Charcot-Marie-Tooth Disease Axonal Type 2C (CMT2C) — Comprehensive Research Report

1. Disease Information

Overview: Charcot-Marie-Tooth disease axonal type 2C (CMT2C), also designated Hereditary Motor and Sensory Neuropathy type IIC (HMSN2C), is an autosomal dominant, motor-predominant, non-length-dependent peripheral neuropathy or motor neuronopathy caused by heterozygous gain-of-function mutations in TRPV4. It is one of three clinically recognized autosomal dominant "TRPV4 neuromuscular disorders" — alongside scapuloperoneal spinal muscular atrophy (SPSMA) and congenital distal spinal muscular atrophy (CDSMA/CSMA) — which together with a family of TRPV4 skeletal dysplasias constitute the broader "TRPV4-pathy" spectrum (GeneReviews: Autosomal Dominant TRPV4-Related Disorders; Nature Genetics 2010, ng.512; J Hum Genet 2010, jhg201037).

Key identifiers: - OMIM: #606071 — Hereditary Motor and Sensory Neuropathy, Type IIC (HMSN2C) (OMIM 606071); the TRPV4 gene entry is OMIM 605427 (OMIM 605427) - Orphanet: ORPHA:99937 — "Autosomal dominant Charcot-Marie-Tooth disease type 2C" (Orphanet 99937) - MONDO/MedGen: MedGen concept C1853710 (MedGen 342947; GARD) - Gene: TRPV4 (transient receptor potential cation channel subfamily V member 4), chromosome 12q24.11 - Allelic disorders (same gene, different phenotype "bin"):* Scapuloperoneal spinal muscular atrophy (SPSMA, OMIM 181405), congenital distal spinal muscular atrophy (CDSMA/HMND8, OMIM 600175), and a family of TRPV4 skeletal dysplasias (metatropic dysplasia, spondylometaphyseal dysplasia Kozlowski type, brachyolmia, parastremmatic dysplasia)

Synonyms: HMSN2C; CMT2C; hereditary motor and sensory neuropathy type 2C; TRPV4-related axonal neuropathy; CMT2C with vocal cord paresis.

Evidence basis: This is an aggregated disease-level entity, not derived from a single EHR cohort. Curation rests on published case series/family pedigrees, a small number of dedicated CMT2 patient cohorts (USA, European, Australian), the OMIM/Orphanet/GeneReviews synthetic entries, and mechanistic cell/animal-model studies — not large-scale registry or claims data.

2. Etiology

Primary cause: CMT2C is caused entirely by heterozygous, dominantly acting, gain-of-ion-channel-function missense variants in TRPV4 (Deng et al., Nat Genet 2010;42:165–169; Landouré et al., Nat Genet 2010, ng.512). It is a monogenic Mendelian disorder — there is no evidence for polygenic, infectious, or purely environmental causation of the core neuropathy phenotype.

Genetic risk factors: - Causal variants cluster on "the highly positively charged convex surface of the ankyrin repeat domain," targeting strictly conserved arginine residues in three consecutive finger loops of the protein (GeneReviews NBK201366). - Well-validated recurrent pathogenic variants: p.Arg186Gln, p.Arg232Cys, p.Arg269Cys, p.Arg269His, p.Arg315Trp, p.Arg316Cys, p.Arg316His (GeneReviews NBK201366). The founding CMT2C family carried c.806G>A (p.Arg269His) (Deng et al. 2010); another kindred with the founding phenotype carried the paralogous c.805C>T/c.806G>A → R269C/R269H substitutions at the same residue (review, PMC10311707). - Modifier/severity determinants: the same residue can produce markedly different severity; "the degree of baseline calcium elevation correlates with development of mixed [neuropathy + skeletal] phenotypes and sensitivity to pharmacologic channel inhibition" (Nishida/Zhu et al., PMC8935273). No independent trans-acting modifier gene has been established for the neuromuscular phenotype. - Reduced penetrance and highly variable expressivity are intrinsic features — the specific subtype (CMT2C vs. SPSMA vs. CDSMA), age of onset, and severity "cannot be accurately predicted" from genotype alone (GeneReviews NBK201366).

