Charcot-Marie-Tooth Disease Axonal Type 2P (CMT2P) — Comprehensive Disease Characteristics Report

Disease: Charcot-Marie-Tooth Disease, Axonal, Type 2P OMIM: #614436 | Gene: LRSAM1 (chr9q33.3) | Category: Mendelian Suggested MONDO: MONDO:0013749 (Charcot-Marie-Tooth disease, axonal, type 2P)

Evidence base: literature-derived (human clinical, in vitro/biochemical, model organism, and computational). No primary datasets were provided; all claims are supported by primary literature (PMIDs) and standard disease/gene databases.

Summary

Charcot-Marie-Tooth disease axonal type 2P (CMT2P; OMIM #614436) is a rare, genetically defined form of hereditary axonal sensorimotor peripheral neuropathy caused by pathogenic variants in LRSAM1, a gene on chromosome 9q33.3 encoding a RING-type E3 ubiquitin-protein ligase. It is a member of the large, clinically and genetically heterogeneous Charcot-Marie-Tooth (CMT) family — the most common inherited neuromuscular disorder, affecting roughly 1 in 2,500 people worldwide — but CMT2P itself is one of the rarer axonal (type 2) subtypes. The disease is distinguished by a late/adult onset (typically second to fifth decade), slow progression, lower-limb predominance, frequent neuropathic pain, and marked phenotypic variability that includes asymptomatic mutation carriers.

The molecular pathology centers on loss of LRSAM1 ubiquitin ligase activity. Pathogenic variants cluster in the C-terminal RING domain that mediates the essential E2–E3 interaction required for transferring ubiquitin to substrate proteins (the best-validated target being TSG101, a component of the ESCRT endosomal-trafficking machinery). CMT2P displays a distinctive dual inheritance pattern: recessive alleles that trigger complete loss of protein (e.g., via nonsense-mediated decay, NMD) versus dominant alleles that escape NMD and produce a truncated protein exerting a dominant-negative effect on the RING domain. Whether a 3′-located premature-termination variant escapes or triggers NMD effectively determines whether disease is dominant or recessive — a rare and instructive example of a single gene where variant position dictates inheritance mode.

There is no curative therapy; management is entirely symptomatic and supportive (ankle-foot orthoses, physical/occupational therapy, foot-deformity surgery, neuropathic pain control, and genetic counseling), and life expectancy is normal. An emerging and biologically intriguing finding is that LRSAM1 disease may extend beyond the peripheral nervous system: within the original dominant kindred, several affected members developed late-onset parkinsonism, and additional cases pair CMT2P with parkinsonian features — linking this peripheral neuropathy to a central nervous system phenotype and to ubiquitin-proteostasis themes shared with neurodegeneration.

1. Disease Information

Overview. CMT2P is an axonal (as opposed to demyelinating) hereditary motor and sensory neuropathy. Clinically it presents as a length-dependent, distal, symmetric sensorimotor polyneuropathy with distal weakness and atrophy (legs > arms), distal sensory loss, reduced/absent tendon reflexes, foot deformity (pes cavus), and gait impairment — the classic CMT phenotype — but with a characteristically mild, late-onset, slowly progressive course.

Key identifiers:

Synonyms / alternative names: CMT2P; Charcot-Marie-Tooth disease, axonal, type 2P; CMT2G (a historically separate entity now reclassified as CMT2P after identification of the LRSAM1 p.Cys694Tyr mutation — PMID: 27686364); LRSAM1-related Charcot-Marie-Tooth disease.

Information source type. The knowledge base for CMT2P is derived overwhelmingly from aggregated disease-level resources — OMIM, published family/pedigree studies, and case reports — rather than large EHR cohorts, reflecting its rarity.

2. Etiology

Primary cause — genetic. CMT2P is a monogenic Mendelian disorder caused by pathogenic variants in LRSAM1. The first description came from Guernsey et al. (2010) who used homozygosity mapping in a large recessive eastern Canadian kindred (locus chr9:122–129 Mb) and identified a homozygous intronic splice-acceptor variant (AG→AA) producing a frameshift/truncation and complete loss of protein (PMID: 20865121). Weterman et al. (2012) then identified a dominant frameshift, p.Leu708Argfs*28, in the C-terminal RING domain in a three-generation family with a strong LOD score of 5.12 (PMID: 22012984).

