heterologous promoter, so it cannot be used to argue about which motor neuron population is vulnerable in patients.
Readouts
Spinal motor neuron survival
Direction: UNCHANGED
Interpretation: A negative result: spinal motor neuron number was preserved despite progressive corticospinal loss.
Show evidence (1 reference)
PMID:23771029 SUPPORT Model Organism
"However, only a progressive loss of CSMNs but not SMNs was found in P56S VAPB Tg mice."
The survival measurement behind this readout.
Show evidence (1 reference)
PMID:23771029 SUPPORT Model Organism
"While WT VAPB Tg mice did not exhibit any overt motor behavioral phenotypes, P56S VAPB Tg mice developed progressive hyperactivities and other motor abnormalities."
Establishes an allele-specific motor phenotype while the accompanying limitation records why its cell-type pattern does not match the human disorder.
Vapb knockout mouse
A direct test of the haploinsufficiency hypothesis: if losing VAPB function were sufficient, a null mouse should develop motor neuron disease. It largely does not.
Species
Mouse
Genotype
Vapb null (complete loss of Vapb expression)
Publication
PMID:23446633
Pathograph links
Lower Motor Neuron Degeneration fails to recapitulate fidelity: moderate Complete loss of Vapb produced only mild motor deficits after 18 months and left neuromuscular junctions innervated — no motor neuron disease.
Limitations: This is a null, not the human heterozygous missense genotype, and mouse lifespan may be too short for a disorder with a 45-year human onset. It therefore constrains rather than refutes the loss-of-function hypothesis: loss of VAPB function alone is insufficient in mouse, which is compatible with it being necessary but requiring the additional dominant-negative component.
Show evidence (1 reference)
PMID:23446633 REFUTE Model Organism
"Mice knocked-out for Vapb showed mild motor deficits after 18 months of age yet had innervated neuromuscular junctions (NMJs)."
The negative result: complete VAPB loss does not reproduce motor neuron degeneration or denervation in mouse.
{ }

Source YAML

click to show 
name: Adult-Onset Proximal Spinal Muscular Atrophy, Autosomal Dominant
creation_date: "2026-08-27T00:00:00Z"
description: >-
  Adult-onset proximal spinal muscular atrophy, autosomal dominant — the Finkel
  type of late-onset SMA — is a dominantly inherited lower motor neuron disease
  caused by heterozygous variation in VAPB, in nearly every reported family the
  recurrent p.Pro56Ser allele. Onset is in mid-adult life with proximal,
  lumbar-predominant weakness and neurogenic muscle atrophy that ascends slowly
  over decades. VAPB is an integral endoplasmic reticulum adaptor that builds
  membrane contact sites between the ER and essentially every other organelle;
  p.Pro56Ser sits in its major sperm protein (MSP) domain and renders the
  protein unstable, aggregation-prone and non-functional.