Environmental/lifestyle risk factors: None specific to disease causation are documented (this is a fully penetrant-genotype, non-environmentally-triggered channelopathy). However, several environmental/physiologic exposures exacerbate manifestations in carriers: - Obesity worsens ambulation (GeneReviews NBK201366) - Upper respiratory tract infections can precipitate acute worsening of vocal-fold/airway obstruction via laryngeal edema (GeneReviews NBK201366) - Neurotoxic medications (standard CMT avoid-list) can accelerate neuropathy - Pregnancy: ~50% of women with CMT report increased weakness during pregnancy, typically resolving postpartum; CMT pregnancies show higher rates of placenta previa, abnormal fetal presentation, and preterm delivery, though overall neonatal outcomes are comparable to background populations (GeneReviews NBK201366)

Protective factors: No genetic or environmental protective factors are described in the literature for TRPV4 neuromuscular disease; this contrasts with skeletal-dysplasia TRPV4 alleles, where no protective variants are documented either.

Gene-environment interaction: Not a recognized feature of this disorder; the driving mechanism is cell-autonomous/vascular channel gain-of-function rather than an environmentally modulated genetic susceptibility.

3. Phenotypes

CMT2C exists on a phenotypic continuum with SPSMA and CDSMA. Core features (with suggested HPO terms):

Onset: Highly variable — "usually between early childhood and age 25 years," but documented range is birth to after the 8th decade; some carriers have subtle findings that escape clinical recognition entirely (reduced penetrance) (GeneReviews NBK201366). Course is chronic/progressive in most, but severity and rate vary widely even within one family carrying the identical variant.

Severity/progression: "There is a wide range of phenotypic severity; in the mildest of the autosomal dominant TRPV4-related disorders life span is normal, whereas in the most severe it is shortened" (GeneReviews NBK201366). Suggestive "red flag" combination for clinicians: vocal cord paralysis + scapular weakness/wasting + skeletal dysplasia + hearing loss in a CMT2 patient (Neurology 2015, Neurology 2014 WNL.0000000000000450; NeuroMolecular Medicine 2019).

Quality of life: No CMT2C-specific EQ-5D/SF-36 data were identified; general CMT registry literature documents mobility impairment, orthotic/AFO dependence, and — distinctively for this subtype — impact from laryngeal dysfunction (dysphonia, aspiration risk, airway obstruction) and respiratory limitation, which are less prominent in typical demyelinating/axonal CMT.

4. Genetic/Molecular Information

Causal gene: TRPV4 (HGNC:17728, chr12q24.11); OMIM gene entry *605427.

Variant classification/type: Exclusively missense (with rare splice-site variants reported in ClinVar, e.g., c.2209-5C>T); no whole-gene deletions/duplications have been reported for the autosomal dominant neuromuscular phenotype, and sequence analysis alone identifies essentially 100% of currently known pathogenic variants (GeneReviews NBK201366). ClinVar lists numerous variant-specific submissions explicitly annotated "AND Charcot-Marie-Tooth disease axonal type 2C," e.g. p.Arg774Cys, p.Arg464Cys, p.Arg151Trp, p.Arg315Trp (ClinVar RCV000645535; RCV000645552; RCV000005291).

Functional consequence: Uniformly gain of channel function (not loss of function) — increased constitutive and agonist-evoked Ca²⁺ influx through the mutant channel, producing "cytotoxic hypercalcemia" (Neurology 2011, WNL.0b013e31820f2de3; PMID 21288981). Original functional work: HEK293 cells transfected with mutant TRPV4 (R269H) showed normal plasma-membrane trafficking but markedly increased constitutive and stimulus-evoked channel currents plus cellular toxicity (Deng et al. 2010; Landouré et al. 2010).

Allele frequency: These are rare, largely private, dominant disease-causing missense variants; population allele frequency in gnomAD is expected to be near-absent for pathogenic alleles (no specific carrier-frequency estimate was located in this search — flag as data gap).

Origin: Both inherited (familial, autosomal dominant transmission with 50% recurrence risk) and de novo cases occur; severe skeletal-dysplasia-end phenotypes are typically de novo in unaffected parents, while milder/classic neuromuscular phenotypes are more often inherited (GeneReviews NBK201366). No somatic/mosaic TRPV4 CMT2C cases were identified in this search.

Modifier genes: None specific and validated; phenotypic variability appears largely explained by variant position/severity of channel gain-of-function rather than a distinct modifier locus (see §2).

Structural/mechanistic basis: Cryo-EM structures of TRPV4 in complex with RhoA GTPase show that many disease residues lie at the TRPV4–RhoA interface; disrupting this interface (by mutating either partner) increases TRPV4 channel activity, drives cytoskeletal remodeling, and impairs neurite extension (Deng lab/PMC10290081; PMID 33664271). A second regulatory mechanism involves ubiquitination of intrinsically disordered N- and C-terminal cytosolic regions of TRPV4: neuropathy-causing gain-of-function mutations reduce channel ubiquitination in cellular and Drosophila models, and experimentally increasing mutant-channel ubiquitination partially suppresses channel overactivity (Aisenberg et al., J Biol Chem 2022, PMC9010760).