"A homozygous pathogenic variant was identified in the gene encoding leucine rich repeat and sterile alpha motif 1 (LRSAM1) by direct DNA sequencing" — Guernsey et al., PMID: 20865121

"This frameshift mutation (p.Leu708Argfx28) is located in the C-terminal RING finger motif of the encoded protein." — Weterman et al., PMID: 22012984

Genetic risk factors. The causal variants themselves are the risk factors; no additional susceptibility loci are established. Modifier considerations: in a family co-segregating a RAB7A (CMT2B) mutation and a novel LRSAM1 variant, gender and possible RAB7A/LRSAM1 gene interactions were proposed to explain marked variability in age of onset (PMID: 27462242).

Environmental risk / protective factors. No environmental risk or protective factors are established for CMT2P in humans. However, an important gene–environment interaction was demonstrated in the mouse model: Lrsam1 mutant mice are hypersensitive to the axonal neurotoxin acrylamide, indicating that loss of LRSAM1 lowers the axonal threshold for degeneration under toxic stress (PMID: 23519028). This suggests that, mechanistically, neurotoxic exposures could plausibly aggravate an LRSAM1-compromised nervous system, though this has not been shown clinically.

Genetic protective factors. None specifically identified. Incomplete penetrance/asymptomatic carriers imply the existence of unknown modifiers, but none have been mapped.

3. Phenotypes

CMT2P phenotypes are those of a distal, length-dependent axonal sensorimotor polyneuropathy. Onset is typically adult/late (2nd–5th decade), severity is mild to moderate, progression is slow and progressive, and there is variable expressivity including asymptomatic carriers (PMID: 33568173, PMID: 33414056).

"dominant CMT2P is usually characterized by relatively mild, slowly progressive axonal neuropathy, mainly involving lower limbs, with age of onset between the second and fifth decades of life" — Palaima et al., PMID: 33568173

"CMT2P is a rare, but nevertheless relevant cause of adult-onset axonal and painful neuropathy" — Reilich et al., PMID: 33414056

Quality-of-life impact. As with CMT broadly, the dominant burden is on mobility and gait, with foot deformity, falls risk, and — distinctively for CMT2P — chronic neuropathic pain. Supportive care (orthotics, rehabilitation) improves quality of life (PMID: 40014417, PMID: 40636623). Formal EQ-5D/SF-36/PROMIS data specific to CMT2P are not available.

4. Genetic / Molecular Information

Causal gene. LRSAM1 (Leucine Rich Repeat And Sterile Alpha Motif containing 1; also called Tal), HGNC:25135, gene OMIM 610933, NCBI Gene 90678, UniProt Q6UWE0, on chromosome 9q33.3. It encodes a universally expressed RING-type E3 ubiquitin-protein ligase with domain architecture LRR – coiled-coil – SAM – PDZ-binding – RING (PMID: 33568173, PMID: 23245322).

Pathogenic variants cluster in the 3′-prime exons encoding the C-terminal RING domain. Reilich et al. (2021) reported 14 patients from 12 families harboring 10 different LRSAM1 variants (7 novel), predominantly dominant (PMID: 33414056).

Variant classification (ACMG/AMP). Interpretation is challenging precisely because pathogenic variants cluster at the 3′ end where premature-termination codons may or may not escape NMD; careful application of PVS1 and related criteria is required depending on exact position and predicted NMD outcome (PMID: 33414056).

"Variants at the 3`end may or may not escape from nonsense-mediated decay, thereby defining the pattern of inheritance" — Reilich et al., PMID: 33414056

"clustering of pathogenic variants in 3´-prime exons, interpretation of genetic variants in LRSAM1 is challenging" — Reilich et al., PMID: 33414056

Functional consequences. - Recessive variants → complete loss of LRSAM1 protein → loss of function. - Dominant variants → truncated RING-domain protein escaping NMD → dominant-negative effect on ligase activity (PMID: 33414056).

