CMT

CMT
Name	CMT
Synonyms	Charcot–Marie–Tooth disease; hereditary motor and sensory neuropathy; peroneal muscular atrophy
Specialty	Neurology; Medical genetics; Rehabilitation medicine
Symptoms	Muscle weakness; Foot deformities; Sensory loss; Gait disturbance
Complications	Foot ulcers; Respiratory involvement; Scoliosis; Hearing loss
Onset	Childhood to adulthood
Duration	Lifelong
Causes	Genetic mutations
Diagnosis	Clinical examination; Electrophysiology; Genetic testing
Treatment	Supportive care; Orthoses; Physiotherapy; Surgery; Gene-specific therapies (experimental)
Frequency	1 in 2,500 to 1 in 12,500 (varies by subtype)

CMT

Charcot–Marie–Tooth disease is a group of hereditary peripheral neuropathies characterized by progressive distal motor and sensory impairment. First described in the late 19th and early 20th centuries, this disorder encompasses multiple genetically distinct forms that affect peripheral nerves and neuromuscular function. Management emphasizes multidisciplinary supportive care, with emerging molecular therapies under investigation by academic centers and industry consortia.

Definition and Overview

Charcot–Marie–Tooth is an umbrella term for hereditary neuropathies that predominantly involve peripheral nerve degeneration leading to distal weakness and sensory loss. Classic descriptions link historical clinicians Jean-Martin Charcot, Pierre Marie, and Howard Henry Tooth, with later genetic delineation by groups at institutions such as NIH, Johns Hopkins Hospital, and Mayo Clinic. Major clinical and research frameworks have been established by organizations including the European Neuromuscular Centre, Muscular Dystrophy Association, and patient groups like CureCMD and Muscular Dystrophy UK.

Types and Classification

Subtypes are classified by inheritance pattern, nerve pathology, and genetic etiology. Major categories include demyelinating forms (historically type 1), axonal forms (type 2), intermediate forms, and X-linked variants. Commonly reported genetic causes include duplications of the PMP22 gene, mutations in MPZ, GJB1 (encoding connexin32), and mutations in MFN2. Large-scale genotype–phenotype mapping has been advanced by consortia such as the International CMT Consortium, and classification systems reference standards from OMIM and the World Health Organization nomenclature committees.

Genetics and Pathophysiology

Pathogenic mechanisms vary by gene. PMP22 duplication produces abnormal myelin and demyelination via dosage-sensitive dysregulation; point mutations in MPZ disrupt myelin protein zero structure; GJB1 mutations impair gap junctions in Schwann cells; MFN2 mutations alter mitochondrial fusion affecting axonal transport. Cellular pathways implicated include Schwann cell myelination, axonal transport, mitochondrial dynamics, and ubiquitin–proteasome handling. Model systems developed at laboratories in Harvard University, Stanford University, University College London, and University of Oxford use transgenic mice and induced pluripotent stem cells to study electrophysiological correlates and remyelination strategies. Genetic testing strategies leverage panels, whole-exome sequencing, and copy-number assays implemented in clinical labs such as GeneDx and Ambry Genetics.

Clinical Presentation and Diagnosis

Symptoms typically begin with distal weakness, pes cavus, hammertoes, and loss of vibration and proprioception leading to steppage gait and falls. Age at onset ranges from infancy to late adulthood depending on subtype; severe infantile forms and adult-onset variants are recognized. Diagnostic evaluation integrates neurological examination, nerve conduction studies performed in electrodiagnostic units at centers like Mayo Clinic and Cleveland Clinic, and genetic testing guided by algorithms from specialty centers and professional societies such as the American Academy of Neurology and the European Academy of Neurology. Ancillary assessments may include muscle MRI used in research at Karolinska Institutet and auditory testing for syndromic associations described by groups at Johns Hopkins.

Management and Treatment

There is no universal cure; treatment focuses on symptomatic and rehabilitative strategies. Multidisciplinary care teams including neurologists, physiatrists, orthopedic surgeons, podiatrists, and genetic counselors coordinate interventions. Orthoses and custom footwear designed by clinics at Shriners Hospitals for Children reduce deformity and falls; tendon transfer and corrective osteotomy are surgical options described in literature from Hospital for Special Surgery and Great Ormond Street Hospital. Physical therapy protocols developed at University of Washington and assistive technologies including ankle–foot orthoses and mobility aids improve function. Disease-modifying research includes antisense oligonucleotides, gene-replacement, and small-molecule trials conducted by biotechnology firms and academic centers such as Baylor College of Medicine, University of California San Diego, and collaborations with agencies like FDA for trial design.

Prognosis and Epidemiology

Prognosis varies by genotype and severity; many individuals maintain ambulation into adulthood, while others experience progressive disability. Complications include recurrent falls, chronic pain, and in selected forms respiratory insufficiency or cardiomyopathy, which require surveillance protocols advocated by specialty guidelines from European Neuromuscular Centre and national health systems like the NHS. Prevalence estimates range from about 1 in 2,500 to 1 in 12,500 depending on population genetics, with founder effects documented in populations studied by teams at University of Toronto, University of Copenhagen, and Tel Aviv University. Ongoing registries and natural history studies coordinated through networks such as the Rare Diseases Clinical Research Network inform genotype-specific outcome measures and therapeutic development.

Category:Hereditary neuropathies