  The entity's defining curatorial problem is that the same allele does not
  produce one disease. The 2004 discovery paper found p.Pro56Ser in seven
  kindreds presenting variously as late-onset SMA, as atypical slowly
  progressive ALS (ALS8), and as typical rapidly progressive ALS; a 2026 series
  of 78 molecularly confirmed patients found that 42% presented as pure lower
  motor neuron progressive muscular atrophy while a majority eventually showed
  subtle upper motor neuron signs. This entry is scoped to the pure lower motor
  neuron, proximal-onset end of that spectrum, and records the continuity with
  ALS8 explicitly rather than pretending to a clean boundary.
category: Mendelian
parents:
- hereditary disease
- Motor Neuron Disease
- Neuromuscular Disease
synonyms:
- Finkel disease
- Finkel-type spinal muscular atrophy
- spinal muscular atrophy, late-onset, Finkel type
- autosomal dominant late-onset spinal muscular atrophy, Finkel type
- autosomal dominant adult-onset proximal SMA
- SMAFK
- VAPB-related spinal muscular atrophy
disease_term:
  preferred_term: adult-onset proximal spinal muscular atrophy, autosomal dominant
  term:
    id: MONDO:0008453
    label: adult-onset proximal spinal muscular atrophy, autosomal dominant
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:15372378
      reference_title: "A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Motor neuron diseases (MNDs) are a group of neurodegenerative disorders
        with involvement of upper and/or lower motor neurons, such as amyotrophic
        lateral sclerosis (ALS), spinal muscular atrophy (SMA), progressive bulbar
        palsy, and primary lateral sclerosis.
      explanation: >-
        Places the entity among the motor neuron diseases, a neurologic disorder
        class.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:15372378
      reference_title: "A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Here, we report the finding of a novel missense mutation in the
        vesicle-associated membrane protein/synaptobrevin-associated membrane
        protein B (VAPB) gene in patients from this family.
      explanation: >-
        Establishes a single-gene Mendelian basis for the disorder.
mappings:
  icd10cm_mappings:
  - term:
      id: ICD10CM:G12.1
      label: Other inherited spinal muscular atrophy
    mapping_predicate: skos:broadMatch
    mapping_source: ORPHA:209335
    mapping_justification: semapv:ManualMappingCuration
    notes: >-
      Taken from the Orphanet cross-reference table for ORPHA:209335, the
      exact-match ORDO term for MONDO:0008453. broadMatch, not exact: G12.1 is a
      billing-level residual bucket whose own synonym list spans distal SMA,
      scapuloperoneal SMA, Kugelberg-Welander and Fazio-Londe, so it contains
      this entity many times over rather than naming it.
  icd11f_mappings:
  - term:
      id: icd11f:353473981
      label: Autosomal dominant proximal spinal muscular atrophy
    mapping_predicate: skos:broadMatch
    mapping_justification: semapv:ManualMappingCuration
    notes: >-
      Deliberately NOT the ICD-11 code Orphanet lists (8B61.Y). That is a
      linearization code, and the icd11f dynamic enum this slot binds to keys on
      numeric ICD-11 Foundation entity ids, which neither the Orphanet record nor
      MONDO:0008453 supplies -- MONDO carries no icd11.foundation xref at all.
      icd11f:353473981 is the Foundation entity whose label matches this entity's
      defining features; it is broader because it also subsumes
      icd11f:1205775957, the childhood-onset sibling, while this entry is
      adult-onset only.
references:
- reference: PMID:15372378
  title: "A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis."
- reference: PMID:16187141
  title: "A common founder for amyotrophic lateral sclerosis type 8 (ALS8) in the Brazilian population."
- reference: PMID:16967488
  title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
- reference: PMID:42166520
  title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
- reference: PMID:32383641
  title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
- reference: PMID:34440634
  title: "The Link between VAPB Loss of Function and Amyotrophic Lateral Sclerosis."
- reference: PMID:17804640
  title: "Motor neuron disease-associated mutant vesicle-associated membrane protein-associated protein (VAP) B recruits wild-type VAPs into endoplasmic reticulum-derived tubular aggregates."
- reference: PMID:24252306
  title: "Amyotrophic lateral sclerosis (ALS)-associated VAPB-P56S inclusions represent an ER quality control compartment."
- reference: PMID:18555774
  title: "The amyotrophic lateral sclerosis 8 protein VAPB is cleaved, secreted, and acts as a ligand for Eph receptors."
- reference: PMID:22131369
  title: "VAPB interacts with the mitochondrial protein PTPIP51 to regulate calcium homeostasis."
- reference: PMID:24893131
  title: "ER-mitochondria associations are regulated by the VAPB-PTPIP51 interaction and are disrupted by ALS/FTD-associated TDP-43."
- reference: PMID:33972508
  title: "Pathomechanisms of ALS8: altered autophagy and defective RNA binding protein (RBP) homeostasis due to the VAPB P56S mutation."
- reference: PMID:26362257
  title: "Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response."
- reference: PMID:23771029
  title: "Amyotrophic lateral sclerosis-related VAPB P56S mutation differentially affects the function and survival of corticospinal and spinal motor neurons."
- reference: PMID:23446633
  title: "Investigating the contribution of VAPB/ALS8 loss of function in amyotrophic lateral sclerosis."
- reference: PMID:21685205
  title: "Downregulation of VAPB expression in motor neurons derived from induced pluripotent stem cells of ALS8 patients."
- reference: PMID:24271015
  title: "The amyotrophic lateral sclerosis 8 protein, VAP, is required for ER protein quality control."
- reference: PMID:39870504
  title: "A role for mitochondria-ER crosstalk in amyotrophic lateral sclerosis 8 pathogenesis."
- reference: PMID:33461946
  title: "Deregulation of phosphatidylinositol-4-phosphate in the development of amyotrophic lateral sclerosis 8."
- reference: PMID:18701194
  title: "Vesicle associated membrane protein B (VAPB) is decreased in ALS spinal cord."
- reference: PMID:37470033
  title: "Phenotype Presentation and Molecular Diagnostic Yield in Non-5q Spinal Muscular Atrophy."
- reference: PMID:34133501
  title: "The history behind ALS type 8: from the first phenotype description to the discovery of VAPB mutation."
- reference: PMID:20301623
  title: "Amyotrophic Lateral Sclerosis Overview."
  tags:
  - GeneReviews
- reference: ORPHA:209335
  title: "Autosomal dominant adult-onset proximal spinal muscular atrophy"
inheritance:
- name: Autosomal dominant inheritance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    A single heterozygous VAPB p.Pro56Ser allele is sufficient. The disorder was
    mapped in a large Brazilian kindred and the same variant then found in six
    further kindreds; haplotype analysis across eight families of both
    Portuguese-Brazilian and African-Brazilian ancestry places the origin in a
    single founding event, so most of the world's reported patients share one
    ancestral chromosome rather than representing independent mutational events.
  evidence:
  - reference: PMID:15372378
    reference_title: "A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequently, the same mutation was identified in patients from six
      additional kindreds but with different clinical courses, such as ALS8,
      late-onset SMA, and typical severe ALS with rapid progression.
    explanation: >-
      Documents segregation of a single heterozygous allele across seven
      kindreds, including the late-onset SMA presentation this entry curates.
  - reference: PMID:16187141
    reference_title: "A common founder for amyotrophic lateral sclerosis type 8 (ALS8) in the Brazilian population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Haplotype analysis shows a common founder for all families regardless of
      ancestry, with a founding event 23 generations ago (95% CI 13-39),
      consistent with the Portuguese colonization of Brazil.
    explanation: >-
      Establishes the founder origin, which is why allele counts across families
      cannot be treated as independent observations.
pathophysiology:
- name: VAPB p.Pro56Ser MSP-Domain Variant
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: ESTABLISHED
  description: >-
    A heterozygous germline missense change substitutes serine for a conserved
    proline at residue 56 of VAPB, within the N-terminal major sperm protein
    (MSP) homology domain — the surface through which VAPB binds FFAT-motif
    partners and so recruits lipid-transfer and other proteins to the cytosolic
    face of the endoplasmic reticulum. Essentially every reported family carries
    this one allele, inherited from a common founder.
  genes:
  - preferred_term: VAPB
    term:
      id: hgnc:12649
      label: VAPB
  genetic_context:
    variant_origin: GERMLINE
    zygosity: HETEROZYGOUS
    description: >-
      Heterozygous germline missense variant in the MSP domain. The functional
      impact category is deliberately left unset: whether the dominant action is
      a toxic gain of function through aggregation and sequestration of the
      wild-type protein, or loss of function of the remaining wild-type allele,
      is the unresolved question recorded in this entry's mechanistic_hypotheses.
  evidence:
  - reference: PMID:15372378
    reference_title: "A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report the finding of a novel missense mutation in the
      vesicle-associated membrane protein/synaptobrevin-associated membrane
      protein B (VAPB) gene in patients from this family.
    explanation: >-
      The original identification of the causal VAPB variant.
  - reference: PMID:17804640
    reference_title: "Motor neuron disease-associated mutant vesicle-associated membrane protein-associated protein (VAP) B recruits wild-type VAPs into endoplasmic reticulum-derived tubular aggregates."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      A genetic mutation (P56S) in the conserved major sperm protein homology
      domain of VAPB has been linked to motor-neuron degeneration in affected
      amyotrophic lateral sclerosis (ALS) patients.
    explanation: >-
      Locates the variant in the conserved MSP homology domain, which is what
      makes the FFAT-binding surface the affected function.
  downstream:
  - target: ER-Derived Aggregation of Misfolded VAPB
  - target: Loss of Functional VAPB at ER Membrane Contact Sites
- name: ER-Derived Aggregation of Misfolded VAPB
  biological_scale: CELLULAR
  role: intermediate
  mechanism_confidence: ESTABLISHED
  conforms_to: "loss_of_proteostasis#Misfolded-Protein Aggregation"
  description: >-
    Mutant VAPB misfolds and self-associates into immobile, tubular ER-derived
    inclusions in motor neurons, dragging endogenous wild-type VAPA and VAPB into
    the same aggregates. The inclusions are not inert: they are decorated with
    ER-associated degradation machinery (p97/VCP, Derlin-1, BAP31) and behave as
    a quality-control compartment formed when misfolded VAPB exceeds ERAD
    capacity. Their pathogenic weight is contested — see the
    HUMAN_MODEL_MISMATCH discussion below, since patient-derived motor neurons
    expressing the allele at physiological level do not show them.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: protein folding
    modifier: ABNORMAL
    term:
      id: GO:0006457
      label: protein folding
  evidence:
  - reference: PMID:17804640
    reference_title: "Motor neuron disease-associated mutant vesicle-associated membrane protein-associated protein (VAP) B recruits wild-type VAPs into endoplasmic reticulum-derived tubular aggregates."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We report that in the CNS, VAPB is abundant in motor neurons and that the
      P56S substitution causes aggregation of mutant VAPB in immobile tubular ER
      clusters, perturbs FFAT-motif binding, and traps endogenous VAP in mutant
      aggregates.
    explanation: >-
      Documents both the aggregation itself and the sequestration of wild-type
      VAP that underlies the dominant-negative reading of the mechanism.
  - reference: PMID:24252306
    reference_title: "Amyotrophic lateral sclerosis (ALS)-associated VAPB-P56S inclusions represent an ER quality control compartment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The data indicate that the VAPB-P56S inclusions represent a novel reversible
      ER quality control compartment that is formed when the amount of mutant VAPB
      exceeds the capacity of the ERAD pathway and that isolates misfolded and
      aggregated VAPB from the rest of the ER.
    explanation: >-
      Characterizes the inclusions as an ERAD-linked quality-control compartment
      and, importantly, argues they may be protective rather than toxic —
      PARTIAL because it supports the existence of the node while qualifying its
      causal role.
  - reference: PMID:24252306
    reference_title: "Amyotrophic lateral sclerosis (ALS)-associated VAPB-P56S inclusions represent an ER quality control compartment."
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The presence of these inclusions does not correlate with signs of axonal and
      neuronal degeneration, and axotomy leads to their gradual disappearance,
      indicating that they represent reversible structures.
    explanation: >-
      Directly refutes a simple aggregate-causes-degeneration reading in the
      transgenic mouse: inclusion burden and degeneration are uncoupled.
  downstream:
  - target: Loss of Functional VAPB at ER Membrane Contact Sites
  - target: ER Stress and Unfolded Protein Response Activation
- name: Loss of Functional VAPB at ER Membrane Contact Sites
  biological_scale: MOLECULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  description: >-
    However the aggregates are read, the functional consequence converges on too
    little working VAPB at the ER surface. The mutant protein is unstable and
    non-functional, and VAPB levels are reduced in patient-derived motor neurons
    and in ALS spinal cord. Because VAPB is the tether that recruits FFAT-motif
    partners to the ER, its shortfall degrades a whole family of contact-site
    functions at once: ER-to-Golgi transport, lipid exchange (with a
    characteristic rise in phosphatidylinositol-4-phosphate), phosphoinositide
    and calcium handling, and ER protein quality control.
  biological_processes:
  - preferred_term: intermembrane lipid transfer
    modifier: DECREASED
    term:
      id: GO:0120009
      label: intermembrane lipid transfer
  - preferred_term: endoplasmic reticulum to Golgi vesicle-mediated transport
    modifier: DECREASED
    term:
      id: GO:0006888
      label: endoplasmic reticulum to Golgi vesicle-mediated transport
  evidence:
  - reference: PMID:34440634
    reference_title: "The Link between VAPB Loss of Function and Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The mutant protein is aggregation-prone, non-functional and unstable, and
      its expression from a single allele appears to be insufficient to support
      toxic gain-of-function effects within motor neurons.
    explanation: >-
      States the loss-of-function reading of the allele that this node
      represents.
  - reference: PMID:21685205
    reference_title: "Downregulation of VAPB expression in motor neurons derived from induced pluripotent stem cells of ALS8 patients."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We show for the first time that VAPB protein levels are reduced in
      ALS8-derived motor neurons but, in contrast to over-expression systems,
      cytoplasmic aggregates could not be identified.
    explanation: >-
      Demonstrates reduced VAPB in patient-derived motor neurons — the direct
      human-cell evidence for this node, and simultaneously the observation that
      the aggregate node is not seen at physiological expression.
  - reference: PMID:18701194
    reference_title: "Vesicle associated membrane protein B (VAPB) is decreased in ALS spinal cord."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Expression of VAPB mRNA and protein was predominantly localised to large
      motor neurones further supporting the relevance of this finding to disease
      progression occurring in SALS.
    explanation: >-
      Localizes VAPB expression to large motor neurons in human spinal cord,
      which is why a VAPB shortfall is cell-type selective. Note this cohort is
      sporadic ALS, not VAPB-mutant disease.
  - reference: PMID:33461946
    reference_title: "Deregulation of phosphatidylinositol-4-phosphate in the development of amyotrophic lateral sclerosis 8."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      One prominent function mediated by VAPB at these sites is lipid exchange,
      and a recurrent phenotype observed in all models investigating knockout or
      knockdown of VAPs is a significant increase in the levels of
      phosphatidylinositol-4-phosphate (PI4P).
    explanation: >-
      Names the lipid-exchange function lost and the PI4P readout that recurs
      across VAP-deficient models.
  downstream:
  - target: ER Stress and Unfolded Protein Response Activation
  - target: Disrupted ER-Mitochondria Contact and Calcium Handling
  - target: Impaired Autophagic Flux and RNA-Binding Protein Mislocalization
  - target: Autonomic and Unmyelinated Small-Fibre Degeneration
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      VAPB is not motor-neuron-specific, so the same functional shortfall is
      the presumed cause of the autonomic and small-fibre arm. The intermediates
      are unknown: nothing in this literature explains why some carriers develop
      dysautonomia and most do not, and no cell-type-selective mechanism has
      been proposed.
- name: ER Stress and Unfolded Protein Response Activation
  biological_scale: CELLULAR
  role: intermediate
  mechanism_confidence: ESTABLISHED
  description: >-
    Loss of VAPB-dependent ER quality control and accumulation of misfolded
    VAPB together activate the ER stress response in motor neurons. In
    physiological-level knock-in mice this is detectable before any behavioural
    deficit, which is what makes it a candidate initiating step rather than an
    end-stage epiphenomenon.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: response to endoplasmic reticulum stress
    modifier: INCREASED
    term:
      id: GO:0034976
      label: response to endoplasmic reticulum stress
  - preferred_term: endoplasmic reticulum unfolded protein response
    modifier: INCREASED
    term:
      id: GO:0030968
      label: endoplasmic reticulum unfolded protein response
  evidence:
  - reference: PMID:26362257
    reference_title: "Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The mutant mice demonstrate induction of ER stress and autophagic response
      in motor neurons before obvious onset of behavioral defects, suggesting that
      these cellular biological defects might contribute to the initiation of the
      disease.
    explanation: >-
      Places ER stress upstream of motor deficits at physiological expression
      levels.
  - reference: PMID:24271015
    reference_title: "The amyotrophic lateral sclerosis 8 protein, VAP, is required for ER protein quality control."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Loss of Vap in flies shows various ERQC associated defects, including
      protein accumulation, ER expansion, and ER stress.
    explanation: >-
      Establishes that losing VAP function is by itself sufficient to produce ER
      stress, linking this node to the loss-of-function arm rather than only to
      aggregation.
  - reference: PMID:18555774
    reference_title: "The amyotrophic lateral sclerosis 8 protein VAPB is cleaved, secreted, and acts as a ligand for Eph receptors."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The P58S mutation in VAP33 leads to a failure to secrete the MSP domain as
      well as ubiquitination, accumulation of inclusions in the endoplasmic
      reticulum, and an unfolded protein response.
    explanation: >-
      The Drosophila orthologue of the human variant produces ER inclusions and a
      UPR, and additionally fails to secrete the MSP domain — a distinct
      signalling loss noted here rather than curated as its own chain node
      because it is invertebrate-only evidence.
  downstream:
  - target: Lower Motor Neuron Degeneration
- name: Disrupted ER-Mitochondria Contact and Calcium Handling
  biological_scale: CELLULAR
  role: intermediate
  mechanism_confidence: PROVISIONAL
  description: >-
    VAPB is a mitochondria-associated-membrane protein that tethers ER to
    mitochondria by binding the outer-mitochondrial-membrane protein PTPIP51,
    and this contact is where calcium released from ER stores is taken up by
    mitochondria. p.Pro56Ser alters PTPIP51 binding and increases mitochondrial
    calcium uptake. PROVISIONAL rather than ESTABLISHED because the direct
    evidence comes from overexpression in cell lines and from yeast and
    mammalian model systems, not from VAPB-mutant human motor neurons.
  biological_processes:
  - preferred_term: mitochondrial calcium ion homeostasis
    modifier: ABNORMAL
    term:
      id: GO:0051560
      label: mitochondrial calcium ion homeostasis
  evidence:
  - reference: PMID:22131369
    reference_title: "VAPB interacts with the mitochondrial protein PTPIP51 to regulate calcium homeostasis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Finally, we demonstrate that VAPBP56S has altered binding to PTPIP51 and
      increases Ca(2+) uptake by mitochondria following release from ER stores.
    explanation: >-
      Direct evidence that the disease allele changes the ER-mitochondria tether
      and its calcium function.
  - reference: PMID:24893131
    reference_title: "ER-mitochondria associations are regulated by the VAPB-PTPIP51 interaction and are disrupted by ALS/FTD-associated TDP-43."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Here we show that the ER-resident protein VAPB interacts with the
      mitochondrial protein tyrosine phosphatase-interacting protein-51 (PTPIP51)
      to regulate ER-mitochondria associations.
    explanation: >-
      Establishes the tethering function that the disease allele perturbs.
  - reference: PMID:39870504
    reference_title: "A role for mitochondria-ER crosstalk in amyotrophic lateral sclerosis 8 pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Inclusion formation was found to be a developmentally regulated process
      linked to mitochondrial damage that could be attenuated by reducing
      ER-mitochondrial contacts.
    explanation: >-
      Reverses the expected direction of the arrow: mitochondrial damage feeds
      back on inclusion formation through the same contacts, so this node is part
      of a loop rather than a one-way step.
  downstream:
  - target: Lower Motor Neuron Degeneration
- name: Impaired Autophagic Flux and RNA-Binding Protein Mislocalization
  biological_scale: CELLULAR
  role: intermediate
  mechanism_confidence: PROVISIONAL
  description: >-
    p.Pro56Ser disturbs both the initiation and the completion of autophagy,
    with autophagosomes failing to fuse with lysosomes. Aggregates accumulate
    together with LC3 and p62 and sequester RNA-binding proteins — phosphorylated
    TDP-43, FUS and Matrin 3 — into persistent stress granules, connecting this
    disorder to the wider TDP-43 proteinopathy of ALS. The human material is a
    single ALS8 index patient's muscle biopsy and fibroblasts, which is why the
    node is PROVISIONAL.
  biological_processes:
  - preferred_term: macroautophagy
    modifier: DECREASED
    term:
      id: GO:0016236
      label: macroautophagy
  evidence:
  - reference: PMID:33972508
    reference_title: "Pathomechanisms of ALS8: altered autophagy and defective RNA binding protein (RBP) homeostasis due to the VAPB P56S mutation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Detailed investigations of autophagic flux in cell culture models revealed
      that P56S-VAPB alters both initial and late steps of the autophagy pathway.
    explanation: >-
      Documents the autophagic-flux defect this node represents.
  - reference: PMID:33972508
    reference_title: "Pathomechanisms of ALS8: altered autophagy and defective RNA binding protein (RBP) homeostasis due to the VAPB P56S mutation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Autophagy and RBP homeostasis are interdependent, as demonstrated by the
      cytoplasmic mis-localisation of several RBPs including pTDP-43, FUS, Matrin
      3 which often sequestered with P56S-VAPB aggregates both in cell culture and
      in the muscle biopsy of the ALS8 patient.
    explanation: >-
      Links the autophagic defect to RNA-binding-protein mislocalization,
      including in human patient tissue.
  downstream:
  - target: Lower Motor Neuron Degeneration
- name: Lower Motor Neuron Degeneration
  biological_scale: CELLULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  conforms_to: "loss_of_proteostasis#Proteotoxic Cell Dysfunction and Neurodegeneration"
  description: >-
    Anterior-horn and brainstem lower motor neurons become dysfunctional and
    degenerate. Selectivity is striking and only partly explained: VAPB is
    abundant in motor neurons, and in the pan-neuronal transgenic mouse the
    corticospinal population is lost while spinal motor neurons instead show
    altered C-bouton morphology and impaired rhythmic discharge without frank
    loss. In humans the clinical picture at the Finkel end of the spectrum is
    purely lower motor neuron, whereas subtle pyramidal signs appear in a
    majority of ALS8 patients overall.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: neuron apoptotic process
    modifier: INCREASED
    term:
      id: GO:0051402
      label: neuron apoptotic process
  evidence:
  - reference: PMID:23771029
    reference_title: "Amyotrophic lateral sclerosis-related VAPB P56S mutation differentially affects the function and survival of corticospinal and spinal motor neurons."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      However, only a progressive loss of CSMNs but not SMNs was found in P56S
      VAPB Tg mice.
    explanation: >-
      Supports motor neuron vulnerability while explicitly qualifying it: in this
      model the spinal motor neurons that define the human Finkel phenotype did
      not die.
  - reference: PMID:23771029
    reference_title: "Amyotrophic lateral sclerosis-related VAPB P56S mutation differentially affects the function and survival of corticospinal and spinal motor neurons."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In SMNs, P56S VAPB promoted a rather selective translocation of VAPB protein
      onto the postsynaptic site of C-boutons that altered the morphology of
      C-boutons and impaired the spontaneous rhythmic discharges of SMNs.
    explanation: >-
      Gives the spinal motor neuron a dysfunction phenotype short of death,
      which is consistent with the very slow human course.
  - reference: PMID:26362257
    reference_title: "Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Significantly, the knock-in mice demonstrate accumulation of P56S VAPB
      protein and ubiquitinated proteins in cytoplasmic inclusions, selectively in
      motor neurons.
    explanation: >-
      Establishes motor neuron selectivity of the cellular pathology at
      physiological expression level.
  downstream:
  - target: Chronic Denervation and Reinnervation of Skeletal Muscle
  - target: Reduced Tendon Reflexes
    causal_link_type: DIRECT
