Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth Disease

Introduction

Charcot Marie Tooth Disease is a progressive neurodegenerative disorder characterized by the gradual loss of neuronal function. This page provides comprehensive information about the disease, including its pathophysiology, clinical presentation, diagnosis, and current therapeutic approaches.

Overview

Charcot-Marie-Tooth Disease (CMT), also known as hereditary motor and sensory neuropathy (HMSN), is the most common inherited peripheral neuropathy, affecting approximately 1 in [@spectrum]
2,500 people worldwide[@nerve]. This progressive disorder damages the peripheral nerves, leading to muscle weakness and atrophy, sensory loss, and [@modified]
characteristic foot deformities[@spectrum]. The disease was independently described by three physicians in 1886 - Jean-Martin [@longitudinal]
Charcot and Pierre Marie in France, and Howard Henry Tooth in England - making it one of the oldest known neurological disorders[@modified]. [@openlabel]

Charcot-Marie-Tooth Disease

Introduction

Charcot Marie Tooth Disease is a progressive neurodegenerative disorder characterized by the gradual loss of neuronal function. This page provides comprehensive information about the disease, including its pathophysiology, clinical presentation, diagnosis, and current therapeutic approaches.

Overview

Charcot-Marie-Tooth Disease (CMT), also known as hereditary motor and sensory neuropathy (HMSN), is the most common inherited peripheral neuropathy, affecting approximately 1 in [@spectrum]
2,500 people worldwide[@nerve]. This progressive disorder damages the peripheral nerves, leading to muscle weakness and atrophy, sensory loss, and [@modified]
characteristic foot deformities[@spectrum]. The disease was independently described by three physicians in 1886 - Jean-Martin [@longitudinal]
Charcot and Pierre Marie in France, and Howard Henry Tooth in England - making it one of the oldest known neurological disorders[@modified]. [@openlabel]

CMT represents a heterogeneous group of disorders with over 100 identified genetic causes[@longitudinal]. Despite its prevalence, CMT is often underdiagnosed or misdiagnosed as other neurological [^6]
conditions. The disease typically manifests in adolescence or early adulthood, though onset can occur at any age from childhood to middle age[@openlabel]. While CMT is not considered a [^7]
neurodegenerative disease in the classical sense (it primarily affects the peripheral nervous system rather than the central nervous system), it shares features with other [^8]
neurodegenerative disorders including [axonal degeneration](/mechanisms/sarm1-programmed-axon-degeneration), demyelination, and progressive functional decline[^6]. [^9]

Classification

CMT encompasses over 100 genetic subtypes, classified based on three criteria: (1) the primary nerve structure affected (myelin sheath vs. axon), (2) the inheritance pattern ([autosomal dominant](/mechanisms/genetics), autosomal recessive, or X-linked), and (3) the motor nerve conduction velocity (NCV). The broad classification scheme divides CMT into major categories ([NINDS, 2024](https://www.ninds.nih.gov/health-information/disorders/charcot-marie-tooth-disease)): [^10]

| Type | Primary Pathology | Inheritance | Motor NCV | Prevalence | [^11]
|------|------------------|-------------|-----------|------------| [^12]
| CMT1 | Demyelinating | Autosomal dominant | <38 m/s | ~60% of CMT | [^13]
| CMT2 | Axonal | Autosomal dominant | >38 m/s | ~20% of CMT | [^14]
| CMT4 | Demyelinating | Autosomal recessive | <38 m/s | Rare; more common in consanguineous populations | [^15]
| CMTX | Mixed demyelinating/axonal | X-linked | 25–45 m/s (males) | ~10–15% of CMT | [^16]
| DI-CMT | Intermediate | Autosomal dominant | 25–45 m/s | Rare | [^17]

The "intermediate" forms (DI-CMT) show features of both demyelination and [axonal degeneration](/mechanisms/sarm1-programmed-axon-degeneration), with motor NCV values between the classic demyelinating (<38 m/s) and axonal (>38 m/s) thresholds. [^18]

CMT1 (Demyelinating Type)

• Primary abnormality in the myelin sheath[^7]
• Severely reduced nerve conduction velocities (NCV <38 m/s)[^8]
• "Onion bulb" formations on nerve biopsy[^9]
• Subtypes: CMT1A (PMP22 duplication), CMT1B (MPZ), CMT1C (LITAF), CMT1D (GDAP1)[^10]

CMT2 (Axonal Type)