"the C-terminal RING domain, which exerts a dominant-negative effect on protein function, whenever affected by an altered or truncated protein" — Reilich et al., PMID: 33414056

Allele frequency / somatic vs germline. All disease variants are germline and rare (not established as recurrent population polymorphisms); LRSAM1 mutations are considered rare even within CMT2 (PMID: 28335037). No somatic (COSMIC/cancer) role is relevant.

Modifier genes / epigenetics / chromosomal abnormalities. Possible RAB7A × LRSAM1 interaction and a gender effect were proposed as phenotype modifiers (PMID: 27462242). No epigenetic mechanisms or large chromosomal abnormalities are implicated; transcriptomic changes (upregulation of NEDD4L and TNFRSF21) were seen with the p.Cys694Tyr mutation (PMID: 27686364).

5. Environmental Information

No environmental, lifestyle, or infectious agents cause CMT2P — it is a purely genetic disorder. The only mechanistically relevant environmental link is experimental: LRSAM1-deficient mouse axons are more sensitive to the neurotoxin acrylamide (PMID: 23519028), raising the theoretical possibility that neurotoxic exposures could exacerbate axonal vulnerability. Of interest to the protein's normal biology, LRSAM1 participates in anti-bacterial autophagy (xenophagy) of intracellular Salmonella Typhimurium (PMID: 23245322), but there is no evidence infection triggers the neuropathy.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

1. A germline pathogenic variant arises in LRSAM1, clustered in the 3′ exons encoding the C-terminal RING domain.
2. Depending on variant position and NMD, this leads to one of two states:
3. (Recessive branch) biallelic loss → NMD/complete absence of LRSAM1 protein → total loss of E3 ligase function; or
4. (Dominant branch) a truncated protein that escapes NMD → a dominant-negative RING-domain protein that poisons residual ligase activity.
5. Either state results in disrupted E2–E3 interaction, the essential step for transferring ubiquitin from the E2 conjugating enzyme to substrates — thereby abrogating LRSAM1-mediated ubiquitylation (PMID: 28335037).
6. Loss of ubiquitylation of the validated target TSG101 (an ESCRT-I component) impairs endosomal sorting / multivesicular-body (MVB) trafficking and receptor endocytosis (PMID: 15256501) — inferred to perturb membrane/protein homeostasis in neurons.
7. Impaired proteostasis and trafficking lowers the threshold for length-dependent distal axonal degeneration — demonstrated indirectly by heightened axonal vulnerability to neurotoxic stress in the mouse model (PMID: 23519028).
8. Degeneration of the longest peripheral motor and sensory axons produces distal muscle weakness/atrophy, distal sensory loss, neuropathic pain, areflexia, pes cavus, and gait impairment — the CMT2P phenotype.
9. (Branch — CNS extension, inferred) In some individuals the same ligase dysfunction is associated with later degeneration affecting the substantia nigra, manifesting as late-onset parkinsonism (PMID: 26900582, PMID: 40721190); the mechanism connecting LRSAM1 to nigral neurons remains undefined.

Causal chain diagram

LRSAM1 pathogenic variant (3' RING-encoding exons, chr9q33.3)
              |
 ┌────────────────────┴────────────────────┐
   (recessive)                                (dominant)
 biallelic, NMD →                       PTC escapes NMD →
 complete loss of LRSAM1               truncated RING protein
|                                        |
└───────────────┬────────────────────────┘
        v
Disrupted E2–E3 interaction  →  loss of ubiquitylation activity
        v
     ↓ Ubiquitination of TSG101 (ESCRT-I)  →  impaired endosomal/MVB trafficking
        v
     Perturbed neuronal proteostasis & membrane homeostasis (inferred)
        v
     ↑ Vulnerability to length-dependent DISTAL AXON DEGENERATION
       (mouse: unmasked by neurotoxic stress; ↑TNFRSF21)
        v
   ┌────────────────────┴──────────────────────────┐
   v                                                v
 PNS phenotype:                          CNS extension (some patients):
 distal weakness, sensory loss,          late-onset parkinsonism
 neuropathic pain, pes cavus,            (substantia nigra; mechanism unknown)
 areflexia, gait impairment

