Genetics of Hereditary Neuropathies
Hereditary motor and sensory neuropathies (HMSN) have been previously classified on the basis of clinical course, mode of inheritance and neuropathological findings . In the past years, considerable advances in the knowledge of this heterogeneous group of disorders have been made due to genetic studies demonstrating that duplication, deletion or mutation of specific genes of the peripheral myelin are the most common causes of HMSN. The classification of HMSN and of related disorders, from now forward called with the eponymous Charcot-Marie-Tooth disease (CMT), is continuously evolving. CMT has a prevalence of 1 case every 2500  and is divided into CMT1 and CMT2 according to neurophysio-logic and neuropathologic findings. In fact, in CMT1 the motor nerve conduction velocity (MNCV) of the median nerve is < 38 m/s. Nerve biopsy shows hypertrophy of the nerve, demyelination and remyelination of the nerve fibers, and Schwann cell proliferation around the demyelinated fibers in an “onion bulb” fashion. In contrast, in CMT2 MNCV is only slightly lowered (> 38 m/s) and sural nerve biopsy shows signs of primary axonal involvement with minimal signs of myelin sufferance. CMT1 and CMT2 are usually inherited as dominant disorders and are clinically indistinguishable. A severe form of CMT called Dejerine-Sottas syndrome (DSS) has onset in early childhood and a progressive and disabling clinical course.
KeywordsMyelin Sheath Myelin Protein Onion Bulb Motor Nerve Conduction Velocity Sural Nerve Biopsy
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