Charcot-marie-tooth Disease, Demyelinating, Type 1b; Cmt1b

Description

Charcot-Marie-Tooth disease is a sensorineural peripheral polyneuropathy. Affecting approximately 1 in 2,500 individuals, Charcot-Marie-Tooth disease is the most common inherited disorder of the peripheral nervous system (Skre, 1974). Autosomal dominant, autosomal recessive, and X-linked forms have been recognized. ClassificationOn the basis of electrophysiologic properties and histopathology, CMT has been divided into primary peripheral demyelinating (type 1, or HMSNI) and primary peripheral axonal (type 2, or HMSNII) neuropathies. The demyelinating neuropathies classified as CMT type 1 are characterized by severely reduced motor NCVs (less than 38 m/s) and segmental demyelination and remyelination with onion bulb formations on nerve biopsy. The axonal neuropathies classified as CMT type 2 are characterized by normal or mildly reduced NCVs and chronic axonal degeneration and regeneration on nerve biopsy (see CMT2A1; {118210}). Distal hereditary motor neuropathy (dHMN) (see {158590}), or spinal CMT, is characterized by exclusive motor involvement and sparing of sensory nerves (Pareyson, 1999).McAlpine (1989) proposed that the forms of CMT with very slow nerve conduction be given the gene symbol CMT1A (OMIM ) and CMT1B, CMT1A being the gene on chromosome 17 and CMT1B being the gene on chromosome 1. CMT2 was the proposed symbol for the autosomal locus responsible for the moderately slow nerve conduction form of the disease (axonal).For a phenotypic description and discussion of genetic heterogeneity of the various subtypes of CMT, see CMTX1 (OMIM ), CMT2A1 (OMIM ), CMT3 (DSS ), CMT4A (OMIM ), and CMTDIB (OMIM ). Genetic Heterogeneity of Autosomal Dominant Demyelinating CMT1Autosomal dominant demyelinating CMT1 is genetically heterogeneous disorder and can be caused by mutations in different genes (see CMT1A, {118220}; CMT1C, {601098}; CMT1D, {607678}), CMT1E (OMIM ), and CMT1F (OMIM ). See also {608236} for a related phenotype characterized by isolated slowed nerve conduction velocities (NCVs).

Clinical Features

• Hearing impairment
• Ataxia
• Muscle weakness
• Pain
• Peripheral neuropathy
• Skeletal muscle atrophy
• Optic atrophy
• Tremor
• Cardiomyopathy
• Blindness

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