• Primary abnormality in the nerve axon[^11]
• Normal or near-normal NCV with reduced action potential amplitudes[^12]
• Loss of large myelinated fibers[^13]
• Subtypes: CMT2A (MFN2), CMT2B (RAB7), CMT2C (TRPV4), CMT2D (GARS)[^14]

CMT4 (Autosomal Recessive Demyelinating)

CMT4 represents a group of autosomal recessive demyelinating neuropathies that are typically more severe than [autosomal dominant](/mechanisms/genetics) forms and present earlier in childhood: [^19]

• Age of onset: Usually in the first decade of life; many children present with delayed motor milestones or difficulty walking
• Severity: Often more disabling than CMT1, with earlier wheelchair dependence in some subtypes
• Geographic distribution: More prevalent in populations with higher rates of consanguinity (Mediterranean, Middle Eastern, North African populations) due to recessive inheritance
• Major genetic subtypes:
• CMT4A (GDAP1): Ganglioside-induced differentiation-associated protein 1 mutations; both demyelinating and axonal forms; associated with vocal cord paresis
• CMT4B1/B2 (MTMR2/MTMR13): Myotubularin-related proteins; distinctive "focally folded" myelin sheaths on nerve biopsy
• CMT4C (SH3TC2): SH3 domain and tetratricopeptide repeats 2; most common CMT4 subtype; scoliosis is a prominent feature
• CMT4F (PRX): Periaxin; severe sensory loss with sensory ataxia
• CMT4J (FIG4): Phosphoinositide phosphatase; rapidly progressive course
• Clinical features: Prominent scoliosis, foot deformities, distal limb weakness, and sensory loss; cranial nerve involvement may occur in some subtypes
• Prognosis: Variable, but generally more progressive than dominant forms; many patients require wheelchair by the second or third decade

CMTX (X-Linked)

CMTX is the second most common form of CMT, accounting for approximately 10–15% of all cases. The most common subtype, CMTX1, is caused by mutations in the GJB1 gene encoding connexin-32: [^20]

• GJB1 (Connexin-32): Over 460 different mutations identified; connexin-32 forms gap junctions in [Schwann cells](/cell-types/schwann-cells) that allow diffusion of small molecules between myelin lamellae. Loss of these junctions disrupts Schwann cell communication and myelin maintenance
• NCV values: Intermediate range (25–45 m/s in males), which can complicate classification. Females typically show higher NCV values than affected males
• Sex-dependent severity: Males are more severely affected due to hemizygosity (single X chromosome), with earlier onset and more rapid progression. Females (heterozygous carriers) show variable manifestations due to random X-inactivation — ranging from asymptomatic to moderately affected
• CNS involvement: Unlike most CMT forms, CMTX1 can cause transient CNS symptoms including stroke-like episodes with white matter lesions on MRI, particularly during metabolic stress (fever, high altitude). These episodes are reversible and thought to result from connexin-32 dysfunction in CNS [oligodendrocytes](/cell-types/oligodendrocytes)
• Other CMTX types: CMTX2–CMTX6 are rare subtypes caused by mutations in AIFM1, GJB3, and other X-linked genes

Genetic Basis

Most Common Forms

CMT1A (Duplication of PMP22) [^21]

• Most common subtype, accounting for ~50% of all CMT cases[^21]
• Duplication of the PMP22 gene on chromosome 17p12[^22]
• Overexpression of peripheral myelin protein 22 leads to abnormal myelin formation[^23]
• Variable expressivity even within families[^24]

• Second most common genetic cause of CMT[^25]
• Mitofusin 2 mutations affect mitochondrial trafficking in axons[^26]
• Associated with early-onset severe phenotype[^27]

• Gap junction beta-1 protein (connexin-32) mutations[^28]
• Affects communication between Schwann cells and axons[^29]
• Unique among CMT types for X-linked inheritance[^30]

Other Genes

• MPZ (Myelin Protein Zero): CMT1B, CMT2I/J[^31]
• LITAF: CMT1C[^32]
• SH3TC2: CMT4A[^33]
• GDAP1: CMT4A, CMT2K[^34]
• GARS: CMT2D[^35]
• HSPB1: CMT2F[^36]

Pathophysiology

Demyelinating Mechanisms (CMT1)