    description: >-
      Loss of the efferent limb of the monosynaptic stretch reflex. This is why
      reflexes are reduced or absent rather than brisk, and it is the sign that
      keeps the bedside picture in the lower motor neuron column.
  - target: Bulbar Involvement
    causal_link_type: DIRECT
    description: >-
      Extension of the same anterior-horn process to brainstem lower motor
      neurons. Because it is the bulbar motor nucleus rather than the
      corticobulbar tract that fails, the resulting deficit is predominantly
      dysphonia rather than the spastic dysarthria of bulbar-onset ALS.
- name: Chronic Denervation and Reinnervation of Skeletal Muscle
  biological_scale: TISSUE
  role: intermediate
  mechanism_confidence: ESTABLISHED
  description: >-
    Failing motor neurons denervate their muscle fibres; surviving units sprout
    and reinnervate them, which is why electromyography in these patients shows
    ongoing denervation together with reinnervation rather than acute
    denervation alone. This compensation is what buys the disorder its decades-long
    course, and its eventual exhaustion is what produces clinically apparent
    weakness.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Electromyography disclosed ongoing denervation and reinnervation.
    explanation: >-
      Direct human electrophysiological evidence for this node.
  - reference: PMID:32383641
    reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Electromyography showed widespread neuropathic damage.
    explanation: >-
      Independent replication of the neurogenic electrodiagnostic pattern in an
      unrelated p.Pro56Ser family outside Brazil.
  downstream:
  - target: Proximal Neurogenic Weakness and Muscle Atrophy
  - target: Fasciculations
    causal_link_type: DIRECT
    description: >-
      Spontaneous discharge of unstable, partly denervated motor units — the
      clinical surface of the denervation-reinnervation process this node
      describes.
    evidence:
    - reference: PMID:32383641
      reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The clinical features in all patients were camptocormia, fasciculation,
        and weakness in all limbs.
      explanation: >-
        Reports fasciculation alongside the widespread neuropathic EMG damage
        that defines this node, in the same patients.
  - target: Neurogenic Muscle Atrophy
    causal_link_type: DIRECT
    description: >-
      Muscle fibres that lose their motor neuron and are not recaptured by a
      sprouting neighbour atrophy, giving the grouped-fibre pattern of a
      neurogenic rather than myopathic process.
  - target: Distal Tremor
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Enlarged reinnervated motor units firing with reduced rate modulation
    description: >-
      Postural tremor attributed to the enlarged motor units produced by
      collateral reinnervation, not to a cerebellar or extrapyramidal lesion.
      Curated as an indirect edge because the intermediate is inferred from
      general motor-unit physiology rather than measured in these patients.
- name: Proximal Neurogenic Weakness and Muscle Atrophy
  biological_scale: ORGANISM
  role: consequence
  mechanism_confidence: ESTABLISHED
  description: >-
    The clinical endpoint: proximal and axial weakness with neurogenic muscle
    atrophy, beginning in the lumbar region in the great majority of patients and
    ascending over years. Reflexes are reduced and sensation is preserved, which
    is what separates this from a sensorimotor neuropathy.
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this family, proximal and axial muscle weakness and atrophy, associated
      with abdominal protrusion, defined the motor phenotype.
    explanation: >-
      Describes the motor endpoint of the chain in a VAPB p.Pro56Ser kindred.
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Onset was lumbar in 94%, proximally predominant.
    explanation: >-
      Quantifies the proximal, lumbar-onset distribution across 78 molecularly
      confirmed patients.
  downstream:
  - target: Proximal Muscle Weakness
    causal_link_type: DIRECT
    description: >-
      The clinical expression of this node: proximal, lumbar-predominant
      weakness that ascends over years.
  - target: Camptocormia
    causal_link_type: DIRECT
    description: >-
      Axial extension of the same neurogenic weakness. Failure of the
      paraspinal extensors produces forward flexion of the trunk, and of the
      abdominal wall the abdominal protrusion described in the original
      kindred.
    evidence:
    - reference: PMID:32383641
      reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The clinical features in all patients were camptocormia, fasciculation,
        and weakness in all limbs.
      explanation: >-
        Places camptocormia alongside limb weakness as an expression of the same
        neurogenic process in a p.Pro56Ser family.
  - target: Loss of Ambulation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Cumulative loss of proximal lower-limb and axial motor units over years
    description: >-
      Wheelchair dependence at a median of 7 years from onset is the point at
      which the accumulating proximal deficit crosses a functional threshold,
      not a separate mechanism.
  - target: Respiratory Insufficiency
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Ascending involvement of phrenic and intercostal motor units
    description: >-
      The same ascending neurogenic weakness reaching the respiratory muscles,
      which is why noninvasive ventilation follows loss of ambulation on a
      predictable interval (7 years to wheelchair, 10 to ventilation) and why
      respiratory failure is the terminal event.
- name: Autonomic and Unmyelinated Small-Fibre Degeneration
  biological_scale: TISSUE
  role: consequence
  mechanism_confidence: PROVISIONAL
  description: >-
    A parallel, non-motor arm of the same VAPB deficit: peripheral autonomic and
    other unmyelinated fibres degenerate. Sural nerve biopsy in a p.Pro56Ser
    family showed loss of nerve fibres with a marked unmyelinated-fibre
    predominance and collagen pockets on electron microscopy, and the
    sympathetic skin response was absent. This is curated as a distinct arm
    rather than as part of lower motor neuron degeneration because the affected
    fibres are not motor, and as PROVISIONAL because it rests on two families —
    the original Brazilian kindred and an unrelated Chinese one — rather than on
    the large molecularly confirmed series, which did not assess autonomic
    function.
  evidence:
  - reference: PMID:32383641
    reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sural nerve biopsy revealed loss of nerve fibers, especially unmyelinated
      fibers.
    explanation: >-
      The direct histological observation this node asserts.
  - reference: PMID:32383641
    reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This report indicates that VAPB-associated ALS may be accompanied by
      multifocal autonomic nerve damage.
    explanation: >-
      The authors' own conclusion, and the hedge ("may be") that keeps this node
      at PROVISIONAL confidence.
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autonomic abnormalities were also present, including choking, chronic
      intestinal constipation, sexual dysfunction, and sudomotor abnormalities,
      and on nerve morphology there was involvement of unmyelinated fibers.
    explanation: >-
      Independent replication of unmyelinated-fibre involvement, in the original
      Brazilian kindred rather than the Chinese family.
  downstream:
  - target: Dysautonomia
    causal_link_type: DIRECT
    description: >-
      Loss of peripheral autonomic fibres produces the sudomotor,
      cardiovascular, gastrointestinal and sexual dysfunction recorded as the
      dysautonomia phenotype.
mechanistic_hypotheses:
- hypothesis_group_id: dominant_negative_aggregation
  hypothesis_label: Dominant-negative sequestration of wild-type VAP
  status: CANONICAL
  description: >-
    The historically dominant reading: mutant VAPB misfolds, forms ER-derived
    aggregates, and recruits the wild-type VAPA and VAPB products of the normal
    alleles into those aggregates, so that a heterozygote loses far more VAP
    function than the 50% a null allele would cost. This explains dominance
    without invoking a novel toxic activity, and it is directly demonstrated —
    but in overexpression systems.
  evidence:
  - reference: PMID:17804640
    reference_title: "Motor neuron disease-associated mutant vesicle-associated membrane protein-associated protein (VAP) B recruits wild-type VAPs into endoplasmic reticulum-derived tubular aggregates."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our data support a model in which reduced levels of VAP family proteins
      result in decreased ER anchoring of lipid-binding proteins and cause motor
      neuron degeneration.
    explanation: >-
      States the sequestration model in the authors' own terms.
- hypothesis_group_id: vapb_haploinsufficiency
  hypothesis_label: Haploinsufficiency of the wild-type allele
  status: EMERGING
  description: >-
    The competing reading: at physiological expression a single mutant allele
    produces too little protein to sequester anything, aggregates are not seen in
    patient-derived cells, and what actually matters is that the wild-type allele
    alone cannot supply enough VAPB. On this account the disorder is a
    haploinsufficiency and the aggregates seen in overexpression systems are an
    artefact of dose. The two hypotheses are not mutually exclusive — both
    converge on the same central_effector node — but they imply opposite
    therapeutic strategies (clear the aggregate versus raise wild-type VAPB).
  evidence:
  - reference: PMID:34440634
    reference_title: "The Link between VAPB Loss of Function and Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Instead, loss-of-function of the single wild-type allele is required for
      pathological effects, and VAPB haploinsufficiency may be the main driver of
      the disease.
    explanation: >-
      States the haploinsufficiency hypothesis explicitly.
  - reference: PMID:23446633
    reference_title: "Investigating the contribution of VAPB/ALS8 loss of function in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Thus, Vapb loss of function weakens the motor system of vertebrate animal
      models but is on its own unable to lead to a complete ALS phenotype.
    explanation: >-
      Supports a loss-of-function contribution while showing it is not sufficient
      on its own — which is why this hypothesis is EMERGING rather than
      superseding the dominant-negative account.
phenotypes:
- category: Neurologic
  name: Proximal Muscle Weakness
  description: >-
    The defining clinical feature. Weakness begins proximally, is lumbar in
    origin in the great majority of patients, and ascends over years. Axial
    involvement produces abdominal protrusion and, in some families,
    camptocormia.
  phenotype_term:
    preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
    clinical_course: PROGRESSIVE
    onset:
      onset_category: ADULT
      mean_age_years: 44.9
      notes: >-
        The value in mean_age_years is the cohort MEDIAN (44.9 years,
        PMID:42166520, 78 molecularly confirmed patients); the slot has no
        median field, so it is recorded here and disambiguated in this note,
        following the pattern in CASQ2_CPVT and
        PARK7-Related_Early-Onset_Parkinson_Disease. Do not read it as a mean.
        There was no sex predominance. The generic ADULT bucket (HP:0003581) is
        used rather than MIDDLE_AGE because the series reports only that median,
        not the distribution, so narrowing to a single adult sub-bucket would
        over-specify.
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Median age at onset was 44.9 years; 51% were men.
    explanation: >-
      Establishes adult onset with a median in the fifth decade and no sex bias.
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Onset was lumbar in 94%, proximally predominant.
    explanation: >-
      94% of 78 molecularly confirmed patients had lumbar, proximally predominant
      onset, which maps to VERY_FREQUENT (80-100%).
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this family, proximal and axial muscle weakness and atrophy, associated
      with abdominal protrusion, defined the motor phenotype.
    explanation: >-
      Independent family-level description of the proximal and axial
      distribution.
- category: Neurologic
  name: Proximal Lower Limb Onset Weakness
  description: >-
    The regional axis of the onset, which the unqualified `Proximal Muscle
    Weakness` term does not carry: weakness begins in the proximal legs in the
    large majority of patients and only later ascends to the upper limbs, axial
    muscles and finally the respiratory muscles. Curated as its own phenotype
    because the lumbar onset is the diagnostically useful part — it is what
    separates the presentation from the scapuloperoneal and distal non-5q SMAs
    on the same gene panel — and because it was otherwise recorded only in prose.
  phenotype_term:
    preferred_term: Proximal lower limb muscle weakness
    term:
      id: HP:0008994
      label: Proximal lower limb muscle weakness
    onset:
      onset_category: ADULT
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Onset was lumbar in 94%, proximally predominant.
    explanation: >-
      94% of 78 molecularly confirmed patients maps to VERY_FREQUENT (80-100%),
      and gives both halves of this term at once — lumbar (lower limb) and
      proximal. The deep-research artifact proposed the broader HP:0007340
      (Lower limb muscle weakness); HP:0008994 is preferred because it is the
      term that carries both axes the source states.
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ALS8 is a slowly progressive motor neurone disease with lumbar onset,
      ascending progression, and frequent but subtle UMN signs.
    explanation: >-
      Confirms that the lumbar distribution is the point of onset rather than
      the permanent extent — the deficit ascends — which is why this is curated
      alongside, not instead of, the unqualified proximal weakness phenotype.
- category: Neurologic
  name: Neurogenic Muscle Atrophy
  description: >-
    Muscle wasting secondary to chronic denervation, accompanying the weakness in
    the same proximal and axial distribution.
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this family, proximal and axial muscle weakness and atrophy, associated
      with abdominal protrusion, defined the motor phenotype.
    explanation: >-
      Documents atrophy alongside the weakness.
- category: Neurologic
  name: Fasciculations
  description: >-
    Visible spontaneous motor unit discharges, a cardinal sign of lower motor
    neuron disease and part of the reason this disorder enters the ALS
    differential.
  phenotype_term:
    preferred_term: Fasciculations
    term:
      id: HP:0002380
      label: Fasciculations
  evidence:
  - reference: PMID:32383641
    reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The clinical features in all patients were camptocormia, fasciculation, and
      weakness in all limbs.
    explanation: >-
      Documents fasciculation in every affected member of a p.Pro56Ser family.
- category: Neurologic
  name: Muscle Cramps
  description: >-
    Cramps belong to the lower motor neuron symptom complex here, alongside the
    fasciculations and amyotrophy curated separately. Orphanet names them among
    the cardinal features of this entity. No frequency band is curated because
    no molecularly confirmed p.Pro56Ser series has quantified them — the large
    78-patient cohort reports motor milestones and upper motor neuron signs but
    not cramp burden.
  phenotype_term:
    preferred_term: Muscle cramps
    term:
      id: HP:0003394
      label: Muscle spasm
  evidence:
  - reference: ORPHA:209335
    reference_title: "Autosomal dominant adult-onset proximal spinal muscular atrophy"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      A rare, genetic, motor neuron disease characterized by adulthood-onset of
      slowly progressive, proximal muscular weakness with fasciculations,
      amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or
      pyramidal involvement.
    explanation: >-
      The Orphanet definition of this entity names cramps among its cardinal
      features. Note that this entry records a REFUTE elsewhere against the same
      sentence, but that disagreement is confined to the clause excluding
      pyramidal and bulbar involvement; the cramps clause is not in dispute and
      is corroborated by the wider ALS8 literature.
- category: Neurologic
  name: Camptocormia
  description: >-
    Forward flexion of the trunk from axial (paraspinal) weakness. Reported as a
    uniform feature of the Chinese p.Pro56Ser kindred and the same axial
    involvement that produces abdominal protrusion in the Brazilian families.
  phenotype_term:
    preferred_term: Camptocormia
    term:
      id: HP:0100595
      label: Camptocormia
  evidence:
  - reference: PMID:32383641
    reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The clinical features in all patients were camptocormia, fasciculation, and
      weakness in all limbs.
    explanation: >-
      Documents camptocormia in all affected members of this family.
- category: Neurologic
  name: Reduced Tendon Reflexes
  description: >-
    Hyporeflexia with reduced tone, the expected examination finding when the
    lesion is at the anterior horn cell and no upper motor neuron signs are
    present. Note that this is the Finkel-end finding; pyramidal signs are
    frequent across the wider ALS8 spectrum.
  phenotype_term:
    preferred_term: Reduced tendon reflexes
    term:
      id: HP:0001315
      label: Reduced tendon reflexes
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Tone and tendon reflexes were decreased and a distal tremor was common.
    explanation: >-
      Documents decreased tone and reflexes in the affected kindred.
- category: Neurologic
  name: Distal Tremor
  description: >-
    A distal tremor, common in the affected kindred and a recognised
    accompaniment of chronic partial denervation with enlarged motor units. The
    deep-research artifact proposed postural tremor here; the cited source says
    only "distal tremor", so the generic HP:0001337 Tremor is retained rather
    than asserting a postural qualifier no cited abstract supports.
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  frequency: FREQUENT
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Tone and tendon reflexes were decreased and a distal tremor was common.
    explanation: >-
      "Common" maps to FREQUENT (30-79%) under the GeneReviews prose-to-enum
      convention; no numerator was reported.
- category: Neurologic
  name: Abnormal Pyramidal Signs
  description: >-
    The boundary phenotype. Subtle upper motor neuron signs were present in 53 of
    78 molecularly confirmed p.Pro56Ser patients, and 30% of those presenting as
    pure progressive muscular atrophy later developed them — no patient had
    clonus. This is curated because it is the empirical reason the Finkel-type
    SMA label and the ALS8 label do not partition the same allele cleanly, not
    because pyramidal signs belong to the pure SMA phenotype.
  phenotype_term:
    preferred_term: Abnormal pyramidal sign
    term:
      id: HP:0007256
      label: Abnormal pyramidal sign
  frequency: FREQUENT
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      UMN signs were present in 53 patients; none exhibited clonus.
    explanation: >-
      53 of 78 patients is 68%, which maps to FREQUENT (30-79%).
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At admission, 51% had spinal-onset ALS, 42% progressive muscular atrophy
      (PMA) and 6% flail leg; 30% of patients with PMA subsequently developed UMN
      signs.
    explanation: >-
      Shows the pure lower motor neuron presentation is a large minority that
      partially converts, which is the phenotypic-boundary problem this entry
      records.
  - reference: ORPHA:209335
    reference_title: "Autosomal dominant adult-onset proximal spinal muscular atrophy"
    supports: REFUTE
    evidence_source: OTHER
    snippet: >-
      A rare, genetic, motor neuron disease characterized by adulthood-onset of
      slowly progressive, proximal muscular weakness with fasciculations,
      amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or
      pyramidal involvement.
    explanation: >-
      Orphanet defines this entity as excluding pyramidal involvement, so by that
      definition the phenotype curated here does not belong to it. This is a
      nosological stance rather than a contrary observation — Orphanet is drawing
      the SMA/ALS8 boundary at the absence of upper motor neuron signs, while the
      molecularly confirmed series finds those signs in 53 of 78 p.Pro56Ser
      carriers. Recorded as REFUTE so the disagreement between the definition and
      the cohort is visible rather than silently resolved in favour of one.
- category: Autonomic
  name: Dysautonomia
  description: >-
    Autonomic involvement — choking, constipation, sexual dysfunction, sudomotor
    abnormalities, orthostatic hypotension — with loss of unmyelinated fibres on
    nerve morphology. This is curated as a real but non-obligate feature of the
    p.Pro56Ser phenotype rather than as a defining one: the authors of the
    Brazilian kindred proposed that motor-plus-autonomic involvement constitutes
    a separate category of disease, and it was subsequently replicated in an
    unrelated Chinese family. It is not reported in most Finkel-type
    descriptions.
  phenotype_term:
    preferred_term: Orthostatic hypotension due to autonomic dysfunction
    term:
      id: HP:0004926
      label: Orthostatic hypotension due to autonomic dysfunction
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autonomic abnormalities were also present, including choking, chronic
      intestinal constipation, sexual dysfunction, and sudomotor abnormalities,
      and on nerve morphology there was involvement of unmyelinated fibers.
    explanation: >-
      Documents the autonomic syndrome and its unmyelinated-fibre substrate.
  - reference: PMID:32383641
    reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two patients developed symptoms of dysautonomia, including abdominal
      bloating, orthostatic hypotension, constipation, frequent urination,
      decreased sweating, and burning feet.
    explanation: >-
      Independent replication in an unrelated family, including the orthostatic
      hypotension this phenotype term names.
  sequelae:
  - target: Constipation
    causal_link_type: DIRECT
    description: >-
      Constipation is curated as its own phenotype because it is the autonomic
      feature patients report most, but mechanistically it is one manifestation
      of the dysautonomia node rather than an independent process.
    evidence:
    - reference: PMID:32383641
      reference_title: "Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Two patients developed symptoms of dysautonomia, including abdominal
        bloating, orthostatic hypotension, constipation, frequent urination,
        decreased sweating, and burning feet.
      explanation: >-
        Lists constipation as a component of the dysautonomia syndrome, which is
        the claim this edge makes.
- category: Gastrointestinal
  name: Constipation
  description: >-
    Chronic intestinal constipation as part of the autonomic involvement.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
    temporality: CHRONIC
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autonomic abnormalities were also present, including choking, chronic
      intestinal constipation, sexual dysfunction, and sudomotor abnormalities,
      and on nerve morphology there was involvement of unmyelinated fibers.
    explanation: >-
      Names chronic intestinal constipation among the autonomic features.
- category: Respiratory
  name: Respiratory Insufficiency
  description: >-
    Respiratory muscle involvement is the principal cause of death and the
    milestone that most shapes management. Median time from onset to
    noninvasive ventilation is 10 years across the ALS8 series; in the
    dysautonomic Brazilian kindred death occurred in 10-15 years from
    respiratory insufficiency.
  phenotype_term:
    preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Death occurred in 10-15 years due to respiratory insufficiency.
    explanation: >-
      Identifies respiratory failure as the terminal event in this kindred.
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Survival was 21.9 years; times to wheelchair dependence and noninvasive
      ventilation were 7.0 and 10.0 years, respectively.
    explanation: >-
      Quantifies the ventilation milestone across the largest reported series.
- category: Neurologic
  name: Bulbar Involvement
  description: >-
    Bulbar features occur in about a fifth of ALS8 patients and are predominantly
    dysphonia rather than the dysarthria-dysphagia pattern of bulbar-onset ALS.
    Not an early or defining feature of the Finkel-type presentation.
  phenotype_term:
    preferred_term: Dysphonia
    term:
      id: HP:0001618
      label: Dysphonia
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Bulbar involvement occurred in 17 (21.8%) patients, predominantly as
      dysphonia.
    explanation: >-
      21.8% maps to OCCASIONAL (5-29%), and the paper names dysphonia as the
      predominant form.
  - reference: ORPHA:209335
    reference_title: "Autosomal dominant adult-onset proximal spinal muscular atrophy"
    supports: REFUTE
    evidence_source: OTHER
    snippet: >-
      A rare, genetic, motor neuron disease characterized by adulthood-onset of
      slowly progressive, proximal muscular weakness with fasciculations,
      amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or
      pyramidal involvement.
    explanation: >-
      Orphanet's definition of this entity excludes bulbar involvement, which the
      21.8% figure from the molecularly confirmed series contradicts. Curated as
      REFUTE for the same reason as the pyramidal-signs node: the disagreement is
      between a nosological definition and a genotype-defined cohort, and is the
      substance of this entry's scope problem.
- category: Neurologic
  name: Loss of Ambulation
  description: >-
    Wheelchair dependence is reached at a median of 7 years from onset — early
    relative to the 21.9-year median survival, so most patients live many years
    with substantial motor disability rather than dying soon after losing
    ambulation.
  phenotype_term:
    preferred_term: Loss of ambulation
    term:
      id: HP:0002505
      label: Loss of ambulation
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Survival was 21.9 years; times to wheelchair dependence and noninvasive
      ventilation were 7.0 and 10.0 years, respectively.
    explanation: >-
      Gives the median time to wheelchair dependence.
genetic:
- name: VAPB
  gene_term:
    preferred_term: VAPB
    term:
      id: hgnc:12649
      label: VAPB
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: PRESENT
  notes: >-
    VAPB (20q13.32) encodes VAMP-associated protein B/C, a type II integral
    membrane protein of the endoplasmic reticulum whose cytosolic MSP domain
    recruits FFAT-motif partners and so builds membrane contact sites between the
    ER and essentially every other cellular membrane. The recurrent disease
    allele is c.166C>T (p.Pro56Ser), which lies in the MSP domain.