Epigenetics/chromosomal abnormalities: Not described as relevant to this single-gene channelopathy; no epigenetic or large chromosomal-rearrangement mechanism has been reported.

5. Environmental Information

CMT2C is not primarily environmentally caused, but relevant environmental/exposure modulators of morbidity include: - Upper respiratory infection — precipitates vocal-fold edema and can acutely worsen airway obstruction in patients with baseline vocal-fold paresis (GeneReviews NBK201366) - Neurotoxic drug exposure — standard CMT avoidance list (vincristine and other agents) can worsen underlying axonal neuropathy - Obesity — a modifiable factor worsening ambulatory function - No infectious agent is causally implicated in CMT2C itself (distinct from acquired/inflammatory neuropathies).

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

1. Molecular initiating event: Heterozygous missense variant in the ankyrin-repeat domain (or C-terminal region) of TRPV4 disrupts autoinhibitory conformational constraints, including loss of normal TRPV4–RhoA interaction and reduced channel ubiquitination/turnover (PMC10290081; PMC9010760).
2. Molecular consequence: Constitutive and stimulus-evoked gain of Ca²⁺-channel function — excess Ca²⁺ influx through the nonselective cation channel (Nat Genet 2010; Neurology 2011 PMID 21288981).
3. Cellular consequence: "Cytotoxic hypercalcemia" — sustained intracellular Ca²⁺ overload causes cytoskeletal/RhoA-pathway dysregulation, impaired neurite extension, and cell process retraction in neuronal/glial cell models (PMID 33664271).
4. Vascular/barrier consequence (new mechanistic insight, 2024): Knock-in mouse models (R269C, R232C) show that the dominant pathogenic driver is TRPV4 gain-of-function specifically in vascular endothelial cells, causing focal breakdown of the blood–spinal cord barrier (BSCB); genetic deletion of mutant Trpv4 from endothelial cells (but not neurons, glia, or muscle) rescues the motor phenotype, indicating a non-cell-autonomous, endothelial-driven mechanism of motor neuron degeneration (Chen et al., PMC11316273, PMID 38776392).
5. Tissue/organism consequence: Regional anterior horn cell/motor neuron loss, motor axon degeneration → progressive limb, laryngeal, diaphragmatic, and (in overlap cases) skeletal phenotypes.

Molecular pathways: TRPV4 calcium signaling; RhoA GTPase/cytoskeletal remodeling pathway; ubiquitin-proteasome-linked channel turnover regulation.

Cellular processes: Calcium-dependent cytotoxicity; impaired neurite outgrowth; vascular endothelial barrier dysfunction; (in the skeletal-dysplasia allelic spectrum) altered chondrocyte hypertrophic differentiation — TRPV4 skeletal-dysplasia mutations "suppress the hypertrophic differentiation of human iPSC-derived chondrocytes" (biorxiv preprint referenced in search, distinguishing the skeletal branch mechanistically from the neuromuscular branch).

Suggested ontology terms: - GO biological process: GO:0070588 (calcium ion transmembrane transport), GO:0007584 (response to nutrient — n/a), better: GO:0006816 (calcium ion transport), GO:0007015 (actin filament organization, via RhoA), GO:0007520 (myoblast fusion — n/a) - GO molecular function: GO:0005227 (calcium-activated cation channel activity), GO:0015276 (ligand-gated ion channel activity) - Cell types (CL): CL:0000540 (neuron)/CL:0011031 (spinal cord motor neuron), CL:0002139 (vascular associated smooth muscle... or) CL:0002139/CL:0000115 (endothelial cell), CL:0000499 (stromal cell — n/a)

Biochemical abnormality: Ion channel gain-of-function (not enzyme deficiency); no metabolic pathway defect is implicated.

Immune involvement: None established; this is not an inflammatory/autoimmune neuropathy.

Omics: No large-scale human transcriptomic/proteomic/metabolomic dataset specific to CMT2C patient tissue was identified in this search (data gap). Model-system transcriptomic/functional-genomics data exist chiefly in the Drosophila and mouse knock-in systems described above and in the endothelial-lineage-tracing study (PMC11316273).