• Abnormal myelin production and maintenance[^38]
• Segmental demyelination and remyelination cycles[^39]
• Formation of onion bulb structures (concentric layers of Schwann cell processes)[^40]
• Secondary [axonal degeneration](/mechanisms/sarm1-programmed-axon-degeneration) from chronic [demyelination](/mechanisms/demyelination)[^41]

Axonal Mechanisms (CMT2)

• Impaired axonal transport due to mitochondrial dysfunction[^43]
• Disruption of cytoskeletal dynamics[^44]
• Loss of neuromuscular junctions[^45]
• Wallerian-like degeneration[^46]

Schwann Cell-Axone Interactions

• Failed axonal support[^48]
• Impaired nerve regeneration[^49]
• Altered neurotrophic factor signaling[^50]

Clinical Presentation

Motor Symptoms

• Distal muscle weakness: Beginning in feet and lower legs, progressing to hands[^51]
• Foot drop: Difficulty lifting the front part of the foot, leading to high-stepping gait[^52]
• Muscle atrophy: Particularly in the calves ("stork leg" appearance)[^53]
• Hand weakness: Difficulty with fine motor tasks (buttoning, writing)[^54]
• Reduced reflexes: Particularly at ankles, later at knees[^55]

Sensory Symptoms

• Reduced sensation: Touch, temperature, vibration sense in extremities[^56]
• Sensory ataxia: Unsteady gait, especially in the dark[^57]
• Paresthesias: Tingling or numbness sensations[^58]

Skeletal Deformities

• High arched feet (pes cavus): Very common[^59]
• Hammertoes: Toe deformities[^60]
• Foot inversions: Flat feet or inward-turning feet[^61]
• Scoliosis: In some cases, particularly CMT4[^62]

Other Features

• Tremor: Postural tremor in some patients[^63]
• Pain: Neuropathic pain in up to 30% of patients[^64]
• Sensory neuropathy: Can lead to painless injuries[^65]

Diagnosis

Clinical Assessment

A systematic clinical evaluation is essential for CMT diagnosis and subtype classification: [^28]

• Detailed neurological examination: Quantitative assessment of distal muscle strength (MRC grading), sensory modalities (vibration, proprioception, pinprick, temperature), deep tendon reflexes (often absent at the ankle early in disease), and gait analysis. The CMT Neuropathy Score (CMTNS) is a validated composite outcome measure combining symptoms, signs, and electrophysiological findings, widely used in clinical trials
• Family history and pedigree analysis: Three-generation pedigree to determine inheritance pattern ([autosomal dominant](/mechanisms/genetics), autosomal recessive, X-linked). De novo mutations occur in approximately 10% of CMT1A cases. A negative family history does not exclude CMT
• Physical examination for characteristic deformities: High-arched feet (pes cavus), hammer toes, inverted champagne bottle-shaped legs (distal muscle wasting with preserved proximal muscles), hand intrinsic muscle wasting (claw hand in advanced disease), scoliosis, and hip dysplasia
• Functional assessment: Gait speed, 6-minute walk test, 9-hole peg test for upper extremity function, and patient-reported outcome measures
• Age of onset and progression rate: These help guide genetic testing strategy — early-onset demyelinating forms suggest CMT1A or CMT4, while adult-onset axonal forms suggest CMT2

Electrophysiological Studies

Nerve conduction studies (NCS) and electromyography (EMG) are critical for CMT classification and narrowing the differential diagnosis: [^29]

Nerve Conduction Studies (NCS) [^30]

• Motor NCV: The most important discriminating parameter. Uniform slowing of motor NCV to <38 m/s in the upper extremity median nerve is characteristic of demyelinating CMT (CMT1), while NCV >38 m/s with reduced compound muscle action potential (CMAP) amplitudes indicates axonal CMT (CMT2). Intermediate values (25–45 m/s) suggest CMTX or DI-CMT
• Uniform vs. non-uniform slowing: CMT1 typically shows uniform slowing across all nerve segments (reflecting diffuse dysmyelination from birth), distinguishing it from acquired demyelinating neuropathies (e.g., [CIDP](/diseases/chronic-inflammatory-demyelinating-polyneuropathy) which show non-uniform or multifocal slowing with conduction block and temporal dispersion
• Sensory nerve action potentials (SNAPs): Reduced or absent in both demyelinating and axonal forms; sensory responses are often more severely affected than motor in CMT2
• F-wave latencies: Prolonged in demyelinating forms