    Two facts about this gene shape how a VAPB result should be read. First,
    p.Pro56Ser is not a set of independent observations: haplotype analysis of
    eight families of both Portuguese-Brazilian and African-Brazilian ancestry
    traces them all to one founding event about 23 generations ago, so the
    apparent recurrence of the allele is largely genealogy. Second, one allele
    does not equal one phenotype — the same p.Pro56Ser produces late-onset SMA,
    slowly progressive atypical ALS, and rapidly progressive typical ALS in
    different kindreds, and no modifier explaining that has been identified.

    Other VAPB variants (T46I, A145V, S160del) have been reported in ALS
    cohorts, but the Finkel-type SMA phenotype curated here is a p.Pro56Ser
    phenotype; nothing establishes that the other alleles produce it.
  evidence:
  - reference: PMID:15372378
    reference_title: "A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequently, the same mutation was identified in patients from six
      additional kindreds but with different clinical courses, such as ALS8,
      late-onset SMA, and typical severe ALS with rapid progression.
    explanation: >-
      Establishes gene-disease causation and, in the same sentence, the
      one-allele-many-phenotypes problem.
  - reference: PMID:16187141
    reference_title: "A common founder for amyotrophic lateral sclerosis type 8 (ALS8) in the Brazilian population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Eight families, comprising more than 1,500 individuals of whom about 200 are
      affected, are now known to carry this mutation.
    explanation: >-
      Gives the size of the known p.Pro56Ser population and its family structure.
  - reference: PMID:34440634
    reference_title: "The Link between VAPB Loss of Function and Amyotrophic Lateral Sclerosis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The VAP proteins are integral adaptor proteins of the endoplasmic reticulum
      (ER) membrane that recruit a myriad of interacting partners to the ER
      surface.
    explanation: >-
      States the normal molecular function of the affected protein.
  - reference: PMID:23446633
    reference_title: "Investigating the contribution of VAPB/ALS8 loss of function in amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In order to identify additional ALS-associated VAPB mutations, we screened
      the entire VAPB gene in a cohort of ALS patients and detected two mutations
      (A145V and S160Δ).
    explanation: >-
      Documents the additional VAPB alleles found in ALS cohorts, which are not
      the Finkel-type allele.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population-based prevalence or incidence estimate exists. The largest
    enumeration is of the founder p.Pro56Ser population: eight families totalling
    more than 1,500 individuals of whom about 200 were affected, with a later
    clinical series assembling 78 molecularly confirmed patients from 57
    apparently unrelated families. These are pedigree counts, heavily enriched
    for Brazilian families of Portuguese ancestry, and cannot be converted into a
    population rate.
  evidence:
  - reference: PMID:16187141
    reference_title: "A common founder for amyotrophic lateral sclerosis type 8 (ALS8) in the Brazilian population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Eight families, comprising more than 1,500 individuals of whom about 200 are
      affected, are now known to carry this mutation.
    explanation: >-
      The affected-case enumeration behind the CASES_IN_LITERATURE measure.
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We retrospectively analyzed 78 patients with ALS8 confirmed via molecular
      testing or familial linkage analysis from 57 apparently unrelated families.
    explanation: >-
      The largest molecularly confirmed series, again a case count rather than a
      rate.
progression:
- phase: Slowly progressive ascending course
  age_range: onset in the fifth decade
  notes: >-
    Onset is insidious in the fifth decade, lumbar and proximal. Weakness
    ascends; wheelchair dependence follows at a median of 7 years and
    noninvasive ventilation at 10 years, but median survival is 21.9 years — an
    order of magnitude longer than typical ALS. Mortality is nonetheless
    elevated, with a standardized mortality ratio of 4.54. Upper motor neuron
    status does not affect survival.
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ALS8 is a slowly progressive motor neurone disease with lumbar onset,
      ascending progression, and frequent but subtle UMN signs.
    explanation: >-
      The authors' own summary of the course.
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      UMN status did not affect survival (p = 0.312). The standardized mortality
      ratio was 4.54 (95% CI 2.77-7.01), supporting disease-related excess
      mortality.
    explanation: >-
      Quantifies excess mortality and shows the UMN/LMN split is not
      prognostically separating.
treatments:
- name: Noninvasive Ventilation
  description: >-
    Ventilatory support, typically bilevel positive airway pressure, once
    respiratory muscle weakness produces orthostatic breathlessness, orthopnoea
    or nocturnal hypoventilation. This is the single most consequential
    supportive intervention in this disorder because respiratory insufficiency
    is the terminal event, and because the natural history is slow and
    predictable enough to anticipate: the molecularly confirmed p.Pro56Ser
    series places the median time from onset to noninvasive ventilation at 10
    years, three years after wheelchair dependence. It is not disease-modifying
    — see the vapb_no_disease_modifying_therapy discussion — and it does not
    slow denervation.
  action_category: THERAPEUTIC
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: noninvasive ventilation
    term:
      id: NCIT:C171457
      label: Non-Invasive Mechanical Ventilation
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Survival was 21.9 years; times to wheelchair dependence and noninvasive
      ventilation were 7.0 and 10.0 years, respectively.
    explanation: >-
      Establishes noninvasive ventilation as a milestone actually reached by
      this p.Pro56Ser cohort, and dates it, which is what makes it curatable
      here rather than merely plausible by analogy with ALS.
  - 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: >-
      Expert-panel respiratory-care guidance for motor neurone disease naming
      NIV as the main recognized treatment for the respiratory failure this
      disorder ends in. PARTIAL, not SUPPORT, on the same ground as the Bourke
      trial below: the guidance is written for ALS, not for VAPB p.Pro56Ser
      carriers. ALS8 sits inside that clinical category and 51% of the
      p.Pro56Ser series presented as spinal-onset ALS, but that is an
      extrapolation and is tagged as one.
  - 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
    evidence_source: HUMAN_CLINICAL
    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: >-
      The controlled evidence that NIV extends survival and preserves quality of
      life in motor neurone disease. Marked PARTIAL rather than SUPPORT because
      the trial was in ALS, not in VAPB p.Pro56Ser carriers, and its benefit was
      confined to the subgroup with better bulbar function — no NIV trial has
      been run in this disorder, and none is likely at this prevalence.
  target_mechanisms:
  - target: Respiratory Insufficiency
    treatment_effect: BYPASSES
    description: >-
      NIV supplies mechanically the inspiratory pressure that denervated
      diaphragmatic and intercostal motor units can no longer generate. It works
      around the failing effector rather than acting anywhere on the upstream
      VAPB chain, which is why the effect is BYPASSES and why it is compatible
      with continued progression of the mechanism it compensates for.
    evidence:
    - reference: PMID:42166520
      reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Survival was 21.9 years; times to wheelchair dependence and noninvasive
        ventilation were 7.0 and 10.0 years, respectively.
      explanation: >-
        Ties the intervention to this disorder's respiratory endpoint on a dated
        milestone rather than a general indication.
- name: Physical Therapy and Rehabilitation
  description: >-
    Stage-matched rehabilitation — range-of-motion work, gait and transfer
    training, orthoses, mobility aids and eventually wheelchair provision —
    aimed at independence, safety and prevention of secondary complications such
    as contractures and falls. The unusually long course here makes this weigh
    more than it does in typical ALS: median survival is 21.9 years while
    wheelchair dependence arrives at 7, so most patients live over a decade with
    substantial motor disability.
  action_category: THERAPEUTIC
  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
    evidence_source: HUMAN_CLINICAL
    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: >-
      States the goal and scope of rehabilitation in progressive motor neurone
      disease. PARTIAL because it is a narrative review addressed to ALS, with
      no VAPB-specific rehabilitation study to cite; the stage-matched principle
      transfers, the effect size is not established for this disorder.
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Survival was 21.9 years; times to wheelchair dependence and noninvasive
      ventilation were 7.0 and 10.0 years, respectively.
    explanation: >-
      The gap between wheelchair dependence at 7 years and death at 21.9 is the
      disease-specific reason rehabilitation matters here — it quantifies the
      long period of survival with disability that rehabilitation is addressed
      to.
  target_mechanisms:
  - target: Loss of Ambulation
    treatment_effect: MODULATES
    description: >-
      Rehabilitation acts on the functional consequence, not on the denervation
      producing it: gait training, orthoses and mobility aids alter how much
      disability a given degree of proximal weakness imposes and when the
      wheelchair threshold is crossed. MODULATES rather than INHIBITS because no
      evidence shows rehabilitation slows motor unit loss.
    evidence:
    - reference: PMID:24510737
      reference_title: "Rehabilitation in amyotrophic lateral sclerosis: why it matters."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Given the progressive nature of ALS, the clinician must be aware of the
        expected disease trajectory and apply appropriate interventions at each
        stage.
      explanation: >-
        The stage-matched principle that connects the intervention to the
        ambulation milestone. PARTIAL for the same ALS-versus-ALS8 reason as
        above.
- name: Genetic Counseling
  description: >-
    Counselling for an autosomal dominant, adult-onset, fully penetrant-appearing
    founder allele, where at-risk relatives are typically adults who have already
    reproduced. The 78-patient natural-history series explicitly frames its own
    findings as supporting genetic counselling and anticipatory management, which
    is the practical output of characterizing a course this predictable.
  action_category: COUNSELING_INFORMATIONAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These findings expand the phenotypic characterization of ALS8 and support
      genetic counseling and anticipatory management.
    explanation: >-
      The authors' own statement of what the natural-history data are for. No
      target_mechanisms is set because counselling is a non-therapeutic action
      and does not act on a pathograph node.