7. Anatomical Structures Affected

Organ/system level: - Peripheral nervous system: motor and (secondarily) sensory peripheral nerves; anterior horn cells (motor neuronopathy component) - Larynx: vocal fold/recurrent laryngeal nerve-innervated musculature - Respiratory system: diaphragm, intercostal muscles - Auditory system: cochlea (sensorineural hearing loss) - Musculoskeletal system: distal and (asymmetrically) proximal limb muscles; spine (kyphoscoliosis, tethered cord); joints (contractures, hip dysplasia) - Vasculature: spinal cord microvascular endothelium (per the 2024 mouse mechanism data) — UBERON: blood-spinal cord barrier - Urinary system: bladder (dysfunction reported) - Integument: skin (dryness/fissuring in a subset)

Suggested UBERON terms: UBERON:0001017 (central nervous system) — not primary; UBERON:0002240 (spinal cord), UBERON:0002423 (anterior horn), UBERON:0001519 (larynx), UBERON:0002616 (diaphragm), UBERON:0001846 (cochlea), UBERON:0002471 (skeletal muscle organ), UBERON:0007798 (skeletal system), UBERON:0001981 (blood vessel endothelium).

Tissue/cell level: Lower motor neurons (anterior horn cells); axons of peripheral motor nerves; laryngeal muscles; vascular endothelial cells of the spinal cord microvasculature (mechanistically central per 2024 mouse data); cochlear hair cells/stria vascularis (candidate site for hearing loss, given TRPV4's proposed role transporting K⁺ into the endolymph at the DFNA25 locus).

Subcellular: Plasma membrane (TRPV4 channel localization); cytoskeleton (RhoA-regulated actin remodeling); N-/C-terminal intrinsically disordered cytosolic domains (site of regulatory ubiquitination).

Suggested GO Cellular Component terms: GO:0005886 (plasma membrane), GO:0015629 (actin cytoskeleton).

Laterality: Weakness/wasting and vocal-fold paresis are frequently asymmetric — a distinguishing clinical clue versus typical symmetric length-dependent CMT (GeneReviews NBK201366; left side often more severely affected for vocal fold paresis).

8. Temporal Development

Onset: Extremely variable — "usually between early childhood and age 25 years," documented range birth to 8th decade+ (GeneReviews NBK201366). Onset pattern is generally insidious/chronic rather than acute, though congenital presentations (overlapping CDSMA) exist at the severe end of the spectrum.

Progression: Chronic, generally slowly progressive; disease course pattern is progressive rather than relapsing-remitting. Severity is markedly variable even within a family sharing the identical variant, consistent with variable expressivity. No formalized clinical staging system specific to CMT2C exists (unlike, e.g., cancer staging); severity is generally described qualitatively (mild/moderate/severe) and via CMT-specific functional scales (e.g., CMTNS) in the broader CMT literature.

Duration/course: Chronic, lifelong. Most patients have a normal lifespan; the most severely affected (especially those with significant respiratory/diaphragmatic involvement) may have reduced life expectancy from respiratory complications (GeneReviews NBK201366).

Remission: Not a relapsing-remitting disease; no spontaneous remission pattern is described. Pregnancy-associated worsening typically resolves postpartum (see §2).

Critical periods: Early recognition of laryngeal/respiratory involvement is clinically critical because airway compromise (from vocal-fold paresis plus superimposed URI-related edema) can be acutely life-threatening, making this a key intervention window distinct from the general limb-weakness natural history.

9. Inheritance and Population

Epidemiology: CMT2C is rare among an already-rare disease group. TRPV4 pathogenic variants account for ~1–3.5% of CMT2/hereditary motor neuropathy (HMN) overall (GeneReviews NBK201366). In specific published cohorts: - 13/422 individuals (<1%) with a general CMT2 phenotype carried heterozygous TRPV4 variants; this rose to 9–16% among CMT2 patients selected for additional atypical features (vocal fold weakness, diaphragmatic paresis, skeletal dysplasia) (GeneReviews NBK201366; Neurology 2015, WNL.0000000000000450) - A USA cohort of 62 unrelated CMT2 patients (MFN2/GARS/NEFL/GDAP1-negative) found 2 TRPV4 mutations (R316C, R269C) — ~3.2% (NeuroMolecular Medicine 2019) - Incidence across European/Australian axonal-neuropathy cohorts ranges 0–7%, and data from outside Europe/Australia/USA remain largely unknown (Neurology 2015) - Orphanet epidemiologic class: rare disease (prevalence class consistent with "<1/1,000,000" to "not yet documented" tier typical of CMT2 subtypes; exact Orphanet prevalence class was not directly captured in this search — recommend confirming via a direct Orphanet epidemiology table pull before finalizing).