• Chronic neurogenic changes: Increased motor unit potential duration and amplitude, reduced recruitment, and polyphasic motor units in distal muscles
• Fibrillation potentials: May be present in actively denervating muscles, more common in CMT2
• Muscle selection: Distal muscles (extensor digitorum brevis, tibialis anterior) are tested first; proximal muscles are typically normal or mildly affected

Genetic Testing

• Comprehensive panel testing: Tests for all known CMT genes[^71]
• Whole exome sequencing: For atypical cases[^72]
• Targeted testing: For known family mutations[^73]

Nerve Biopsy

With the advent of comprehensive genetic testing panels, sural nerve biopsy is now rarely required for CMT diagnosis. However, it remains valuable in specific diagnostic dilemmas: [^32]

• Indications: Atypical presentations where genetic testing is negative; differentiation from acquired inflammatory neuropathies (CIDP vs. CMT); suspected cases with intermediate electrophysiology
• Characteristic findings in demyelinating CMT (CMT1):
• Onion bulb formations: Concentric layers of [Schwann cell](/cell-types/schwann-cells) cytoplasmic processes surrounding a thinly myelinated or demyelinated axon, resulting from repeated cycles of demyelination and remyelination. Generalized onion bulbs throughout the nerve are highly characteristic of inherited demyelinating neuropathy ([Sabet et al., 2019](https://doi.org/10.1002/mus.30810227))
• Uniformly thin myelin sheaths: Reduced myelin thickness relative to axon diameter across all fibers
• Loss of large myelinated fibers: Preferential loss of large-diameter fibers
• Findings in axonal CMT (CMT2): Axonal degeneration with reduced myelinated fiber density; clusters of regenerating axons; minimal onion bulb formation
• Distinguishing inherited from acquired: Generalized onion bulbs predict inherited neuropathy, while mixed onion bulbs with inflammation predict acquired neuropathy
• Electron microscopy: May reveal specific ultrastructural abnormalities such as focally folded myelin (CMT4B), tomacula (HNPP), or abnormal mitochondria

Treatment and Management

No Cure Currently Available

There is currently no FDA-approved disease-modifying therapy for any form of CMT, though the therapeutic landscape is rapidly evolving ([Stavrou et al., 2025](https://doi.org/10.1080/14737175.2025.2470980)). Management focuses on symptomatic treatment, functional preservation, and prevention of secondary complications: [^33]

Emerging Disease-Modifying Approaches [^34]

• PXT3003 (baclofen + sorbitol + naltrexone): The most clinically advanced candidate, designed to downregulate [PMP22](/genes/pmp22) overexpression in CMT1A. The Phase 3 PREMIER trial (387 patients) showed stabilization of disease but did not meet its primary endpoint of significant improvement over placebo on the ONLS scale
• Gene silencing strategies for CMT1A: Since CMT1A is caused by PMP22 gene duplication, reducing PMP22 expression to normal levels is a rational approach:
• Antisense oligonucleotides (ASOs) targeting PMP22 mRNA
• siRNA and shRNA approaches delivered via AAV vectors
• CRISPR-Cas9 gene editing to remove the duplicated PMP22 copy
• Gene replacement therapy: AAV9-mediated delivery of functional genes for loss-of-function CMT subtypes; a Phase I/IIa trial for CMT2S (IGHMBP2 mutations) uses intrathecal AAV9 injection
• AT-007 (govorestat): An aldose reductase inhibitor in Phase 2/3 trials for CMT caused by sorbitol dehydrogenase (SORD) deficiency, the most common autosomal recessive form of axonal CMT
• VM202 (engensis): Plasmid DNA containing hepatocyte growth factor gene; under investigation for neuroprotection in CMT1A

Physical and Occupational Therapy

• Strengthening exercises: Maintain muscle function[^77]
• Stretching exercises: Prevent contractures[^78]
• Gait training: Improve walking efficiency[^79]
• Hand therapy: Preserve fine motor skills[^80]

Orthopedic Interventions

• Ankle-foot orthoses (AFOs): Most commonly prescribed assistive device[^81]
• Custom footwear: Accommodates foot deformities[^82]
• Surgical correction: For severe deformities or contractures[^83]
• Tendon transfers: Improve foot function[^84]

Medications

Pharmacological management in CMT is currently limited to symptomatic relief, with several important considerations: [^35]

