Inherited neuropathies.
Charcot-Marie-Tooth neuropathy (CMT) type 1 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-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. CMTX is associated with mutations in the connexin 32 gene. CMT2 is an axonal neuropathy of undetermined cause. One form of CMT2 maps to chromosome 1p36 (CMT2A). Dejerine-Sottas disease is a severe, infantile-onset demyelinating polyneuropathy that may be associated with point mutations in either the PMP22 gene or the P0 gene. Hereditary neuropathy with liability to pressure palsies (HNPP) is 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. Most examples of CMT1A and HNPP are reciprocal duplication or deletion syndromes originating from unequal crossover during germ cell meiosis. Familial amyloid polyneuropathy (FAP) is an autosomal dominant disorder that classically presents with a sensory peripheral neuropathy and early autonomic involvement. Transthyretin (TTR) is the most common constituent amyloid fibril protein deposited in FAP, and there are now 28 point mutations in the TTR gene described in TTR-related FAP. Liver transplantation looks promising as a treatment for TTR-related FAP.