Inheritance: Autosomal dominant, by definition (OMIM 606071). Recurrence risk to offspring of an affected individual is 50%.

Penetrance: Reduced — not all variant carriers manifest symptoms, and asymptomatic/subclinically affected carriers are documented (GeneReviews NBK201366; MedGen 342947).

Expressivity: Highly variable — same variant can produce anything from a CMT2C-limb phenotype to SPSMA to CDSMA to a mixed neuropathy/skeletal-dysplasia phenotype, even within one family (review PMC10311707).

Genetic anticipation: Not reported as a feature (this is a channelopathy caused by point missense variants, not a repeat-expansion disorder).

Germline mosaicism: Not specifically documented in the literature reviewed here (data gap).

Founder effects: Not established for CMT2C specifically; the recurrent Arg-residue "hotspot" variants (e.g., R269C/H, R316C/H) likely reflect mutational hotspots at CpG-type or structurally constrained codons rather than a single founder haplotype, though this was not explicitly confirmed in the sources reviewed.

Consanguinity: Autosomal dominant CMT2C does not require consanguinity; however, homozygous TRPV4 mutations have been reported causing the more severe, biallelic congenital distal SMA/arthrogryposis phenotype in a consanguineous setting (Neurology Genetics, NXG.0000000000000312) — a distinct, allelic (not identical) disease entity.

Carrier frequency: Not established at a population level (extremely rare, largely private variants).

Population demographics: No specific ethnic or geographic predilection has been established for CMT2C; cases have been reported across European, North American, and Asian cohorts. Sex ratio: no strong skew reported (autosomal dominant disorder).

10. Diagnostics

Molecular genetic testing (primary/definitive): - Sequence analysis of TRPV4 is first-line, detecting missense, nonsense, splice-site variants, and small indels; identifies ~100% of currently known pathogenic variants; whole-gene deletion/duplication has not been reported in the autosomal dominant neuromuscular phenotype (GeneReviews NBK201366) - Testing modalities: single-gene sequencing, multigene CMT/HMN panels (including the differential-diagnosis gene list below), or phenotype-focused exome analysis

Electrophysiology (EMG/NCV): - Reduced compound motor action potential (CMAP) amplitudes with normal conduction velocities (>40–60 m/s) — consistent with an axonal/neuronopathic rather than demyelinating process - Sensory nerve action potentials (SNAPs): normal, decreased, or absent - EMG: predominantly chronic neurogenic changes (GeneReviews NBK201366)

Other clinical tests: - Laryngoscopy for vocal fold paresis - Pulmonary function testing and dynamic breathing chest radiographs for diaphragm assessment - Sleep study (central/obstructive sleep apnea screening) - Audiologic evaluation (sensorineural hearing loss) - Skeletal imaging when skeletal-dysplasia overlap is suspected - Spinal MRI to evaluate for tethered cord in appropriate clinical settings

Diagnostic criteria: Diagnosis is established by combining "characteristic clinical and neurophysiologic findings" with identification of a heterozygous TRPV4 variant suspected to cause channel gain-of-function (GeneReviews NBK201366).

Differential diagnosis (genes to exclude/consider): ATP7A, BICD2, BSCL2, DCTN1, DYNC1H1, GARS1, HSPB1, HSPB3, HSPB8, IGHMBP2, JAG1, MYH14, PLEKHG5, SETX, SLC5A7, SMN1 (GeneReviews NBK201366) — these overlap clinically as other distal hereditary motor neuropathies/CMT2/SMA-spectrum disorders.

Screening: No population-based newborn screening; genetic counseling and predictive/cascade testing are offered to at-risk relatives given autosomal dominant inheritance and 50% recurrence risk, with the caveat that penetrance/expressivity cannot be predicted.

