Molecular genetics of Charcot-Marie-Tooth disease and related neuropathies.

Collectively, the inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B), the X chromosome (CMTX) and to another unknown autosome (CMT1C). CMT1A is most often associated with a tandem 1.5 megabase (Mb) duplication in chromosome 17p11.2-12, or in rare patients may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (P0) gene. The molecular defect in CMT1C is unknown. X-linked Charcot-Marie-Tooth neuropathy (CMTX) is associated with mutations in the connexin32 gene. Charcot-Marie-Tooth neuropathy type II (CMT2) is an axonal neuropathy, also of undetermined cause. One form of CMT2 maps to chromosome 1p36 (CMT2A). Dejerine-Sottas disease, also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene of the P0 gene. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5 Mb deletion in chromosome 17p11.2-12 and may result from reduced expression of the PMP22 gene. CMT1A and HNPP are apparent reciprocal duplication/deletion syndromes originating from unequal crossover during germ cell meiosis.