Supporting detail

• Molecular pathway / biochemical defect. The core lesion is in the ubiquitin–proteasome / ubiquitin-conjugation pathway. LRSAM1 is a RING E3 ligase; RING-domain variants cause "loss of the E2-E3 interaction that is an essential prerequisite for supporting ubiquitylation of target substrates" (PMID: 28335037).
• Protein function. Two functional modules: the LRR domain targets substrates (e.g., cytosolic bacteria) and the RING domain catalyzes ubiquitin transfer — "these functions require LRSAM1's leucine-rich repeat and RING domains, respectively" (PMID: 23245322).
• Cellular processes. Endosomal/ESCRT trafficking, MVB and retrovirus budding (via TSG101 monoubiquitination, PMID: 15256501); autophagy/xenophagy; and, downstream, axon degeneration. Transcriptomic profiling of patient cells implicated TNFRSF21 (a regulator of axonal degeneration) and pathways shared with ALS and Alzheimer disease (PMID: 27686364).
• Subcellular localization. In transfected cells LRSAM1 localizes to a perinuclear compartment just beyond the Golgi (PMID: 23519028).

Upstream vs downstream: the mutation and lost ubiquitylation are upstream; trafficking/proteostasis defects are intermediate; distal axonal degeneration and clinical signs are downstream.

Suggested ontology terms. GO:0016567 (protein ubiquitination), GO:0004842 (ubiquitin-protein transferase activity), GO:0061630 (ubiquitin protein ligase activity), GO:0007032 (endosome organization), GO:0098930 (axonal transport), GO:0006914 (autophagy). Cell types (CL): CL:0000101 (sensory neuron), CL:0000100 (motor neuron), CL:0002573 (Schwann cell). Cellular components: GO:0005768 (endosome), GO:0000813 (ESCRT-I complex), GO:0005794 (Golgi apparatus).

7. Anatomical Structures Affected

Organ / system level. The peripheral nervous system is primary (UBERON:0000010). Body system: nervous system (UBERON:0001016). Secondary/musculoskeletal involvement includes distal limb muscles and the foot/skeleton (pes cavus, foot deformity); CMT patients also show an under-recognized rate of hip acetabular dysplasia (21% of imaged CMT patients in one series — PMID: 40432997). The emerging CNS extension implicates the substantia nigra / basal ganglia (PMID: 26900582).

Tissue / cell level. Nervous tissue — peripheral motor and sensory axons; LRSAM1 is abundantly expressed in PNS motor and sensory neurons (PMID: 23519028). Affected cells: motor neurons (CL:0000100) and sensory neurons (CL:0000101); skeletal muscle secondarily denervated (CL:0000188).

Subcellular level. Endosome/MVB (GO:0005768), ESCRT-I complex (GO:0000813), Golgi-adjacent perinuclear compartment (GO:0005794).

Localization. Distal, length-dependent, bilateral and symmetric, lower limbs > upper limbs. Suggested UBERON: UBERON:0001322 (sciatic nerve) and distal peroneal/tibial nerve territory; spinal cord and CNS not primarily affected in the classic peripheral phenotype.

8. Temporal Development

• Onset: adult/late, typically 2nd to 5th decade; insidious/chronic (PMID: 33568173). A rare early-onset autosomal dominant family has been reported (PMID: 38330802).
• Progression: slow and progressive; generally mild ("quiescent") axonal neuropathy (PMID: 27686364).
• Course pattern: chronic, lifelong, non-remitting, non-episodic.
• Critical periods / CNS window: late-onset parkinsonism appears years after neuropathy onset (ages ~50–65) in some patients (PMID: 26900582).

9. Inheritance and Population

Epidemiology. CMT overall affects ~1:2,500 worldwide with >100 known genetic causes (PMID: 40219666). CMT2P is a rare subtype; LRSAM1 mutations are uncommon even within CMT2 (PMID: 28335037). Precise CMT2P prevalence/incidence are not established.