11. Outcome/Prognosis

• Survival: Most affected individuals have a normal lifespan. A subset with severe respiratory (diaphragmatic) involvement may have shortened life expectancy secondary to respiratory complications (GeneReviews NBK201366).
• Morbidity: Chronic motor disability (distal and proximal weakness, foot deformity, need for orthoses/mobility aids), laryngeal dysfunction with aspiration/airway risk, restrictive respiratory impairment, progressive hearing loss, and skeletal complications (scoliosis, contractures, hip dysplasia, tethered cord in ~7.5% of one 40-patient cohort).
• Complications: Airway obstruction precipitated by intercurrent URI in the context of pre-existing vocal fold paresis is a specifically flagged acute risk. Aspiration pneumonia risk from laryngeal dysfunction. Sleep-disordered breathing (including central sleep apnea).
• Recovery potential: The underlying motor neuron/axonal loss is not reversible with current standard-of-care (supportive) management; functional improvement is achieved via orthotic/surgical/rehabilitative support rather than disease reversal. The investigational TRPV4-inhibitor pipeline (see §12) specifically aims to change this by targeting the causal channel gain-of-function.
• Prognostic factors: Variant identity/position (correlating with degree of baseline Ca²⁺ elevation) predicts development of mixed neuropathy-skeletal phenotypes and in vitro sensitivity to pharmacologic channel inhibition — a mechanistic biomarker relevant to future trial stratification (PMC8935273).

12. Treatment

There is currently no approved disease-modifying therapy; management is supportive/multidisciplinary, though a mechanistically targeted therapeutic is in active clinical development.

Multidisciplinary supportive care (NCIT terms suggested in parentheses): - Orthotic/mobility support: supportive shoes, orthotics, ankle-foot orthoses/knee-ankle-foot orthoses; orthopedic surgery for severe foot deformity (NCIT:C16186, Orthopedic Surgical Procedure); mobility aids and exercise as tolerated (NCIT:C15302, Physical Therapy) - Laryngeal management: vocal fold lateralization surgery or tracheostomy in severe airway compromise; speech therapy (NCIT:C15329, Surgical Procedure; speech-language therapy term) - Respiratory management: noninvasive ventilatory support, pulmonary function monitoring (NCIT:C15747, Supportive Care) - Spinal/orthopedic management: kyphoscoliosis management; neurosurgical release of tethered spinal cord when symptomatic - Audiology: hearing aids/rehabilitation - Genetic counseling (NCIT:C15240) - Preventive care: avoidance of obesity, avoidance of known neurotoxic medications, prompt treatment of URIs

Experimental/targeted therapeutics (therapeutic_modality: SMALL_MOLECULE, mechanism: TRPV4 channel antagonism): - ABS-0871 (Actio Biosciences) — a novel oral TRPV4 inhibitor purpose-built for TRPV4-positive CMT2C. First-in-human Phase 1 healthy-volunteer trial dosing began March 2025; the drug received FDA Orphan Drug Designation and Rare Pediatric Disease Designation in August 2024. In "novel construct-valid preclinical CMT2C rare disease models," ABS-0871 produced "marked improvements in motor function and mobility compared to untreated controls" (BioSpace press release; CMTAUSA; Actio Biosciences). - Proof-of-concept preclinical rescue: Trpv4 knock-in mice with the severe, rapidly fatal neuromuscular phenotype can be rescued by pharmacologic inhibition of TRPV4 channel activity (GeneReviews NBK201366), providing strong mechanistic rationale for the antagonist approach. - Other TRPV4 antagonist tool/clinical compounds (used in broader TRPV4-pathy research, not CMT2C-specific trials): HC-067047 (a pyrrolocarboxamide research antagonist, IC50 ~48 nM human TRPV4) and GSK2798745 (a spiro-carbamate that advanced to Phase II for heart failure/pulmonary edema indications, demonstrating human tolerability of TRPV4 antagonism as a drug class) (MedChemExpress HC-067047; PMID 34531959). - CMT Research Foundation / HNF natural history study of TRPV4 neuromuscular disease (CMT2C) is ongoing to characterize disease trajectory and support trial readiness (CMTAUSA natural history; HNF TRPV4 program).

Pharmacogenomics: Not applicable/established for this monogenic channelopathy (no drug-metabolism pharmacogenomic modifier reported).

Treatment strategy: Because the causal lesion is a well-characterized channel gain-of-function, the field's guiding treatment algorithm is genotype-directed small-molecule channel antagonism layered on top of standard multidisciplinary supportive/rehabilitative care — a precision-medicine approach analogous to other channelopathies.

