Hereditary motor-sensory neuropathies. Charcot-Marie-Tooth syndrome

The Charcot-Marie-Tooth (CMT) syndrome is also referred to as hereditary motor-sensory neuropathy (HMSN). It is not a single disease but has a multitude of genetic causes. The typical clinical characteristics are distal muscle weakness and atrophy, depressed tendon reflexes, often slow motor NCV, and the frequent finding of other similarly affected relatives. The most common variant of this syndrome is HMSN-I showing autosomal dominant inheritance, markedly slow motor NCV and nerve hypertrophy. One form of HMSN-I is linked to the Duffy locus on chromosome 1. There are numerous other varieties of HMSN including other autosomal dominant conditions such as HMSN-II (with nearly normal motor NCV) and several types of familial amyloid neuropathy (with specific amino acid substitutions in transthyretin); autosomal recessive conditions such as HMSN-III (Déjérine-Sottas hypertrophic neuropathy of childhood) and Refsum's disease (defect of phytanic acid metabolism); and conditions produced by mutations on the X chromosome such as X-linked HMSN, Fabry trihexoside storage disease, and adrenomyeloneuropathy. The known biochemical abnormalities, chromosomal locations, clinical findings and genetic counseling of these disorders are reviewed.