• Neuropathic pain management: [Gabapentin](/therapeutics/gabapentin), pregabalin, and duloxetine are first-line agents for neuropathic pain. Tricyclic antidepressants (amitriptyline, nortriptyline) are second-line options. Opioids are generally avoided due to chronic nature of disease
• Muscle cramps and spasticity: Magnesium supplementation, stretching programs; mexiletine may be considered for refractory cramps. Quinine use is controversial due to cardiac risk
• Fatigue: Common and often underrecognized; modafinil has been used off-label in some centers
• Neurotoxic drug avoidance: Critically important — certain medications can exacerbate CMT neuropathy and must be avoided or used with extreme caution:
• Vincristine: Absolutely contraindicated; can cause severe, potentially fatal neuropathy in CMT patients
• Cisplatin and taxanes: High neurotoxic risk; alternatives should be sought for cancer treatment
• High-dose pyridoxine (vitamin B6): Neurotoxic at doses >200 mg/day
• Nitrofurantoin, metronidazole: May worsen neuropathy
• Statins: Controversial; some evidence of exacerbating CMT symptoms
• The Charcot-Marie-Tooth Association (CMTA) maintains an updated list of medications to avoid
• Vitamin supplementation: Vitamin B12 and folate levels should be monitored and supplemented if deficient, though they do not treat the underlying neuropathy

Experimental Approaches

• Gene therapy: AAV-mediated gene delivery in development[^88]
• Small molecules: Neurotrophic factors, PMP22 reducers[^89]
• Antisense oligonucleotides: Targeting specific mutations[^90]
• Stem cell therapy: Schwann cell replacement approaches[^91]

Epidemiology

• Prevalence: 1 in 2,500 people (most common inherited neuropathy)[^92]
• Incidence: 1-5 per 10,000 live births[^93]
• Distribution: Worldwide, no ethnic predilection for most forms[^94]
• Onset: Typically adolescence to early adulthood[^95]
• Progression: Slow, with disability developing over decades[^96]

Related Conditions

CMT shares features with other peripheral neuropathies and some neurodegenerative conditions: [^36]

• [amyotrophic lateral sclerosis](/diseases/amyotrophic-lateral-sclerosis): Shares motor neuron degeneration features
• [Alzheimer's Disease](/diseases/alzheimers-disease): Similar protein misfolding mechanisms in some forms
• [Parkinson's Disease](/diseases/parkinsons-disease): Mitochondrial dysfunction common to both
• [Huntington's Disease](/diseases/huntingtons): Similar genetic inheritance patterns

See Also

• [Peripheral Neuropathy](/diseases/peripheral-neuropathy): Category of nerve disorders
• [Myelin](/mechanisms/demyelination): Nerve covering affected in CMT1
• [Mitochondrial Dynamics](/mechanisms/mitochondrial-dynamics): Affected in CMT2
• [Axonal Transport](/mechanisms/sarm1-programmed-axon-degeneration): Dysregulated in CMT pathogenesis

Background

The study of Charcot Marie Tooth Disease has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development. [^37]

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions. [^38]

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/) - Biomedical literature
• [Alzheimer's Disease Neuroimaging Initiative](https://adni.loni.usc.edu/) - Research data
• [Allen Brain Atlas](https://brain-map.org/) - Brain gene expression data

Recent Research (2024-2026)

This section highlights recent publications relevant to this disease.

• [Nerve Ultrasound in Pediatric Polyneuropathies: A Systematic Review.](https://pubmed.ncbi.nlm.nih.gov/41145127/) (2026 Apr) - Neuropediatrics
• [Spectrum of dominant Charcot-Marie-Tooth disease due to SLC12A6 variants.](https://pubmed.ncbi.nlm.nih.gov/41500801/) (2026 Mar 13) - Journal of neurology, neurosurgery, and psychiatry
• [Modified Lambrinudi Combined With X-Shaped Plate Internal Fixation for Triple Arthrodesis.](https://pubmed.ncbi.nlm.nih.gov/41817136/) (2026 Mar 12) - Foot & ankle international
• [Longitudinal analysis of lipid changes in the sciatic nerve caused by overexpression of PMP22 in murine models of CMT1A.](https://pubmed.ncbi.nlm.nih.gov/41825735/) (2026 Mar 11) - Journal of lipid research
• [An open-label single-arm phase 1/2a study to evaluate the safety and exploratory efficacy of a VM202 in patients with Charcot-Marie-Tooth disease 1A.](https://pubmed.ncbi.nlm.nih.gov/41787447/) (2026 Mar 5) - Orphanet journal of rare diseases

References