diagnosis:
- name: Electromyography showing chronic denervation and reinnervation
  description: >-
    Needle EMG establishes an anterior-horn-cell process: ongoing denervation
    with reinnervation, large motor unit potentials and reduced recruitment, with
    preserved sensory responses. This is what separates the disorder from a
    sensorimotor polyneuropathy and, together with the family history, what
    prompts genetic testing.
  evidence:
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Electromyography disclosed ongoing denervation and reinnervation.
    explanation: >-
      The characteristic electrodiagnostic finding.
  - reference: PMID:16967488
    reference_title: "Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Tone and tendon reflexes were decreased and a distal tremor was common.
      Sensation was preserved.
    explanation: >-
      Records the lower-motor-neuron exam with preserved sensation, which keeps
      the diagnosis in the motor neuronopathy column rather than a sensorimotor
      polyneuropathy.
- name: Molecular testing for VAPB in non-5q spinal muscular atrophy
  description: >-
    After SMN1 deletion has been excluded, VAPB is one of the genes on the
    non-5q SMA / hereditary motor neuropathy panel. Diagnostic yield in this
    group is modest and lowest in exactly the presentation this disorder
    produces — pure proximal weakness — so a negative panel does not close the
    question.
  evidence:
  - reference: PMID:37470033
    reference_title: "Phenotype Presentation and Molecular Diagnostic Yield in Non-5q Spinal Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The genetic diagnostic yield was lowest in P-SMA (6/21, 28.6%) compared with
      PD-SMA (16/35, 45.7%) and SP-SMA (10/15, 66.7%).
    explanation: >-
      Quantifies the diagnostic difficulty of the pure proximal non-5q SMA
      presentation.
  - reference: PMID:37470033
    reference_title: "Phenotype Presentation and Molecular Diagnostic Yield in Non-5q Spinal Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Non-5q SMA is genetically heterogeneous, and neuropathy gene panels achieve
      a molecular diagnosis in one-third of the patients.
    explanation: >-
      States the overall panel yield in the differential category this disorder
      belongs to.
differential_diagnoses:
- name: 5q spinal muscular atrophy (SMN1-related)
  description: >-
    The disease the name most invites confusion with, and mechanistically
    unrelated: 5q SMA is autosomal recessive, caused by homozygous SMN1
    deletion, and modified by SMN2 copy number. It is also the one with approved
    SMN-directed therapies. Excluding the SMN1 deletion is the first step in
    evaluating an adult proximal SMA phenotype.
  evidence:
  - reference: PMID:37470033
    reference_title: "Phenotype Presentation and Molecular Diagnostic Yield in Non-5q Spinal Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Spinal muscular atrophy (SMA) is mainly caused by homozygous SMN1 gene
      deletions on 5q13.
    explanation: >-
      States the genetic basis of the disorder that must be excluded first.
- name: Amyotrophic lateral sclerosis
  description: >-
    Not a clean differential so much as a continuum: the same VAPB p.Pro56Ser
    allele produces late-onset SMA, atypical slowly progressive ALS, and
    rapidly progressive typical ALS in different kindreds, and most ALS8 patients
    eventually show subtle pyramidal signs. Distinguishing them matters
    prognostically — median survival here is 21.9 years — but the boundary is
    clinical, not molecular.
  evidence:
  - reference: PMID:15372378
    reference_title: "A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subsequently, the same mutation was identified in patients from six
      additional kindreds but with different clinical courses, such as ALS8,
      late-onset SMA, and typical severe ALS with rapid progression.
    explanation: >-
      Establishes that SMA and ALS presentations share the identical allele.
- name: Other non-5q spinal muscular atrophies and hereditary motor neuropathies
  description: >-
    BICD2, DYNC1H1, TRPV4, VCP, HSPB1, VRK1, DNAJB2, MORC2, ASAH1, HEXB and the
    androgen receptor (Kennedy disease) all produce adult proximal or
    proximal-distal motor neuronopathy phenotypes. In a French/UK series of 71
    non-5q SMA patients, BICD2 and DYNC1H1 were the commonest causes found.
  evidence:
  - reference: PMID:37470033
    reference_title: "Phenotype Presentation and Molecular Diagnostic Yield in Non-5q Spinal Muscular Atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thirty-two patients (45.1%) had a genetic diagnosis: BICD2 (n = 9), DYNC1H1
      (n = 7), TRPV4 (n = 4), VCP, HSBP1, AR (n = 2), VRK1, DNAJB2, MORC2, ASAH1,
      HEXB, and unexpectedly, COL6A3 (n = 1).
    explanation: >-
      Enumerates the genes competing for this clinical phenotype.
animal_models:
- name: Vapb P56S knock-in mouse
  species: Mouse
  genotype: Vapb p.Pro56Ser knock-in (heterozygous and homozygous)
  publication: PMID:26362257
  description: >-
    The most physiologic rodent model: the endogenous Vapb locus carries the
    P56S change, so expression level and tissue distribution are normal.
    Heterozygotes — the human genotype — show mild age-dependent motor deficits;
    homozygotes are worse, giving a dose-response consistent with the dominant
    human allele.
  modeled_mechanisms:
  - target: ER Stress and Unfolded Protein Response Activation
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      ER stress and an autophagic response appear in motor neurons before
      behavioural deficits, at physiological expression level.
    limitations: >-
      The behavioural phenotype is mild and late; the model does not reproduce
      the severe weakness or the respiratory failure that ends the human disease,
      so it informs the initiating steps rather than the clinical endpoint.
    readouts:
    - name: ER stress markers in motor neurons
      target: ER Stress and Unfolded Protein Response Activation
      direction: INCREASED
      interpretation: >-
        Induction of ER stress precedes overt motor behavioural defects,
        positioning this node upstream in the chain.
      evidence:
      - reference: PMID:26362257
        reference_title: "Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          The mutant mice demonstrate induction of ER stress and autophagic
          response in motor neurons before obvious onset of behavioral defects,
          suggesting that these cellular biological defects might contribute to
          the initiation of the disease.
        explanation: >-
          The measurement behind this readout and its temporal ordering.
    evidence:
    - reference: PMID:26362257
      reference_title: "Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Heterozygous P56S Vapb knock-in mice show mild age-dependent defects in
        motor behaviors as characteristic features of the disease.
      explanation: >-
        Supports treating the heterozygous knock-in as informative for the human
        heterozygous disease.
  - target: ER-Derived Aggregation of Misfolded VAPB
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Cytoplasmic inclusions containing P56S VAPB and ubiquitinated protein form
      selectively in motor neurons at physiological expression level — the
      counter-observation to the claim that aggregates are purely an
      overexpression artefact.
    limitations: >-
      Aggregation in mouse motor neurons does not settle whether aggregates form
      in human motor neurons, where the observation has not been made.
    evidence:
    - reference: PMID:26362257
      reference_title: "Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Significantly, the knock-in mice demonstrate accumulation of P56S VAPB
        protein and ubiquitinated proteins in cytoplasmic inclusions, selectively
        in motor neurons.
      explanation: >-
        Documents aggregation without overexpression.
- name: Thy1.2 P56S VAPB transgenic mouse
  species: Mouse
  genotype: Thy1.2-driven pan-neuronal human VAPB p.Pro56Ser transgene
  publication: PMID:23771029
  description: >-
    Pan-neuronal overexpression of human P56S VAPB. Instructive precisely
    because its cell-type selectivity is the opposite of the human Finkel
    phenotype: corticospinal motor neurons are progressively lost while spinal
    motor neurons survive with functional impairment.
  modeled_mechanisms:
  - target: Lower Motor Neuron Degeneration
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      Spinal motor neurons show altered C-bouton morphology and impaired
      spontaneous rhythmic discharge, but do not die; the population that dies is
      the corticospinal one.
    limitations: >-
      The human disorder curated here is defined by lower motor neuron loss with
      no upper motor neuron signs. This model inverts that, and its transgene is
      overexpressed under a heterologous promoter, so it cannot be used to argue
      about which motor neuron population is vulnerable in patients.
    readouts:
    - name: Spinal motor neuron survival
      target: Lower Motor Neuron Degeneration
      direction: UNCHANGED
      interpretation: >-
        A negative result: spinal motor neuron number was preserved despite
        progressive corticospinal loss.
      evidence:
      - reference: PMID:23771029
        reference_title: "Amyotrophic lateral sclerosis-related VAPB P56S mutation differentially affects the function and survival of corticospinal and spinal motor neurons."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          However, only a progressive loss of CSMNs but not SMNs was found in P56S
          VAPB Tg mice.
        explanation: >-
          The survival measurement behind this readout.
    evidence:
    - reference: PMID:23771029
      reference_title: "Amyotrophic lateral sclerosis-related VAPB P56S mutation differentially affects the function and survival of corticospinal and spinal motor neurons."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        While WT VAPB Tg mice did not exhibit any overt motor behavioral
        phenotypes, P56S VAPB Tg mice developed progressive hyperactivities and
        other motor abnormalities.
      explanation: >-
        Establishes an allele-specific motor phenotype while the accompanying
        limitation records why its cell-type pattern does not match the human
        disorder.
- name: Vapb knockout mouse
  species: Mouse
  genotype: Vapb null (complete loss of Vapb expression)
  publication: PMID:23446633
  description: >-
    A direct test of the haploinsufficiency hypothesis: if losing VAPB function
    were sufficient, a null mouse should develop motor neuron disease. It largely
    does not.
  modeled_mechanisms:
  - target: Lower Motor Neuron Degeneration
    relationship: FAILS_TO_RECAPITULATE
    fidelity: MODERATE
    description: >-
      Complete loss of Vapb produced only mild motor deficits after 18 months and
      left neuromuscular junctions innervated — no motor neuron disease.
    limitations: >-
      This is a null, not the human heterozygous missense genotype, and mouse
      lifespan may be too short for a disorder with a 45-year human onset. It
      therefore constrains rather than refutes the loss-of-function hypothesis:
      loss of VAPB function alone is insufficient in mouse, which is compatible
      with it being necessary but requiring the additional dominant-negative
      component.
    evidence:
    - reference: PMID:23446633
      reference_title: "Investigating the contribution of VAPB/ALS8 loss of function in amyotrophic lateral sclerosis."
      supports: REFUTE
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Mice knocked-out for Vapb showed mild motor deficits after 18 months of age
        yet had innervated neuromuscular junctions (NMJs).
      explanation: >-
        The negative result: complete VAPB loss does not reproduce motor neuron
        degeneration or denervation in mouse.
experimental_models:
- name: ALS8 patient-derived iPSC motor neurons
  experimental_model_type: IPSC_DERIVED_MODEL
  description: >-
    Fibroblasts from p.Pro56Ser patients and their non-carrier siblings
    reprogrammed to iPSC and differentiated into motor neurons — the closest
    available human-cell model, with sibling controls.
  publication: PMID:21685205
  modeled_mechanisms:
  - target: Loss of Functional VAPB at ER Membrane Contact Sites
    relationship: MEASURES
    fidelity: HIGH
    description: >-
      VAPB protein is reduced in patient-derived motor neurons relative to
      non-carrier siblings, at endogenous expression levels.
    limitations: >-
      iPSC-derived motor neurons are developmentally immature and cannot model a
      disorder whose onset is in the fifth decade; the reduction is a molecular
      readout, not a degeneration phenotype.
    readouts:
    - name: VAPB protein level in patient motor neurons
      target: Loss of Functional VAPB at ER Membrane Contact Sites
      direction: DECREASED
      interpretation: >-
        Reduced VAPB in human patient motor neurons, supporting a functional
        shortfall of the protein as the convergent effector.
      evidence:
      - reference: PMID:21685205
        reference_title: "Downregulation of VAPB expression in motor neurons derived from induced pluripotent stem cells of ALS8 patients."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          We show for the first time that VAPB protein levels are reduced in
          ALS8-derived motor neurons but, in contrast to over-expression systems,
          cytoplasmic aggregates could not be identified.
        explanation: >-
          The measurement behind this readout, and its explicit contrast with
          overexpression systems.
discussions:
- discussion_id: vapb_p56s_one_allele_many_phenotypes
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why does a single founder allele, VAPB p.Pro56Ser, produce late-onset Finkel
    SMA in some carriers, slowly progressive atypical ALS in others, and rapidly
    progressive typical ALS in a few?
  attaches_to:
  - "pathophysiology#VAPB p.Pro56Ser MSP-Domain Variant"
  - "pathophysiology#Lower Motor Neuron Degeneration"
  rationale: >-
    This is the central unresolved question for this entry, and it is unusually
    well posed because the founder effect removes allelic heterogeneity as an
    explanation: nearly all reported patients carry the same ancestral
    chromosome. The 2004 discovery paper already reported the three courses
    across seven kindreds, and the 2026 series of 78 patients quantified the
    split — 42% presenting as pure progressive muscular atrophy, of whom 30%
    later developed upper motor neuron signs. Whatever separates them is
    therefore modifier, environmental or stochastic, and none has been
    identified. Practically, this determines whether MONDO:0008453 names a
    disease or a presentation.
  evidence:
  - reference: PMID:42166520
    reference_title: "Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At admission, 51% had spinal-onset ALS, 42% progressive muscular atrophy
      (PMA) and 6% flail leg; 30% of patients with PMA subsequently developed UMN
      signs.
    explanation: >-
      Quantifies the phenotypic split within one allele and the partial
      conversion between categories over time.
  - reference: ORPHA:209335
    reference_title: "Autosomal dominant adult-onset proximal spinal muscular atrophy"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      A rare, genetic, motor neuron disease characterized by adulthood-onset of
      slowly progressive, proximal muscular weakness with fasciculations,
      amyotrophy, cramps, and absent/hypoactive reflexes, without bulbar or
      pyramidal involvement.
    explanation: >-
      Supplies the other half of the problem. Orphanet keeps this entity distinct
      from ALS8 by defining it as free of bulbar and pyramidal involvement, but
      the allele that causes it produces both in most carriers. The gap between
      the reference nosology and the molecular cohort is what makes it unclear
      whether MONDO:0008453 names a disease or a presentation.
  - reference: PMID:34133501
    reference_title: "The history behind ALS type 8: from the first phenotype description to the discovery of VAPB mutation."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Over the past 68 years, the Finkel type late-onset adult autosomal dominant
      spinal muscular atrophy (SMA) that is allelic with amyotrophic lateral
      sclerosis-8 (ALS8) gained a genotype-phenotype correlation among the motor
      neuron diseases through the work of groups led by Zatz and Marques Jr.
    explanation: >-
      States the allelism directly: Finkel-type SMA and ALS8 are the same locus,
      which is the premise of this discussion. The open question is not whether
      the two labels share an allele but why the shared allele produces both.
      Tagged OTHER because it is a historical review, not a study contributing
      observations.
  proposed_experiments:
  - experiment_id: exp_vapb_modifier_scan_within_founder_pedigree
    name: Genome-wide modifier scan within the founder pedigree
    description: >-
      Because carriers share one ancestral haplotype, a within-pedigree
      association of genome-wide genotype against presentation category (pure
      LMN versus UMN-positive) and age at onset isolates modifiers with the
      causal allele held constant — a design most Mendelian disorders cannot
      support.
  - experiment_id: exp_vapb_isogenic_motor_neuron_subtype_panel
    name: Isogenic corticospinal versus spinal motor neuron comparison
    description: >-
      Introduce p.Pro56Ser into isogenic iPSC lines differentiated separately to
      corticospinal-like and spinal motor neurons, and compare ER stress,
      contact-site integrity and survival, testing whether the corticospinal
      selectivity seen in the transgenic mouse is a property of the neuron
      subtype or of the transgene.
- discussion_id: vapb_aggregates_absent_at_physiological_expression
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Do the ER-derived VAPB aggregates that dominate the mechanistic literature
    actually form in human motor neurons carrying one p.Pro56Ser allele, or are
    they an artefact of overexpression?
  attaches_to:
  - "pathophysiology#ER-Derived Aggregation of Misfolded VAPB"
  rationale: >-
    The aggregation-and-sequestration model was built almost entirely in
    overexpression systems, where mutant VAPB reliably forms tubular ER clusters
    and drags in wild-type VAP. Three lines of evidence complicate transferring
    that to patients. Patient-derived iPSC motor neurons show reduced VAPB but no
    identifiable cytoplasmic aggregates. In transgenic mice the inclusions do not
    correlate with degeneration, disappear after axotomy, and behave as a
    reversible ERAD-linked quality-control compartment — possibly protective.
    Against that, physiological-level knock-in mice do form motor-neuron
    inclusions, so dose alone does not explain the discrepancy. The mismatch is
    not academic: it decides whether a therapy should clear aggregates or restore
    wild-type VAPB, and the two hypotheses in mechanistic_hypotheses point in
    opposite directions.
  evidence:
  - reference: PMID:21685205
    reference_title: "Downregulation of VAPB expression in motor neurons derived from induced pluripotent stem cells of ALS8 patients."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our results suggest that optimal levels of VAPB may play a central role in
      the pathogenesis of ALS8, in agreement with the observed reduction of VAPB
      in sporadic ALS.
    explanation: >-
      The patient-cell result reframing the mechanism around VAPB levels rather
      than aggregates.
  - reference: PMID:24252306
    reference_title: "Amyotrophic lateral sclerosis (ALS)-associated VAPB-P56S inclusions represent an ER quality control compartment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The presence of these inclusions does not correlate with signs of axonal and
      neuronal degeneration, and axotomy leads to their gradual disappearance,
      indicating that they represent reversible structures.
    explanation: >-
      Uncouples inclusion burden from degeneration in the model where the
      inclusions are most conspicuous.
  proposed_experiments:
  - experiment_id: exp_vapb_aggregate_detection_in_patient_tissue
    name: Aggregate detection in ALS8 patient spinal cord
    description: >-
      Examine post-mortem anterior horn tissue from p.Pro56Ser patients for
      ER-derived VAPB inclusions and for wild-type VAPA/VAPB redistribution,
      against age-matched controls. This is the observation the whole
      dominant-negative model rests on and it has not been reported in human
      motor neurons.
- discussion_id: vapb_no_disease_modifying_therapy
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is there any disease-modifying treatment for VAPB-related SMA, and does the
    SMN-directed therapeutic success in 5q SMA transfer?
  attaches_to:
  - "pathophysiology#Loss of Functional VAPB at ER Membrane Contact Sites"
  rationale: >-
    Every treatment curated in this entry is supportive: rehabilitation,
    mobility aids, noninvasive ventilation, genetic counselling. None of it is
    disease-modifying, and nothing in `treatments` should be read as implying
    otherwise — the `target_mechanisms` links land on the downstream
    manifestations (`Respiratory Insufficiency`, `Loss of Ambulation`) and
    nowhere on the VAPB chain that produces them. Nutritional and swallowing
    support belong in the same category but are not curated for want of a
    disorder-specific citation. The specific hazard worth naming is the shared
    "spinal muscular atrophy" label: nusinersen,
    risdiplam and onasemnogene abeparvovec raise SMN protein and are approved for
    SMN1-related 5q SMA. VAPB disease is non-5q and has normal SMN; those agents
    have no mechanistic route to it and must not be curated here as treatments.
    The 21.9-year median survival and the 7-year and 10-year milestones to
    wheelchair and ventilation are, at present, the substance of what can be
    offered: anticipatory management on a predictable timeline.
  proposed_experiments:
  - experiment_id: exp_vapb_wildtype_restoration_preclinical
    name: Test wild-type VAPB restoration in a physiological model
    description: >-
      If haploinsufficiency drives the disease, raising wild-type VAPB should
      rescue it. Test AAV-delivered or allele-selective upregulation of wild-type
      VAPB in the P56S knock-in mouse with motor behaviour, neuromuscular
      junction innervation and ER stress markers as endpoints — a design that
      also discriminates between this entry's two mechanistic hypotheses, since
      restoration should fail if the aggregate is the toxic species.
notes: >-
  Concept decision. This is curated as a `kb/disorders/` Disease. MONDO:0008453
  is a leaf term with one causal gene (VAPB), one OMIM entry (182980) and, in
  practice, one allele; it has no MONDO descendants and is not a union of
  distinct curated entities, so a Grouping would have nothing to unite. Nor is
  it a `has_subtypes` entry on an existing disease: the knowledge base has no
  VAPB/ALS8 parent entry, and it is not a subtype of `Spinal_Muscular_Atrophy`,
  which is anchored on SMN1/SMN2 and models the recessive 5q series. The
  pathograph here is reasonably conserved across reported kindreds, which is the
  test a disorder entry has to pass.

  Scope. This entry covers the pure lower motor neuron, proximal-onset end of
  VAPB p.Pro56Ser disease. It does not attempt to be an ALS8 entry. The honest
  position — and the one the evidence forces — is that the two labels do not
  partition the allele: 42% of molecularly confirmed patients present as pure
  progressive muscular atrophy, 30% of those later acquire upper motor neuron
  signs, and upper motor neuron status does not affect survival. The
  `Abnormal Pyramidal Signs` phenotype and the
  `vapb_p56s_one_allele_many_phenotypes` discussion are curated to record that
  boundary rather than to smuggle ALS into an SMA entry.

  Disagreement with Orphanet, deliberately left standing. Orphanet's definition
  of ORPHA:209335 — the exact-match cross-reference of MONDO:0008453 — defines
  the entity as proximal weakness "without bulbar or pyramidal involvement". The
  2026 series of 78 molecularly confirmed p.Pro56Ser carriers reports upper motor
  neuron signs in 53 of them and bulbar involvement in 21.8%. Both cannot be
  descriptions of the same set of patients. Rather than pick a winner, the
  `Abnormal Pyramidal Signs` and `Bulbar Involvement` phenotypes each carry the
  Orphanet definition as `supports: REFUTE`, so a reader sees a reference
  nosology and a genotype-defined cohort disagreeing about where the entity ends.
  Curating only the cohort would have made the entry look more settled than the
  field is.

  Founder effect. Do not read the eight-family, ~200-affected enumeration as
  eight independent confirmations of pathogenicity. Haplotype analysis places all
  of them, of both Portuguese-Brazilian and African-Brazilian ancestry, on one
  founding chromosome about 23 generations old. The p.Pro56Ser literature is
  therefore geographically and genealogically concentrated, and the Chinese
  kindred reported in 2020 is valuable precisely because it is not part of it.

  One phenotype deliberately left unwired. `Abnormal Pyramidal Signs` is the
  only phenotype with no causal in-edge, and that is the point: wiring it would
  require an upper motor neuron node, and this entry is scoped to the pure lower
  motor neuron end of the p.Pro56Ser spectrum. The only direct evidence for
  corticospinal degeneration is a transgenic mouse in which the corticospinal
  population is lost while spinal motor neurons survive — the opposite of the
  human Finkel phenotype — so a node built on it would import the ALS8 mechanism
  this entry declines to claim. The phenotype is curated because the signs are
  observed in most carriers; it is left unexplained because this entry does not
  have an honest mechanism for them.