13. Prevention

• Primary prevention: Not applicable in the population sense (autosomal dominant single-gene disorder); the relevant "prevention" lever is reproductive/genetic counseling rather than public-health risk-factor modification.
• Secondary prevention (early detection):
• Genetic counseling and predictive testing for at-risk relatives of a known proband (50% recurrence risk), with explicit counseling that reduced penetrance/variable expressivity precludes reliable phenotype prediction
• Prenatal/preimplantation genetic testing options can be discussed for known familial variants (general reproductive-genetics principle; not specifically documented as routinely used for CMT2C in the sources reviewed)
• Vigilant surveillance for laryngeal/respiratory involvement in known carriers, given the acute-risk nature of airway compromise
• Tertiary prevention (complication avoidance in affected individuals): Recommended annual surveillance per GeneReviews includes neurologic exam/PT assessment, otolaryngology evaluation of laryngeal function, dynamic breathing chest radiograph + pulmonary function tests, sleep study, hearing assessment, musculoskeletal evaluation (contractures, hip dysplasia, scoliosis, tethered cord signs), and weight/height/obesity assessment (GeneReviews NBK201366).
• Agents/circumstances to avoid: Obesity, known neurotoxic medications (per CMT Association neurotoxic drug list), and untreated upper respiratory infections (risk of acute airway compromise from vocal-fold edema).
• Immunization: No CMT2C-specific vaccine strategy; general recommendation would be routine respiratory-pathogen immunization (e.g., influenza) given baseline respiratory vulnerability, though this is inferred rather than explicitly documented in the sources found.
• Genetic counseling: Central to prevention/family planning in this dominant disorder; standard NSGC/ACMG genetic-counseling frameworks apply.

14. Other Species / Natural Disease

• Taxonomy of study organisms: Mus musculus (NCBITaxon:10090), Drosophila melanogaster (NCBITaxon:7227); orthologous Trpv4 gene exists broadly across vertebrates.
• Naturally occurring disease in other species: No naturally occurring companion-animal or wildlife TRPV4 neuropathy analog was identified in this search (this appears to be a human-specific documented clinical entity to date; OMIA search was not directly performed but no hits surfaced organically — flag as a gap to confirm via a direct OMIA query if veterinary relevance is needed).
• Orthologous gene: Mouse Trpv4 (MGI ortholog of human TRPV4) is the basis of the knock-in disease models described below; NCBI Gene entries exist for mouse and other model organisms' Trpv4 orthologs.
• Comparative pathology/evolutionary conservation: The ankyrin-repeat arginine residues mutated in human disease are evolutionarily conserved, which is why mouse knock-in of the orthologous R269C/R232C substitutions faithfully reproduces a severe motor phenotype (see below) — supporting deep functional conservation of the TRPV4 channel-gating mechanism across mammals.
• Zoonotic potential/transmission: Not applicable — this is a non-infectious monogenic channelopathy.

15. Model Organisms

Mouse (mammalian genetic knock-in models): - Trpv4^R269C and Trpv4^R232C knock-in mice (endogenous locus, disease-causing missense knock-ins) exhibit weakness, early lethality, and regional motor neuron loss, closely recapitulating the severe end of the human phenotype spectrum (Chen et al. 2024, PMC11316273; PMID 38776392). - Symptomatic mutant mice show focal disruption of blood–spinal cord barrier (BSCB) integrity, linked to endothelial-cell-autonomous TRPV4 gain-of-function. - Key causal/rescue experiment: Conditional genetic deletion of the mutant Trpv4 allele specifically from vascular endothelial cells (but not from neurons, glia, or muscle) rescues the motor and survival phenotypes — establishing endothelial cells, not neurons, as the primary disease-driving cell type in this model (PMC11316273). - Separately, GeneReviews notes that Trpv4 knock-in mice with a "severe, rapidly progressive fatal neuromuscular phenotype" can be rescued by pharmacologic TRPV4 channel inhibition, directly supporting the small-molecule antagonist therapeutic strategy now in human trials (GeneReviews NBK201366). - Limitations: As with many gain-of-function knock-in models, the mouse phenotype (early lethality, prominent vascular/BSCB pathology) is more acute/severe than the typical chronic, slowly progressive human CMT2C course — the vascular-barrier mechanism's relative contribution in human disease (versus a purely cell-autonomous neuronal mechanism) remains an area of active investigation, representing a human-model translational-fidelity open question worth flagging as a HUMAN_MODEL_MISMATCH-type knowledge gap for KB curation (rodent lethality/BSCB phenotype vs. the typically non-lethal, chronic human trajectory).

Cellular/heterologous models: - HEK293 cells transiently transfected with mutant TRPV4 constructs (the original functional-validation system) — demonstrate increased constitutive/evoked Ca²⁺ channel currents and cytotoxicity for CMT2C-associated variants (Deng et al. 2010; Landouré et al. 2010; PMID 21288981). - Structural biology: Cryo-EM of purified TRPV4–RhoA complexes used to map the disease-residue interface and mechanistically explain gain-of-function (PMC10290081).