"Affecting about ~1:2,500 people worldwide, CMT has over 100 known genetic causes, leading to different subtypes with varying disease severity and progression." — Stavrou et al., PMID: 40219666

Inheritance. Both autosomal dominant (predominant) and autosomal recessive, determined by variant location and NMD outcome (see Section 4). Dominant = dominant-negative RING variants escaping NMD; recessive = biallelic complete loss (PMID: 33414056).

Penetrance / expressivity. Incomplete penetrance and variable expressivity, including asymptomatic carriers detectable only by lower-limb muscle MRI (PMID: 27686364, PMID: 33568173).

Founder effects / consanguinity. The original recessive kindred was a large consanguineous eastern Canadian family (homozygous founder-type splice variant) (PMID: 20865121). Carrier status for the recessive LRSAM1 allele has been incidentally detected in idiopathic neuropathy cohorts (PMID: 39290488).

Demographics. No strong ethnic predilection; reported families span Canada, the Netherlands, and others. Sex ratio not clearly skewed, though gender was proposed as a modifier in one family (PMID: 27462242). Genetic anticipation and germline mosaicism are not established.

10. Diagnostics

Clinical / electrophysiology. Diagnosis rests on nerve conduction studies / EMG demonstrating an axonal (rather than demyelinating) sensorimotor neuropathy: reduced amplitudes with relatively preserved conduction velocities (PMID: 40721190). Clinical exam shows distal weakness, sensory loss, areflexia, pes cavus.

Imaging. MRI of lower-limb musculature systematically reveals fatty atrophy in both clinical and subclinical carriers and is useful to detect minimal/subclinical disease (PMID: 27686364).

Genetic testing (definitive). Diagnosis is confirmed by identifying a pathogenic LRSAM1 variant. Recommended approach: multigene neuropathy/CMT panel or exome sequencing, given the >100 CMT genes; targeted LRSAM1 analysis when phenotype/family history suggests it. LRSAM1 is included on inherited neuromuscular gene panels (PMID: 39290488). Careful ACMG interpretation of 3′ PTC variants (NMD escape) is essential (PMID: 33414056). Chromosomal microarray, karyotyping, FISH, mitochondrial and repeat-expansion testing are not relevant to CMT2P.

Omics diagnostics. Not standard; research transcriptome profiling of patient lymphoblasts has shown disease-associated expression changes (PMID: 27686364).

Differential diagnosis. Other axonal CMT2 subtypes (CMT2A/MFN2, CMT2B/RAB7A, CMT2K/GDAP1, etc.), hereditary transthyretin (ATTRv) amyloidosis (important treatable mimic — PMID: 39290488), CMT1 (demyelinating; PMP22), acquired/idiopathic axonal polyneuropathies, and ALS5/SPG11 overlap syndromes (PMID: 26556829).

Screening. Cascade genetic testing of at-risk relatives once a familial variant is known; no population newborn screening.

11. Outcome / Prognosis

• Survival / life expectancy: normal. CMT2P is not life-limiting; by analogy to other CMT the disease "reflects a process of normal ageing" with normal life expectancy (PMID: 24646194).
• Morbidity / disability. Chronic, slowly progressive mobility impairment, foot deformity, falls risk, and neuropathic pain dominate; wheelchair dependence is uncommon given the mild course.
• Complications. Foot deformities requiring surgery; possible hip acetabular dysplasia in CMT broadly (PMID: 40432997); late-onset parkinsonism as a distinct CNS complication in some LRSAM1 patients (PMID: 26900582).
• Prognostic factors. Variant type/inheritance (dominant-negative vs LOF), and modifiers such as gender/second-gene interaction (PMID: 27462242). No validated molecular prognostic biomarkers.

12. Treatment

No curative therapy exists; management is symptomatic and supportive.