  GeneReviews. There is no VAPB- or ALS8-specific GeneReviews chapter. A PubMed
  search restricted to the GeneReviews book (`genereviews[book] AND (VAPB OR
  ALS8 OR "amyotrophic lateral sclerosis type 8")`) returns exactly one record,
  PMID:20301623, the ALS Overview. That is listed in `references` and tagged
  `GeneReviews` so the search is recorded, but nothing is cited from it: its
  indexed content is the chapter's own statement of purpose ("The purpose of
  this overview is to: 1.. Describe the clinical characteristics…"), with no
  clinical, diagnostic or management text to mine, and it is written about ALS
  as a whole rather than about this entity.

  Treatments are supportive only. The `treatments` block carries noninvasive
  ventilation, rehabilitation and genetic counselling, and nothing else, because
  nothing else exists: no disease-modifying therapy has been tested in VAPB
  disease, and the SMN-directed drugs approved for 5q SMA (nusinersen,
  risdiplam, onasemnogene abeparvovec) have no mechanistic route to a non-5q
  disorder with normal SMN — see the `vapb_no_disease_modifying_therapy`
  discussion. Two of the three are evidenced partly from the ALS literature
  rather than from p.Pro56Ser carriers, and each such item is marked
  `supports: PARTIAL` with the extrapolation named in its `explanation` rather
  than smoothed over. Their `target_mechanisms` links deliberately terminate on
  downstream manifestations (`Respiratory Insufficiency`, `Loss of Ambulation`)
  and touch no node on the VAPB chain.

  What is deliberately not curated. No `mechanistic_category`
  classification: `proteotoxic disease` would be the obvious tag, but this
  entry's own HUMAN_MODEL_MISMATCH discussion records that the aggregates may be
  protective and that haploinsufficiency may be the real driver, so asserting
  proteotoxicity as a classification would contradict the mechanism section. No `functional_impact_category`
  on the trigger node's genetic context, because choosing between
  DOMINANT_NEGATIVE and LOSS_OF_FUNCTION would silently resolve the open
  question recorded in `mechanistic_hypotheses`.
📚

References & Deep Research

References

24
PMID:15372378
A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis.
No top-level findings curated for this source.
PMID:16187141
A common founder for amyotrophic lateral sclerosis type 8 (ALS8) in the Brazilian population.
No top-level findings curated for this source.
PMID:16967488
Expanding the phenotypes of the Pro56Ser VAPB mutation: proximal SMA with dysautonomia.
No top-level findings curated for this source.
PMID:42166520
Clinical characterization and natural history of ALS8/VAPB p.Pro56Ser: upper motor neurone signs, survival, and functional milestones in 78 patients.
No top-level findings curated for this source.
PMID:32383641
Peripheral nerve pathology in VAPB-associated amyotrophic lateral sclerosis with dysautonomia in a Chinese family.
No top-level findings curated for this source.
PMID:34440634
The Link between VAPB Loss of Function and Amyotrophic Lateral Sclerosis.
No top-level findings curated for this source.
PMID:17804640
Motor neuron disease-associated mutant vesicle-associated membrane protein-associated protein (VAP) B recruits wild-type VAPs into endoplasmic reticulum-derived tubular aggregates.
No top-level findings curated for this source.
PMID:24252306
Amyotrophic lateral sclerosis (ALS)-associated VAPB-P56S inclusions represent an ER quality control compartment.
No top-level findings curated for this source.
PMID:18555774
The amyotrophic lateral sclerosis 8 protein VAPB is cleaved, secreted, and acts as a ligand for Eph receptors.
No top-level findings curated for this source.
PMID:22131369
VAPB interacts with the mitochondrial protein PTPIP51 to regulate calcium homeostasis.
No top-level findings curated for this source.
PMID:24893131
ER-mitochondria associations are regulated by the VAPB-PTPIP51 interaction and are disrupted by ALS/FTD-associated TDP-43.
No top-level findings curated for this source.
PMID:33972508
Pathomechanisms of ALS8: altered autophagy and defective RNA binding protein (RBP) homeostasis due to the VAPB P56S mutation.
No top-level findings curated for this source.
PMID:26362257
Vapb/Amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying ER stress and autophagic response.
No top-level findings curated for this source.
PMID:23771029
Amyotrophic lateral sclerosis-related VAPB P56S mutation differentially affects the function and survival of corticospinal and spinal motor neurons.
No top-level findings curated for this source.
PMID:23446633
Investigating the contribution of VAPB/ALS8 loss of function in amyotrophic lateral sclerosis.
No top-level findings curated for this source.
PMID:21685205
Downregulation of VAPB expression in motor neurons derived from induced pluripotent stem cells of ALS8 patients.
No top-level findings curated for this source.
PMID:24271015
The amyotrophic lateral sclerosis 8 protein, VAP, is required for ER protein quality control.
No top-level findings curated for this source.
PMID:39870504
A role for mitochondria-ER crosstalk in amyotrophic lateral sclerosis 8 pathogenesis.
No top-level findings curated for this source.
PMID:33461946
Deregulation of phosphatidylinositol-4-phosphate in the development of amyotrophic lateral sclerosis 8.
No top-level findings curated for this source.
PMID:18701194
Vesicle associated membrane protein B (VAPB) is decreased in ALS spinal cord.
No top-level findings curated for this source.
PMID:37470033
Phenotype Presentation and Molecular Diagnostic Yield in Non-5q Spinal Muscular Atrophy.
No top-level findings curated for this source.
PMID:34133501
The history behind ALS type 8: from the first phenotype description to the discovery of VAPB mutation.
No top-level findings curated for this source.
PMID:20301623
Amyotrophic Lateral Sclerosis Overview.
No top-level findings curated for this source.
ORPHA:209335
Autosomal dominant adult-onset proximal spinal muscular atrophy
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Disease Characteristics Research Template
Edison Scientific Literature 29 citations 2026-08-27T11:42:59.340480

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

  • Disease Name: Adult-Onset Proximal Spinal Muscular Atrophy, Autosomal Dominant
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on Adult-Onset Proximal Spinal Muscular Atrophy, Autosomal Dominant covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

  • What is the disease? Provide a concise overview.
  • What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
  • What are the common synonyms and alternative names?
  • Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

  • Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
  • Risk Factors:

    Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases

  • Genetic risk factors (causal variants, susceptibility loci, modifier genes)
  • Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
  • Protective Factors:

    Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases

  • Genetic protective factors (protective variants, modifier alleles)
  • Environmental protective factors (diet, lifestyle, exposures that reduce risk)
  • Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

    Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

  • Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

    Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene

  • Pathogenic Variants:
  • Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
  • Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
  • Variant type/class (missense, frameshift, nonsense, splice-site, structural)
  • Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
  • Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
  • Functional consequences (loss of function, gain of function, dominant negative)
  • Modifier Genes: Genes that modify disease severity or expression
  • Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

    Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

  • Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

    Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases

  • Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

    Search first: CDC databases, WHO, PubMed, NHANES

  • Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

    Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

  • Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

    Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc

  • Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

    Search first: Gene Ontology (GO), Reactome, KEGG, PubMed

  • Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

    Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold

  • Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

    Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA

  • Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

    Search first: ImmPort, Immunome Database, IEDB, Gene Ontology

  • Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

    Search first: PubMed, Gene Ontology, Reactome

  • Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

    Search first: BRENDA, UniProt, KEGG, OMIM, PubMed

  • Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Molecular Profiling (if available):
  • Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
  • Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
  • Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
  • Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
  • Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
  • Advanced Technologies (if applicable):
  • Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
  • Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
  • Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
  • Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

  • Organ Level:
  • Primary organs directly affected
  • Secondary organ involvement (complications, secondary effects)
  • Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

    Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT

  • Tissue and Cell Level:
  • Specific tissue types affected (epithelial, connective, muscle, nervous)
  • Specific cell populations targeted (with Cell Ontology terms)

    Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB

  • Subcellular Level:
  • Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

    Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas

  • Localization:
  • Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
  • Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

  • Onset:
  • Typical age of onset (congenital, pediatric, adult, geriatric)
  • Onset pattern (acute, subacute, chronic, insidious)

    Search first: OMIM, Orphanet, HPO, PubMed

  • Progression:
  • Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
  • Progression rate (rapid, slow, variable)
  • Disease course pattern (episodic, relapsing-remitting, progressive, stable)
  • Disease duration (self-limited, chronic lifelong)

    Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM

  • Patterns:
  • Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
  • Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

  • Epidemiology:
  • Prevalence (cases per 100,000 at given time)
  • Incidence (new cases per 100,000 per year)

    Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries

  • For Genetic Etiology:
  • Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
  • Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
  • Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
  • Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
  • Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
  • Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
  • Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
  • Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
  • Population Demographics:
  • Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
  • Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
  • Geographic distribution of specific variants
  • Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
  • Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

  • Clinical Tests:
  • Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
  • Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
  • Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
  • Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
  • Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
  • Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
  • Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
  • Genetic Testing:

    Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen

  • Overview of recommended genetic testing approach
  • Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
  • Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
  • Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
  • Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
  • Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
  • Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
  • FISH > Search first: ClinVar, cytogenetics databases, PubMed
  • Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
  • Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
  • Omics-Based Diagnostics (if applicable):
  • RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
  • Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
  • Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
  • Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
  • Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
  • Clinical Criteria:
  • Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
  • Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
  • Screening:
  • Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

  • Survival and Mortality:
  • Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
  • Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
  • Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
  • Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
  • Morbidity and Function:
  • Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
  • Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
  • Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
  • Disease Course:
  • Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
  • Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
  • Prediction:
  • Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
  • Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

  • Pharmacotherapy:
  • Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
  • Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
  • Advanced Therapeutics:
  • Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
  • Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
  • RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
  • Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
  • Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
  • Surgical and Interventional:
  • Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
  • Supportive and Rehabilitative:
  • Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
  • Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
  • Experimental:
  • Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
  • Treatment Outcomes:
  • Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
  • Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
  • Treatment Strategy:
  • Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
  • Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
  • Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest NCIT (NCI Thesaurus) clinical-intervention terms where applicable.

13. Prevention

  • Prevention Levels:
  • Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
  • Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
  • Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
  • Immunization: Vaccine strategies (if applicable)

    Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database

  • Screening and Early Detection:
  • Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
  • Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
  • Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
  • Behavioral Interventions: Lifestyle modifications to reduce risk

    Search first: CDC, WHO, behavioral intervention databases, Cochrane Library

  • Counseling: Genetic counseling (risk assessment, family planning guidance)

    Search first: NSGC resources, ACMG guidelines, GeneReviews

  • Public Health:
  • Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
  • Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
  • Prophylaxis: Preventive medications or procedures

    Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

  • Taxonomy: Species affected (with NCBI Taxon identifiers)

    Search first: NCBI Taxonomy

  • Breed: Specific breeds affected (with VBO identifiers if applicable)

    Search first: VBO (Vertebrate Breed Ontology)

  • Gene: Orthologous genes in other species (with NCBI Gene IDs)

    Search first: NCBI Gene

  • Natural Disease:
  • Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
  • Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
  • Comparative Biology:
  • Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
  • Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
  • Transmission (if applicable):
  • Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
  • Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

  • Model Types:
  • Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
  • Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
  • Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
  • Genetic Models:
  • Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
  • Model Characteristics:
  • Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
  • Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
  • Applications:
  • Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
  • Resources:
  • Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic and clinical claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes from abstracts where possible to support key statements
  • Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (NCIT terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Adult-Onset Proximal Spinal Muscular Atrophy, Autosomal Dominant

Executive summary and scope

Adult-onset proximal spinal muscular atrophy, autosomal dominant is an ultra-rare inherited lower-motor-neuron disease mapped to MONDO:0008453. In the literature it is usually treated as the Finkel-type spinal muscular atrophy/amyotrophic lateral sclerosis type 8 (ALS8) spectrum caused by heterozygous pathogenic variation in VAPB, particularly p.Pro56Ser (P56S). The classic phenotype is adult-onset, slowly progressive proximal weakness and neurogenic muscle atrophy, but the same variant can produce slowly progressive ALS or, less commonly, rapidly progressive conventional ALS. Thus, Finkel SMA is best considered one end of a variable VAPB-associated motor-neuron-disease spectrum rather than a uniformly discrete syndrome. Open Targets identifies VAPB as the only target associated with the exact MONDO disease label and links the association to the original discovery paper, PMID 15372378. Open Targets, accessed through the disease-target record (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant)

The evidence base remains small. Most human data derive from extended Brazilian kindreds rather than population cohorts, EHR studies, or randomized trials. Recent disease-specific research in 2023–2024 was sparse; a 2023 Colombian report expanded the geographic phenotype, while a 2024 review emphasized that molecularly distinct non-5q SMAs require next-generation sequencing and still lack the approved therapies available for SMN1-related SMA. Accordingly, many epidemiologic frequencies, penetrance estimates, quality-of-life scores, and treatment-response statistics remain unknown.

The following table summarizes the principal knowledge-base fields.

