Charcot-Marie-Tooth disease and related peripheral neuropathies

Soon after the description of Charcot-Marie-Tooth disease (CMT) in 1886, it became apparent that this syndrome is clinically and genetically heterogeneous. Neuropathological and electrophysiological studies have further dissected this syndrome into distinct categories that are now classified in a complex nosology of the inherited peripheral neuropathies. The recent advent of molecular genetics has dramatically increased our understanding of the underlying disease mechanisms. Genetic linkage studies have identified at least 17 genetic loci for different types of inherited neuropathies although most genes involved still remain to be found. The application of molecular genetics has already had an important impact on clinical practice and genetic counselling. Three genes responsible for hereditary motor and sensory neuropathy type I (HMSNI) or CMT1 have been identified: peripheral myelin protein 22 (PMP22) and myelin protein zero (MPZ) for the autosomal dominant form and connexin 32 (Cx32) for the X-linked dominant variant. The PMP22 gene is also involved in the majority of families with hereditary neuropathy with liability to pressure palsies (HNPP). The observation of a 1.5 Mb tandem duplication in chromosome 17p11.2, containing the PMP22 gene, in CMT1 and the reciprocal deletion in the same region in HNPP has provided a novel disease paradigm for autosomal dominant disorders, i.e. the gene dosage mechanism. The study of phenotype-genotype correlations in transgenic animal models for PMP22, MPZ and Cx32 mutations will help elucidate the underlying disease mechanisms and will provide a basis for gene therapy and/or other therapeutic approaches such as treatment with neurotrophic growth factors.