From the syndrome of Charcot, Marie and Tooth to disorders of peripheral myelin proteins.

The description of the peroneal muscular atrophy syndrome in 1886 by Charcot, Marie and Tooth was followed by an era of nosological confusion. This was partly clarified by the advent of nerve conduction studies and the definition of the most common, but heterogeneous, disorders underlying this syndrome, hereditary motor and sensory neuropathies (HMSN) types I and II. The classification of HMSN is now changing as a result of the identification of underlying mutations in genes encoding myelin proteins. Abnormalities of peripheral myelin protein 22 (PMP-22) account for dominantly inherited HMSN type I in approximately 90% of families. The commonest genetic defect is a duplication of this gene and the surrounding region of chromosome 17, although point mutations also occur. A deletion of the same region causes hereditary neuropathy with liability to pressure palsies. Point mutations of the P0 gene cause HMSN I in a small number of families. The X-linked type of HMSN is associated with defects of the connexin 32 gene, which encodes a gap junction protein. These molecular genetic advances can be translated into clinical practice, leading to improved diagnosis and genetic counselling.