domain evidence-supported value ontology/database annotation suggestions evidence type/limitations
Disease entity Adult-onset proximal spinal muscular atrophy, autosomal dominant; clinically overlaps the Finkel-type SMA / ALS8 motor-neuron-disease spectrum; MONDO:0008453 (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant, larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, borgese2021thelinkbetween pages 1-2) MONDO:0008453; disease synonyms to capture: Finkel type SMA, late-onset SMA, ALS8-spectrum motor neuron disease MONDO/Open Targets plus literature synthesis; legacy disease naming is heterogeneous and may overlap with ALS8 rather than a fully separate entity
Key identifiers MONDO resolved as MONDO:0008453; Open Targets links the disease specifically to VAPB; OMIM/Orphanet/ICD/MeSH mappings not securely resolved from retrieved evidence and should be marked unresolved pending manual curation (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant) MONDO:0008453; Open Targets disease-target association; OMIM/Orphanet/ICD/MeSH: unresolved Identifier evidence strong for MONDO/VAPB only; do not invent external IDs
Causal gene VAPB (VAMP associated protein B and C) is the sole disease-associated target recovered in Open Targets for this disease label (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant) HGNC gene: VAPB; Ensembl target in Open Targets: ENSG00000124164 Disease-target evidence is consistent, but not a substitute for full locus curation
Pathogenic variant Recurrent causative variant is VAPB p.Pro56Ser (P56S), a missense change in the MSP domain; described as codon 56 proline-to-serine change in exon 2 on chr20q13.33 (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, murage2023characterisationofa pages 30-33, borgese2021thelinkbetween pages 7-9) HGVS protein: p.Pro56Ser; variant class: missense SNV; germline Retrieved evidence supports pathogenicity, but population allele frequency and ClinVar assertion details were not retrieved here
Inheritance Autosomal dominant (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, murage2023characterisationofa pages 30-33, borgese2021thelinkbetween pages 1-2) HPO inheritance term suggestion: Autosomal dominant inheritance [HP:0000006] Strong human family evidence; penetrance not quantitatively established in retrieved sources
Founder / population Initially described in large Brazilian families; evidence supports a Portuguese founder effect in many reported ALS8/Finkel-spectrum families, although review literature notes broader occurrence beyond Brazil (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, borgese2021thelinkbetween pages 21-22, borgese2021thelinkbetween pages 1-2) Population annotation suggestion: founder effect in Brazilian/Portuguese ancestry; geographic note rather than ontology ID Founder interpretation is literature-based and may not apply to every reported family
Typical onset Late adult/adult onset, average around 50 years (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, larroquette2015vapbamyotrophiclateralsclerosis pages 14-15) HPO onset suggestion: Adult onset [HP:0003581] Mean age estimate is derived from family-series literature; precise distribution not established in retrieved evidence
Core phenotype Slowly progressive lower motor neuron syndrome with proximal weakness and muscle atrophy; clinical heterogeneity ranges from late-onset SMA/Finkel phenotype to slowly progressive ALS and, less commonly, typical severe rapidly progressive ALS (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, murage2023characterisationofa pages 30-33, borgese2021thelinkbetween pages 1-2) HPO suggestions: Proximal muscle weakness [HP:0003701], Muscle atrophy [HP:0003202], Fasciculations [HP:0002380], Lower motor neuron dysfunction/degeneration [suggest disease annotation], Motor neuron atrophy [HP:0007373] Phenotype is well supported but frequency of each manifestation was not quantified in retrieved sources
Electrophysiology / pathology Needle EMG shows fasciculations in limbs and tongue, large motor unit potentials with reduced recruitment; sensory studies and motor nerve conduction may remain normal. Muscle pathology is neurogenic, with chronic denervation/reinnervation-type changes (murage2023characterisationofa pages 30-33, larroquette2015vapbamyotrophiclateralsclerosis pages 7-9) Diagnostic annotation suggestions: EMG evidence of chronic neurogenic change; muscle biopsy showing neurogenic atrophy Detailed clinical-diagnostic data came from limited family/series evidence and model-human comparison
Primary anatomy affected Lower motor neurons, especially spinal cord ventral horn and brainstem motor neurons; downstream involvement of neuromuscular junction and skeletal muscle (larroquette2015vapbamyotrophiclateralsclerosis pages 10-12, larroquette2015vapbamyotrophiclateralsclerosis pages 9-10) UBERON suggestions: spinal cord ventral horn, brainstem motor nucleus, skeletal muscle, neuromuscular junction; CL suggestions: motor neuron Strong model support and consistent human clinical inference; human tissue data in retrieved set are limited
Subcellular localization / mechanism VAPB is an ER membrane protein; p.Pro56Ser causes mutant protein misfolding/aggregation tendency, loss of normal ER localization/function, altered ER homeostasis, disrupted ER-mitochondria tethering/contact sites, abnormal Ca2+ handling, and NMJ denervation/reinnervation changes (borgese2021thelinkbetween pages 7-9, larroquette2015vapbamyotrophiclateralsclerosis pages 14-15, larroquette2015vapbamyotrophiclateralsclerosis pages 15-17, murage2023characterisationofa pages 30-33) GO/CC suggestions: endoplasmic reticulum membrane, mitochondria-associated ER membrane/contact site, neuromuscular junction; GO/BP suggestions: ER stress response, unfolded protein response, calcium homeostasis, autophagy, intracellular protein transport Mechanistic evidence is largely from cell and animal models; exact dominant-negative vs haploinsufficiency balance remains debated
Mechanistic interpretation Current understanding favors major loss-of-function/haploinsufficiency of VAPB, with possible dominant-negative effects from sequestration of wild-type VAP proteins in some systems (borgese2021thelinkbetween pages 7-9, larroquette2015vapbamyotrophiclateralsclerosis pages 15-17, borgese2021thelinkbetween pages 1-2) Mechanism tags: loss of function; possible dominant negative Important unresolved issue: overexpression systems emphasize aggregation, whereas patient-derived cells may show little visible aggregation
Environmental / protective factors No disease-specific environmental triggers, lifestyle risks, infectious causes, or protective factors were identified in retrieved evidence (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, borgese2021thelinkbetween pages 1-2) Mark as no disease-specific evidence found Evidence gap, not evidence of absence
Diagnostics Best-supported approach: clinical recognition of adult-onset proximal/lower-motor-neuron syndrome plus electrophysiology and confirmatory molecular testing of VAPB, especially p.Pro56Ser; broad non-5q SMA / motor neuron disease gene panels or exome/genome sequencing are reasonable when phenotype is atypical (murage2023characterisationofa pages 30-33, larroquette2015vapbamyotrophiclateralsclerosis pages 3-4) Suggested testing workflow: EMG/NCS, targeted VAPB testing, multigene motor neuron disease/non-5q SMA panel, WES/WGS if negative No disease-specific formal guideline retrieved; recommendation is evidence-bounded inference from reported cases and non-5q SMA review context
Differential diagnosis Differentiate from 5q-SMA (SMN1-related), other non-5q SMAs, hereditary motor neuropathies, and familial/sporadic ALS presentations (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, borgese2021thelinkbetween pages 1-2) Differential-diagnosis tags: 5q-SMA, non-5q SMA, hereditary motor neuropathy, ALS No standardized disease-specific differential algorithm retrieved
Epidemiology Ultra-rare; no robust prevalence or incidence estimate was identified in retrieved sources. Evidence is based mainly on kindreds and founder-associated case series (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, murage2023characterisationofa pages 30-33) Orphan disease flag; prevalence/incidence unresolved Major evidence gap
Prognosis Course is usually slowly progressive in classic Finkel/ALS8 families, but marked intrafamilial/interfamilial variability exists, including rapidly progressive ALS phenotypes (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, borgese2021thelinkbetween pages 1-2) Prognosis tags: chronic progressive disease; variable expressivity No robust survival curves or validated prognostic biomarkers retrieved
Treatment No approved disease-specific therapy for VAPB-associated adult-onset proximal SMA/Finkel disease was identified; management is supportive and extrapolated from motor neuron disease care (rehabilitation, mobility, respiratory/nutritional surveillance as clinically indicated) (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, borgese2021thelinkbetween pages 1-2) NCIT suggestions: Physical Therapy, Occupational Therapy, Supportive Care, Genetic Counseling Evidence gap for disease-specific efficacy studies; no relevant registered interventional trial was retrieved
Prevention / counseling Primary prevention is not established. Secondary/tertiary prevention centers on early genetic diagnosis, cascade testing in at-risk relatives, and reproductive/genetic counseling for autosomal-dominant transmission risk (borgese2021thelinkbetween pages 1-2) NCIT suggestion: Genetic Counseling; HPO inheritance annotation Counseling recommendation inferred from monogenic AD disease practice; no disease-specific counseling guideline retrieved
Model systems Disease-relevant models include VAPB P56S knock-in mice, VAPB transgenic/knockout mice, Drosophila VAP P58S models, rat ALS8 models, NSC34 motor-neuron-like cells, and patient-derived iPSC motor neurons (larroquette2015vapbamyotrophiclateralsclerosis pages 10-12, larroquette2015vapbamyotrophiclateralsclerosis pages 14-15, borgese2021thelinkbetween pages 7-9, larroquette2015vapbamyotrophiclateralsclerosis pages 7-9) Model resources: mouse KI/KO/transgenic, fly model, rat model, iPSC motor neuron, cell line model Strong preclinical ecosystem, but not all models recapitulate the slow human lower-motor-neuron phenotype equally well

Table: This table condenses the highest-confidence, evidence-supported facts for VAPB-associated adult-onset proximal spinal muscular atrophy/Finkel-type disease in a knowledge-base-friendly format. It highlights established findings, annotation suggestions, and the main evidence gaps requiring manual curation.

1. Disease information

Definition. This is a hereditary, adult-onset degeneration/dysfunction of lower motor neurons, producing chronic denervation, proximal weakness, fasciculations, and muscle atrophy. “Proximal SMA” here must not be conflated with common 5q SMA, which is caused by biallelic SMN1 defects. VAPB disease is non-5q and autosomal dominant. Human presentations range from pure lower-motor-neuron/Finkel-type SMA to upper-and-lower-motor-neuron ALS8 (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4).

Identifiers and synonyms. Securely resolved: MONDO:0008453 and causal target VAPB/ENSG00000124164. Useful synonyms are adult-onset proximal spinal muscular atrophy, autosomal dominant; autosomal dominant late-adult spinal muscular atrophy; Finkel-type SMA; late-onset SMA, Finkel type; and, when upper-motor-neuron involvement occurs, ALS8 or VAPB-associated motor neuron disease. Exact OMIM, Orphanet, MeSH, ICD-10, and ICD-11 mappings were not securely recoverable and should be manually curated rather than inferred. ICD coding will generally fall under motor-neuron disease or spinal muscular atrophy, but no unique disease-specific ICD code was demonstrated in the retrieved evidence (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant).

Evidence provenance. The foundational 1981 report described two extended families with approximately 80 affected members. Subsequent molecular work studied a large Brazilian family and six additional kindreds. Another summarized pedigree contained 28 affected people across four generations. These are aggregated pedigree/publication data, not individual-level EHR data (murage2023characterisationofa pages 30-33).

2. Etiology, risk, and protective factors

The primary cause is a germline heterozygous pathogenic VAPB variant, most characteristically p.Pro56Ser. Autosomal-dominant inheritance makes an affected heterozygote’s transmission probability approximately 50% per pregnancy, although clinical risk also depends on age-dependent penetrance and variable expression. Quantitative penetrance has not been established in the retrieved studies (murage2023characterisationofa pages 30-33, borgese2021thelinkbetween pages 7-9).

The principal established risk factors are carrying the familial variant, increasing age, and family history. No reproducible sex difference was observed in the family evidence. No environmental toxin, infection, occupational exposure, diet, smoking behavior, or lifestyle factor has been shown to cause or materially modify VAPB-Finkel disease. Likewise, no validated protective allele, modifier gene, diet, medication, or gene–environment interaction is known. These are evidence gaps, not proof that modifiers do not exist (murage2023characterisationofa pages 30-33, larroquette2015vapbamyotrophiclateralsclerosis pages 3-4).

A Portuguese founder has been proposed for many p.Pro56Ser kindreds, with dissemination into Brazil and reports in North America, Germany, China, and elsewhere. However, broader geographic occurrence means that founder status should not be assumed for every p.Pro56Ser carrier (borgese2021thelinkbetween pages 21-22, borgese2021thelinkbetween pages 1-2).

3. Phenotypes

The phenotype is variably expressed and frequencies are not robustly quantified.

  • Proximal limb weakness—usually insidious, adult-onset, mild-to-moderate initially, and progressive. Lower limbs are commonly prominent. Suggested HPO: Proximal muscle weakness, HP:0003701; Lower-limb muscle weakness, HP:0007340.
  • Muscle atrophy—a clinical sign secondary to chronic denervation. Suggested HPO: Muscle atrophy, HP:0003202.
  • Fasciculations, including limb and tongue fasciculations. Suggested HPO: Fasciculations, HP:0002380.
  • Muscle cramps and sometimes postural tremor are reported within the broader ALS8 phenotype. Suggested HPO: Muscle cramps, HP:0003394; Postural tremor, HP:0002173.
  • Lower-motor-neuron dysfunction—large motor-unit potentials, reduced recruitment, denervation/reinnervation, weakness, and reduced muscle bulk. Sensory examination and sensory conduction are generally preserved, supporting a motor-neuron rather than generalized peripheral-neuropathy process (murage2023characterisationofa pages 30-33).
  • Upper-motor-neuron signs are absent in the classic Finkel SMA phenotype but can occur in ALS8-spectrum relatives. This distinction explains why the same familial variant has been described as SMA, atypical ALS, or conventional ALS (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, larroquette2015vapbamyotrophiclateralsclerosis pages 9-10).
  • Bulbar/respiratory involvement is not a defining early feature of classic slowly progressive Finkel SMA, although tongue fasciculations and ALS-spectrum progression make surveillance appropriate. Disease-specific frequencies are unavailable.
  • Cognition/behavior are generally not central to the classic definition; available evidence is insufficient to assign reliable frequencies or HPO annotations.

The best-supported onset estimate is an average near 50 years, followed by chronic slow progression in the classic phenotype. Severe rapidly progressive ALS is a documented but less typical expression (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, larroquette2015vapbamyotrophiclateralsclerosis pages 14-15). No disease-specific EQ-5D, SF-36, PROMIS, or utility estimates were found. Expected quality-of-life effects arise from impaired walking, transfers, upper-limb tasks, fatigue, cramps, and eventual dependence on mobility or respiratory support, but these have not been quantified specifically for Finkel disease.

4. Genetic and molecular information

Gene. VAPB encodes VAMP-associated protein B/C, an integral endoplasmic-reticulum adaptor and membrane-contact-site protein. Open Targets lists it as the sole target for MONDO:0008453 (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant).

Variant. The recurrent lesion is VAPB p.Pro56Ser, a germline missense variant in exon 2 at chromosome 20q13.33. It changes a highly conserved proline in the N-terminal major-sperm-protein domain, close to the FFAT-motif-binding surface. The original molecular-discovery paper is Nishimura et al., American Journal of Human Genetics, published November 2004, DOI 10.1086/425287, PMID 15372378. Its abstract states that the same mutation occurred in kindreds with “different clinical courses, such as ALS8, late-onset SMA, and typical severe ALS with rapid progression,” directly supporting variable expressivity (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant).

The variant is pathogenic based on segregation in multiple affected families, recurrence, functional disruption, and disease-model phenotypes. The retrieved material did not provide a definitive current ClinVar star status, HGNC ID, dbSNP accession, genomic HGVS expression, or gnomAD/TOPMed allele frequency; these should be retrieved directly against the reference transcript before production annotation. It is a constitutional germline variant, not a somatic cancer alteration.

Functional consequence. p.Pro56Ser makes VAPB unstable, aggregation-prone, and functionally deficient. Overexpression systems show recruitment of wild-type VAP proteins into mutant ER-derived aggregates, supporting a dominant-negative component. Physiologic knock-in and patient-cell evidence increasingly favors loss of function/haploinsufficiency, because visible aggregates are not consistently found in patient-derived fibroblasts or iPSC motor neurons (borgese2021thelinkbetween pages 7-9). These mechanisms need not be mutually exclusive.

No validated human modifier gene, protective allele, disease-specific methylation signature, chromosomal rearrangement, repeat expansion, or recurrent structural variant is established. Drosophila genetic screens identified modifiers in proteolysis, vesicle/endocytic trafficking, apoptosis, and lipid-droplet biology, but these are experimental candidates rather than clinically validated human modifiers.

5. Environmental information

This is a monogenic neurodegenerative disease. There is no established causal role for toxins, radiation, pollution, occupation, smoking, alcohol, diet, exercise pattern, or infectious agents. Exercise and rehabilitation can preserve function but should not be represented as preventing the genetic disease. There is no zoonotic or transmissible component. Environmental and lifestyle datasets specific to VAPB-Finkel SMA were not found.

6. Mechanism and pathophysiology

A defensible causal chain is:

  1. Upstream genetic trigger: heterozygous VAPB p.Pro56Ser alters the conserved MSP domain.
  2. Protein-level defect: mutant VAPB is unstable, poorly soluble, mislocalized, and deficient in normal ER-adaptor interactions; in some systems it sequesters wild-type VAPB and interacting proteins.
  3. Organelle dysfunction: reduced functional VAPB perturbs ER-to-Golgi trafficking, phosphoinositide/lipid homeostasis, ER proteostasis, autophagy, and ER–mitochondria membrane contacts.
  4. Stress signaling: impaired ER homeostasis activates parts of the unfolded-protein/integrated-stress response. In knock-in motor neurons, PDI, BiP/GRP78, and phosphorylated eIF2α increase before overt motor deficits, while ATF4, ATF6, and CHOP are not uniformly increased—evidence for partial or compensated stress rather than a single terminal-apoptosis program (larroquette2015vapbamyotrophiclateralsclerosis pages 14-15, larroquette2015vapbamyotrophiclateralsclerosis pages 15-17).
  5. Calcium/energy consequences: impaired VAPB-dependent contact-site tethering disturbs mitochondrial calcium handling and bioenergetic coupling. This is mechanistically plausible and strongly supported experimentally, but direct confirmation in human Finkel tissue remains limited.
  6. Selective cellular injury: long, metabolically demanding spinal and brainstem lower motor neurons become dysfunctional, followed by distal axonal and neuromuscular-junction denervation.
  7. Tissue/clinical outcome: compensatory sprouting and reinnervation initially preserve motor units, but chronic denervation produces grouped muscle-fiber atrophy, proximal weakness, fasciculations, cramps, and progressive disability (larroquette2015vapbamyotrophiclateralsclerosis pages 9-10, larroquette2015vapbamyotrophiclateralsclerosis pages 7-9).

Suggested GO biological-process annotations: response to endoplasmic-reticulum stress; unfolded-protein response; autophagy; calcium-ion homeostasis; intracellular protein transport; ER-to-Golgi vesicle-mediated transport; regulation of lipid transport; axonal transport; neuromuscular-junction development; motor-neuron apoptotic process. Suggested GO cellular components: endoplasmic-reticulum membrane; ER–mitochondrion membrane contact site; Golgi apparatus; cytoplasmic protein-containing aggregate; axon; presynaptic active zone; neuromuscular junction. Suggested CL terms: motor neuron (CL:0000100), spinal motor neuron, skeletal muscle fiber, and Schwann cell—the latter two primarily as downstream/secondary participants.

No validated disease-specific human transcriptomic, proteomic, metabolomic, lipidomic, spatial-transcriptomic, or single-cell signature is ready for clinical use. Patient-derived iPSC motor neurons and CRISPR-corrected isogenic cells are important emerging systems, but findings remain research-stage (landry2026investigationsofals pages 146-153).

7. Anatomical structures affected

The primary body system is the somatic motor nervous system. Principal sites are spinal-cord anterior/ventral-horn motor neurons, brainstem motor nuclei, their peripheral motor axons, and neuromuscular junctions. Skeletal muscle is affected secondarily through denervation. Sensory neurons and sensory nerves are relatively spared in the classic syndrome (murage2023characterisationofa pages 30-33, larroquette2015vapbamyotrophiclateralsclerosis pages 10-12).

Suggested UBERON annotations are spinal cord, ventral horn of spinal cord, brainstem, motor nucleus, peripheral nerve, and skeletal muscle organ. At the subcellular level, the ER membrane and ER–mitochondria contact sites are central. Mouse data show VAPB enrichment in lower and brainstem motor neurons, with lower expression in cerebrum, cerebellum, hippocampus, and glia (larroquette2015vapbamyotrophiclateralsclerosis pages 10-12). Weakness can be bilateral but may be clinically asymmetric; no fixed lateralization is defining.