"Currently, no curative treatment exists for CMT. Management focuses on symptomatic interventions, including orthotic support, surgical procedures, and physical therapy." — Kikuchi, PMID: 40636623

Experimental / disease-modifying (CMT broadly, not LRSAM1-specific). No approved disease-modifying drug for CMT2P. Across CMT, gene therapy (silencing/replacement/editing via AAV vectors) is under active preclinical/early-clinical development but faces blood–nerve/brain-barrier delivery, immunogenicity, and scalability challenges (PMID: 40219666). Other emerging approaches include PMP22 silencers (for CMT1A), HDAC6 inhibitors, and govorestat (aldose reductase inhibitor, CMT-SORD trial) — none specific to LRSAM1 (PMID: 40014417).

"Currently, there are no approved treatments and care focuses on managing symptoms." — Stavrou et al., PMID: 40219666

Pharmacogenomics / personalized medicine. No LRSAM1-specific pharmacogenomic guidance. The dual LOF-vs-dominant-negative mechanism implies different rational strategies (gene replacement for recessive LOF; allele-specific silencing for dominant-negative alleles) — currently conceptual.

13. Prevention

CMT2P cannot be prevented (genetic). Prevention is limited to reproductive/genetic risk management and complication avoidance:

• Primary: Genetic counseling, carrier/cascade testing, and reproductive options (prenatal testing, preimplantation genetic diagnosis) for known familial variants (general CMT precedent — PMID: 24646194).
• Secondary: Early detection of subclinical carriers via lower-limb muscle MRI (PMID: 27686364); early physiotherapy/orthotics.
• Tertiary: Prevent complications — orthotic support to prevent falls/deformity progression, monitoring for hip dysplasia and, given the emerging link, parkinsonian features.
• Behavioral: Theoretical avoidance of neurotoxic exposures (extrapolated from acrylamide sensitivity in the mouse model, PMID: 23519028) — not a clinical guideline.

No immunization, public-health, or infectious-control measures apply.

14. Other Species / Natural Disease

• Model species: Mus musculus (NCBI Taxon 10090) — the Lrsam1 mutant mouse (PMID: 23519028).
• Orthologous gene: mouse Lrsam1, abundantly expressed in PNS motor and sensory neurons.
• Natural disease in companion animals/wildlife: No naturally occurring LRSAM1/CMT2P disease documented in other species (OMIA); the LRR–RING E3-ligase function is evolutionarily conserved, and the protein's ubiquitin-dependent xenophagy role is conserved across mammalian cells (PMID: 23245322).
• Zoonotic potential: None (non-infectious genetic disease).

15. Model Organisms

Mouse (Lrsam1 mutant). The principal model (PMID: 23519028):

• Phenotype recapitulation (partial): Both homozygous and heterozygous mice have largely normal neuromuscular performance and only very mild age-related neuropathy — milder than the human disease.
• Key finding — sensitized axons: mutant axons are hypersensitive to axonal neurotoxin challenge.

"Lrsam1 mutant mice are more sensitive to challenge with acrylamide, a neurotoxic agent that causes axon degeneration, indicating that the axons in the mutant mice are indeed compromised" — Bogdanik et al., PMID: 23519028

• Localization insight: LRSAM1 localizes to a perinuclear post-Golgi compartment, with little colocalization with endosome-to-lysosome trafficking machinery.
• Limitations: Mild phenotype limits modeling of overt human neuropathy; does not capture dominant-negative human biology or the parkinsonism extension.
• Cellular / in vitro models: Patient lymphoblasts/fibroblasts for ubiquitylation assays and transcriptomics (PMID: 28335037, PMID: 27686364); in vitro ubiquitylation reconstitution to test E2–E3 interaction defects.
• Resources: MGI (mouse) and standard CMT model repositories.

Mechanistic Model / Interpretation

The unifying theme is failure of a RING E3 ubiquitin ligase, converging on impaired proteostasis and endosomal trafficking in neurons. CMT2P is mechanistically distinctive within CMT2 for two reasons: (a) its position-dependent dual inheritance, in which NMD escape/triggering of a 3′ premature-termination codon decides whether disease is dominant (dominant-negative) or recessive (complete loss of function); and (b) a dominant-negative mode operating for most disease alleles. The recurrent link to parkinsonism situates LRSAM1 within broader ubiquitin-proteostasis neurodegeneration biology — echoed by patient-cell transcriptomes sharing pathways with ALS and Alzheimer disease — and suggests the same ligase defect can, over decades, extend from the longest peripheral axons to vulnerable central (nigral) neurons.

