We screened for SH3TC2 pathogenic variants in 84 AR or sporadic CMT probands, PMP2 pathogenic variants in 39 AD or sporadic CMT1 probands, and BSCL2 pathogenic variants in 50 AD or sporadic CMT2 probands, using polymerase chain reaction and Sanger sequencing.
1] According to electrophysiological features, CMT is divided into CMT1 (median nerve conduction velocity [MNCV] <38 m/s) and CMT2 (MNCV >38 m/s).
Charcot Marie Tooth 1 (HMSN type I according to Dyck's classification), comprises the group of demyelinating peripheral neuropathies and CMT2 (HMSN type II) comprises the axonal peripheral neuropathies (3).
The basis of this recommendation is classifying CMT according to the NCV findings into CMT1, CMT2, or intermediate between CMT1 and CMT2.
Disease Pathology Inheritance Genes/chromosomal name (a) mode loci associated with disease, n CMT1 Abnormal myelin AD (b) 9 CMT2 Axonopathy AD 19 CMT4 Either myelinopathy AR 10 or axonopathy CMTX Axonopathy with XLD 2 secondary myelin changes Disease Proportion name (a) of all CMT, % CMT1 40-50 CMT2 10-15 CMT4 Rare CMTX 10-15 (a) Intermediate dominant (dominant inheritance with NCV between demylinating and axonopathic) and other rare forms are not included.
CMT2 (autosomal dominant) and ARCMT2 (autosomal recessive) refer to an hereditary motor and sensory neuropathy in which nerve conduction velocity is usually within the normal range, although occasionally falling, into the low normal or mildly abnormal range (35-50 m/s), but presenting reduced compound muscle action potential (CMAP) (Dyck et al.
The clinical features of CMT2 patients overlap extensively with CMT1, although, patients with CMT2 tend to be less disabled and have less sensory loss, whereas X-linked form of CMT may present an axonally pronounced form of CMT that could be confused with CMT2 (Young et al.