8. Temporal development

Onset is chronic and insidious in adulthood, averaging approximately 50 years in reported ALS8/Finkel families. The classic course is slowly progressive over many years, without spontaneous remission. Some carriers instead develop rapidly progressive ALS, demonstrating substantial intra- and interfamilial variability (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4).

A practical staging framework—not a validated formal scale—is: early focal/proximal weakness and cramps; intermediate multiregional weakness with mobility impairment; advanced loss of ambulation or upper-limb function; and, in ALS-like cases, bulbar or respiratory insufficiency. There are no established critical treatment windows, but mechanistic models show ER stress and autophagic responses before motor deficits, supporting the general principle that future molecular treatment may work best presymptomatically or early (larroquette2015vapbamyotrophiclateralsclerosis pages 14-15, larroquette2015vapbamyotrophiclateralsclerosis pages 15-17).

9. Inheritance and population

Inheritance is autosomal dominant, with variable expressivity and likely age-dependent penetrance. Genetic anticipation, germline mosaicism, and a consanguinity effect have not been demonstrated. Consanguinity is not expected to be a major determinant of an AD disorder. Carrier frequency cannot be estimated reliably because population prevalence and variant frequency are unknown (murage2023characterisationofa pages 30-33, borgese2021thelinkbetween pages 7-9).

The disease is ultra-rare. No defensible prevalence per 100,000 or annual incidence was found. Published evidence is enriched for Brazilian families of Portuguese ancestry, so case counts cannot be used as population rates. One large pedigree summary reports 28 affected members over four generations; the original clinical description reported two families with about 80 affected members. No consistent male:female difference was observed (murage2023characterisationofa pages 30-33).

10. Diagnostics

Diagnosis should combine phenotype, electrodiagnosis, exclusion of mimics, and molecular confirmation.

  1. Clinical assessment: document distribution and progression of weakness, atrophy, fasciculations, reflexes, upper-motor-neuron signs, bulbar function, cognition, family history, and a three-generation pedigree.
  2. EMG/NCS: needle EMG may show limb and tongue fasciculations, chronic large-amplitude motor-unit potentials, and reduced recruitment. Sensory responses and motor conduction velocities can remain normal, supporting anterior-horn-cell disease rather than demyelinating neuropathy (murage2023characterisationofa pages 30-33).
  3. Laboratory testing: CK may be normal or mildly elevated in neurogenic disorders but no disease-specific range was recovered. Routine blood tests mainly exclude acquired mimics.
  4. Muscle biopsy: generally unnecessary after molecular confirmation. When performed, it shows chronic neurogenic atrophy, including groups of small fibers, internal nuclei, and denervation/reinnervation patterns (larroquette2015vapbamyotrophiclateralsclerosis pages 7-9).
  5. Imaging and functional assessment: MRI is principally used to exclude compressive myelopathy or structural disease; pulmonary function, swallowing evaluation, and mobility scales should follow clinical involvement. No diagnostic imaging biomarker exists.
  6. Genetic testing: in a family with a known variant, use targeted VAPB testing. In an unresolved adult lower-motor-neuron syndrome, use a comprehensive non-5q SMA/hereditary motor-neuropathy/ALS panel including VAPB, SMN1, SETX, BICD2, DYNC1H1, TRPV4, VRK1, SIGMAR1, SOD1, FUS, TARDBP, C9orf72, and other phenotype-appropriate genes. Copy-number analysis and SMN1 dosage should be technically covered where relevant. WES or WGS is appropriate after negative panel testing or for atypical families. Repeat-expansion testing, particularly C9orf72, requires a validated dedicated method because standard exome sequencing may miss it.
  7. Tests generally not indicated as first-line: karyotype, FISH, CMA, mitochondrial sequencing, liquid biopsy, proteomics, or epigenomics, unless another phenotype suggests them.

Important differentials include 5q-SMA type IV, Kennedy disease/SBMA, other dominant non-5q SMAs and hereditary motor neuropathies, multifocal motor neuropathy, adult-onset Pompe disease, inclusion-body myositis, cervical/lumbosacral myelopathy, and familial/sporadic ALS. Molecular confirmation is particularly important because VAPB-related SMA and ALS overlap clinically.

No universally accepted disease-specific clinical criteria exist. The molecular diagnosis should use ACMG/AMP variant interpretation and segregation analysis; genetic counseling should accompany testing.

11. Outcome and prognosis

Classic Finkel disease usually progresses slowly, but there are no reliable five- or ten-year survival estimates, disease-specific mortality rates, or life-expectancy tables. Prognosis cannot safely be inferred from conventional ALS because some VAPB families survive far longer, whereas other carriers have severe rapidly progressive ALS (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4, borgese2021thelinkbetween pages 1-2).

Morbidity includes progressive gait impairment, falls, difficulty climbing stairs or rising, upper-limb functional loss, cramps, fatigue, and eventual dependence on assistive devices. Respiratory and bulbar complications are likely to drive mortality in ALS-like disease but are not well quantified in pure Finkel SMA. Age at onset, baseline functional involvement, rate of spread, and respiratory status are clinically relevant, but no validated VAPB-specific prognostic biomarker exists.

12. Treatment and current applications

There is no approved VAPB-specific disease-modifying treatment and no disease-specific interventional trial was identified in the ClinicalTrials.gov search. Nusinersen, risdiplam, and onasemnogene abeparvovec increase or replace SMN protein and are approved for SMN1-related 5q SMA; their mechanism does not address VAPB disease and they should not be represented as treatments for Finkel SMA.

Current real-world management is multidisciplinary and supportive:

  • individualized physiotherapy, stretching, low-to-moderate-intensity conditioning, fall prevention, orthoses, mobility aids, and occupational therapy;
  • management of cramps, spasticity if present, pain, fatigue, sleep, and mood using standard symptomatic practice;
  • serial respiratory assessment and non-invasive ventilation/cough assistance when indicated;
  • swallowing and nutritional assessment if bulbar involvement develops;
  • speech/communication support and assistive technology;
  • orthopedic management of contracture or deformity when needed; surgery is not disease-modifying;
  • genetic counseling and psychosocial support.

Suggested NCIt intervention concepts are Supportive Care, Physical Therapy, Occupational Therapy, Respiratory Therapy, Noninvasive Ventilation, Nutritional Support, Assistive Device, and Genetic Counseling. Exact NCIt codes should be resolved against the current release.

Experimental strategies suggested by models include restoring wild-type VAPB function, suppressing mutant transcript/protein, correcting p.Pro56Ser, improving ER proteostasis, stabilizing ER–mitochondria contacts, and modulating autophagy or stress responses. These remain preclinical. Mouse overexpression of wild-type VAPB has slowed denervation in other ALS models, but that does not establish efficacy in human ALS8/Finkel disease (borgese2021thelinkbetween pages 21-22).

13. Prevention

No vaccine, medication, environmental modification, or lifestyle intervention prevents expression of the pathogenic allele.

  • Primary prevention: reproductive counseling, prenatal diagnosis, or preimplantation genetic testing may reduce transmission when the familial variant is known; these are preference-sensitive options, not obligatory prevention.
  • Secondary prevention: cascade testing of adult relatives after informed consent can identify presymptomatic carriers. Population or newborn screening is not currently justified because prevalence is extremely low and no proven presymptomatic disease-modifying therapy exists.
  • Tertiary prevention: early rehabilitation, fall prevention, contracture management, vaccination against routine respiratory pathogens, respiratory surveillance, nutrition/swallow management, and timely assistive devices may prevent complications.

Predictive testing should address age-dependent penetrance, uncertain severity, psychological effects, privacy, and reproductive choices.

14. Other species and natural disease

No naturally occurring veterinary disease securely homologous to human VAPB p.Pro56Ser Finkel SMA was identified. Consequently, no breed-specific VBO annotation, animal prevalence, veterinary transmission concern, or zoonotic potential can be assigned. VAPB is evolutionarily conserved, enabling engineered mouse, rat, fly, nematode, yeast, and cellular models, but engineered phenocopy is not equivalent to natural animal disease.

15. Model organisms and experimental systems

Mouse. Physiologic Vapb P56S knock-in mice develop late, slowly progressive motor impairment, partial denervation, neurogenic muscle pathology, ER stress, ubiquitinated-protein accumulation, and autophagic responses. Weakness becomes apparent around 11 months, while molecular pathology precedes behavior. At the NMJ, mutant mice had 29.3 ± 1.9 presynaptic boutons versus 16.6 ± 1.0 in wild type, enlarged endplates, fragmentation, and chronic denervation/reinnervation (larroquette2015vapbamyotrophiclateralsclerosis pages 14-15, larroquette2015vapbamyotrophiclateralsclerosis pages 9-10). Larroquette et al., published September 2015, DOI 10.1093/hmg/ddv360, is the key model study. Limitations include mild phenotype, preserved motor-neuron counts, and incomplete reproduction of severe human ALS.

Transgenic and knockout mice. Overexpression models variably form aggregates and often show weak behavioral phenotypes; knockout animals show only mild impairment. These discrepancies are central to the unresolved balance between toxic aggregation, dominant-negative activity, and haploinsufficiency (borgese2021thelinkbetween pages 7-9, larroquette2015vapbamyotrophiclateralsclerosis pages 15-17).

Drosophila. The homologous VAP P58S model produces aggregation, synaptic defects, impaired BMP signaling, and motor decline. Genetic screens identify trafficking, proteolysis, apoptosis, and lipid-droplet pathways as modifiers. Advantages are rapid in-vivo screening; limitations are invertebrate neuroanatomy and overexpression artifacts.

Rat. A 2023 University of Edinburgh study characterized an ALS8 rat model and summarized the three human clinical expressions—late-onset SMA, slowly progressive atypical ALS, and rapidly progressive ALS. This is recent but thesis-level rather than mature clinical evidence. DOI 10.7488/era/2973, January 2023 (murage2023characterisationofa pages 30-33).

Cellular systems. NSC34 motor-neuron-like cells expressing p.Pro56Ser show increased susceptibility to ER-stress-related death. Patient fibroblasts and iPSC-derived motor neurons are more physiologic and do not consistently show the conspicuous aggregates seen in overexpression models. CRISPR-corrected isogenic iPSC lines permit direct attribution of stress and ER–mitochondria phenotypes to p.Pro56Ser (landry2026investigationsofals pages 146-153, borgese2021thelinkbetween pages 7-9).

Evidence assessment and research priorities

The most authoritative human evidence remains the 2004 mutation-discovery study and the original extended-family observations. The strongest mechanistic evidence comes from knock-in mice, cell systems, and patient-derived iPSC models—not human motor-neuron tissue. Recent work has refined VAPB’s roles in ER contact sites and stress signaling, but 2023–2024 produced little disease-specific clinical epidemiology or therapeutic evidence.

Priority gaps are: prospective genotype-defined natural-history cohorts; age-specific penetrance and survival; standardized phenotype frequencies; respiratory, cognitive, and quality-of-life outcomes; direct gnomAD/ClinVar transcript-level curation; patient-derived motor-neuron multi-omics; biomarkers of progression; and genotype-specific interventional trials. Until these exist, database entries should explicitly distinguish established human genetic/clinical facts, model-supported mechanisms, and clinical-management extrapolations.

References

  1. (OpenTargets Search: Adult-onset proximal spinal muscular atrophy, autosomal dominant): Open Targets Query (Adult-onset proximal spinal muscular atrophy, autosomal dominant, 1 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

  2. (larroquette2015vapbamyotrophiclateralsclerosis pages 3-4): Frédérique Larroquette, Lesley Seto, Perrine L. Gaub, Brishna Kamal, Deeann Wallis, Roxanne Larivière, Joanne Vallée, Richard Robitaille, and Hiroshi Tsuda. Vapb/amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying er stress and autophagic response. Human molecular genetics, 24 22:6515-29, Sep 2015. URL: https://doi.org/10.1093/hmg/ddv360, doi:10.1093/hmg/ddv360. This article has 70 citations and is from a domain leading peer-reviewed journal.

  3. (borgese2021thelinkbetween pages 1-2): Nica Borgese, Nicola Iacomino, Sara Francesca Colombo, and Francesca Navone. The link between vapb loss of function and amyotrophic lateral sclerosis. Cells, 10:1865, Jul 2021. URL: https://doi.org/10.3390/cells10081865, doi:10.3390/cells10081865. This article has 56 citations.

  4. (murage2023characterisationofa pages 30-33): Brenda Murage. Characterisation of a model of als8 in the rat. Jan 2023. URL: https://doi.org/10.7488/era/2973, doi:10.7488/era/2973. This article has 0 citations.

  5. (borgese2021thelinkbetween pages 7-9): Nica Borgese, Nicola Iacomino, Sara Francesca Colombo, and Francesca Navone. The link between vapb loss of function and amyotrophic lateral sclerosis. Cells, 10:1865, Jul 2021. URL: https://doi.org/10.3390/cells10081865, doi:10.3390/cells10081865. This article has 56 citations.

  6. (borgese2021thelinkbetween pages 21-22): Nica Borgese, Nicola Iacomino, Sara Francesca Colombo, and Francesca Navone. The link between vapb loss of function and amyotrophic lateral sclerosis. Cells, 10:1865, Jul 2021. URL: https://doi.org/10.3390/cells10081865, doi:10.3390/cells10081865. This article has 56 citations.

  7. (larroquette2015vapbamyotrophiclateralsclerosis pages 14-15): Frédérique Larroquette, Lesley Seto, Perrine L. Gaub, Brishna Kamal, Deeann Wallis, Roxanne Larivière, Joanne Vallée, Richard Robitaille, and Hiroshi Tsuda. Vapb/amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying er stress and autophagic response. Human molecular genetics, 24 22:6515-29, Sep 2015. URL: https://doi.org/10.1093/hmg/ddv360, doi:10.1093/hmg/ddv360. This article has 70 citations and is from a domain leading peer-reviewed journal.

  8. (larroquette2015vapbamyotrophiclateralsclerosis pages 7-9): Frédérique Larroquette, Lesley Seto, Perrine L. Gaub, Brishna Kamal, Deeann Wallis, Roxanne Larivière, Joanne Vallée, Richard Robitaille, and Hiroshi Tsuda. Vapb/amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying er stress and autophagic response. Human molecular genetics, 24 22:6515-29, Sep 2015. URL: https://doi.org/10.1093/hmg/ddv360, doi:10.1093/hmg/ddv360. This article has 70 citations and is from a domain leading peer-reviewed journal.

  9. (larroquette2015vapbamyotrophiclateralsclerosis pages 10-12): Frédérique Larroquette, Lesley Seto, Perrine L. Gaub, Brishna Kamal, Deeann Wallis, Roxanne Larivière, Joanne Vallée, Richard Robitaille, and Hiroshi Tsuda. Vapb/amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying er stress and autophagic response. Human molecular genetics, 24 22:6515-29, Sep 2015. URL: https://doi.org/10.1093/hmg/ddv360, doi:10.1093/hmg/ddv360. This article has 70 citations and is from a domain leading peer-reviewed journal.

  10. (larroquette2015vapbamyotrophiclateralsclerosis pages 9-10): Frédérique Larroquette, Lesley Seto, Perrine L. Gaub, Brishna Kamal, Deeann Wallis, Roxanne Larivière, Joanne Vallée, Richard Robitaille, and Hiroshi Tsuda. Vapb/amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying er stress and autophagic response. Human molecular genetics, 24 22:6515-29, Sep 2015. URL: https://doi.org/10.1093/hmg/ddv360, doi:10.1093/hmg/ddv360. This article has 70 citations and is from a domain leading peer-reviewed journal.

  11. (larroquette2015vapbamyotrophiclateralsclerosis pages 15-17): Frédérique Larroquette, Lesley Seto, Perrine L. Gaub, Brishna Kamal, Deeann Wallis, Roxanne Larivière, Joanne Vallée, Richard Robitaille, and Hiroshi Tsuda. Vapb/amyotrophic lateral sclerosis 8 knock-in mice display slowly progressive motor behavior defects accompanying er stress and autophagic response. Human molecular genetics, 24 22:6515-29, Sep 2015. URL: https://doi.org/10.1093/hmg/ddv360, doi:10.1093/hmg/ddv360. This article has 70 citations and is from a domain leading peer-reviewed journal.

  12. (landry2026investigationsofals pages 146-153): C Landry. Investigations of als pathogenesis reveal convergent mitochondrial dysfunction and divergent integrated stress response outcomes. Unknown journal, 2026.

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