Evidence Base

Evidence source types: human clinical/genetic (family & cohort studies, reviews), model organism (mouse), and in vitro/biochemical (ubiquitylation assays, cell transfection).

Limitations and Knowledge Gaps

1. Rarity limits epidemiology. No reliable prevalence/incidence, sex ratio, or natural-history quantitation specific to CMT2P; most data come from individual pedigrees and case reports.
2. Substrate biology is incomplete. TSG101 is the only well-validated LRSAM1 ubiquitylation target relevant to disease; how impaired TSG101/ESCRT function specifically drives axonal degeneration is inferred, not demonstrated.
3. Genotype–phenotype uncertainty. NMD escape/dominant-negative predictions for 3′ PTC variants are not always experimentally verified, complicating ACMG classification.
4. Mouse model is mild. The Lrsam1 mouse under-recapitulates overt human neuropathy and does not model the dominant-negative or parkinsonism aspects.
5. The parkinsonism link is preliminary. Based on one family plus isolated cases; causality, penetrance, and mechanism (LRSAM1 in substantia nigra) are unknown.
6. No disease-specific therapy or biomarkers. All treatments are symptomatic; no validated prognostic molecular markers.

Proposed Follow-up Experiments / Actions

1. Functional NMD/dominant-negative assays for each reported 3′ LRSAM1 PTC variant (patient RNA + minigene assays) to firm up ACMG calls and inheritance prediction.
2. iPSC-derived motor/sensory neurons carrying dominant-negative vs LOF LRSAM1 alleles to test axonal degeneration, ESCRT/TSG101 trafficking, and stress vulnerability — bridging the mild mouse-model gap.
3. Expand substrate mapping (ubiquitylation proteomics) in neurons to identify axon-relevant LRSAM1 targets beyond TSG101.
4. Systematic ascertainment of parkinsonism/CNS features across LRSAM1 cohorts (DAT-SPECT imaging, longitudinal follow-up) to establish frequency, penetrance, and mechanism of the CNS extension.
5. Allele-specific silencing (dominant alleles) and gene replacement (recessive LOF) proof-of-concept in cellular/mouse models, leveraging the AAV gene-therapy platforms being developed for CMT broadly.
6. Registry-based natural history study to define CMT2P prevalence, progression rate, and disability trajectory, enabling future trial readiness.
7. Test neurotoxic-exposure interaction clinically/epidemiologically, motivated by acrylamide hypersensitivity in the mouse model.

Report compiled from an autonomous multi-iteration literature investigation (8 confirmed findings, 21 papers reviewed). Evidence is predominantly human genetic/clinical and model-organism; CMT2P remains a rare, symptomatically managed axonal neuropathy with an emerging CNS dimension.

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Term Validation

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Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

• MONDO:0013749 (2 mentions) - the report calls it "Charcot-Marie-Tooth disease, axonal, type 2P", "Suggested MONDO"; MONDO calls it ventricular septal defect 3
• HP:0001761 (1 mention) - the report calls it "Physical manifestation"; HP calls it Pes cavus
• HP:0009027 (1 mention) - the report calls it "Clinical sign"; HP calls it Foot dorsiflexor weakness
• NCIT:C15224 (1 mention) - the report calls it "pain management"; NCIT calls it Nutrition Research, Fats
• NCIT:C15633 (1 mention) - the report calls it "genetic counseling"; NCIT calls it Cancer Pain Management

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• NCIT:C50008 (1 mention) - the report calls it "orthotic device"; NCIT calls it Interface Device
• NCIT:C15327 (1 mention) - the report calls it "physical therapy"; NCIT calls it Lumbar Puncture, and lists "Spinal Tap" among its other names

Terms named inconsistently

The report gives these identifiers more than one name of its own:

• MONDO:0013749 - called "Charcot-Marie-Tooth disease, axonal, type 2P", "Suggested MONDO"