Invertebrate models: - Drosophila melanogaster models expressing neuropathy-causing TRPV4 mutants have been used to study the ubiquitination-dependent regulatory mechanism, showing reduced channel ubiquitination and channel overactivity that can be experimentally suppressed by enhancing ubiquitination (Aisenberg et al., PMC9010760; grant description at Grantome F31-NS105404).

Applications: These models collectively support (1) confirmation of the gain-of-function pathomechanism, (2) identification of endothelial cells as an unexpected primary disease-driving cell type, (3) a druggable regulatory node (ubiquitination of channel IDRs), and (4) preclinical proof-of-concept for pharmacologic TRPV4 antagonism as a rational, mechanism-based therapeutic strategy now advancing into human Phase 1 trials (ABS-0871).

Summary of Key Evidence Gaps for Curation

1. No formal prevalence/incidence rate-per-100,000 figure was located specifically for CMT2C (only relative frequency within CMT2 cohorts, 1–3.5% to ~16% in enriched subgroups) — recommend using Orphanet's own epidemiology table (ORPHA:99937) directly if a numeric prevalence class is required.
2. No germline mosaicism or founder-effect data specific to TRPV4 CMT2C were found.
3. No large-scale human transcriptomic/proteomic dataset from patient-derived tissue was identified (model-organism/cell-line data dominate the molecular-profiling literature).
4. No veterinary/naturally-occurring animal disease analog was found (distinguishing this from many other monogenic channelopathies with OMIA entries).
5. The apparent tension between the acute/lethal, endothelial-driven mouse knock-in phenotype and the typically chronic, non-lethal human course is a candidate HUMAN_MODEL_MISMATCH worth explicit curation.

Sources

• OMIM #606071 — Hereditary Motor and Sensory Neuropathy, Type IIC
• OMIM *605427 — TRPV4
• Orphanet 99937 — Autosomal dominant CMT type 2C
• MedGen C1853710
• GARD — CMT2C
• GeneReviews — Autosomal Dominant TRPV4-Related Disorders (NBK201366)
• Deng et al., Nat Genet 2010 — SPSMA and CMT2C are allelic disorders caused by TRPV4
• Landouré et al., Nat Genet 2010 — Mutations in TRPV4 cause CMT2C
• Journal of Human Genetics 2010 — TRPV4-pathy, a novel channelopathy
• Neurology 2011 — TRPV4 mutations and cytotoxic hypercalcemia (PMID 21288981)
• Neurology 2015 — Phenotypic spectrum and incidence of TRPV4 mutations (WNL.0000000000000450)
• NeuroMolecular Medicine 2019 — Incidence/features of TRPV4-linked axonal neuropathies in a USA CMT2 cohort
• BMC Neurology / PMC10311707 — TRPV4 mutation causing CMT2C/SPSMA overlap in one family
• PMC8935273 — TRPV4 mutations causing mixed neuropathy/skeletal phenotypes result in severe gain of function
• PMC10290081 — TRPV4–Rho GTPase complex structures reveal mechanisms of gating and disease
• PMID 33664271 — Neuropathy-causing TRPV4 mutations disrupt TRPV4–RhoA interactions and impair neurite extension
• PMC9010760 — Multiubiquitination of TRPV4 reduces channel activity independent of surface localization
• Grantome F31-NS105404 — Aisenberg, ubiquitination and TRPV4 gain-of-channel function
• PMC11316273 / PMID 38776392 — Gain-of-function TRPV4 in endothelial cells drives blood-CNS barrier breakdown and motor neuron degeneration in mice
• Neurology Genetics NXG.0000000000000312 — Homozygous TRPV4 mutation causes congenital distal SMA and arthrogryposis
• BioSpace — Actio Biosciences ABS-0871 Phase 1 trial announcement
• Actio Biosciences press release
• CMTAUSA — Actio Phase I announcement
• CMTAUSA — Natural History of TRPV4 Neuromuscular Disease (CMT2C)
• HNF-Cure — TRPV4 research program
• PMID 34531959 — Major circulating human metabolite of TRPV4 antagonist GSK2798745
• MedChemExpress — HC-067047
• ClinicalGenome / ClinGen CMT Gene Curation Expert Panel
• ClinVar RCV000645535 (p.Arg774Cys, CMT2C)

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Quotes that could not be checked

There was no text to compare these against, so they are neither confirmed nor contradicted:

• DOI:10.1212/WNL.0b013e31820f2de3: "cytotoxic hypercalcemia"
• Reference resolved but exposes no abstract or full text to search

All extracted references resolved successfully.