DIFFERENTIAL ELECTROPHYSIOLOGICAL FEATURES OF NEUROPATHIES ASSOCIATEDWITH 17P11.2 DELETION AND DUPLICATION

Hereditary neuropathy with liability to pressure palsies (HNPP) and he reditary motor-sensory neuropathy type IA (HMSN IA) are quite distinct clinical entities recently associated to deletion and duplication, re spectively, of the 17p11.2 segment including the gene for peripheral m yelin protein 22 (PMP-22). We stud led the electrophysiological featur es of 48 HNPP and 62 HMSN IA motor nerves. Conduction velocities (CV) and compound muscle action potential amplitudes were significantly red uced and distal latencies prolonged in HMSN IA compared to HNPP. CV wa s uniformly slowed in HMSN IA nerves whereas in HNPP it was focally sl owed in 80% of ulnar and 12% of peroneal nerves at usual compression s ites. Conduction block was present in 6% of HNPP nerves but in none of HMSN IA. In conclusion: (1) HMSN IA with 17p11.2 duplication presents marked, diffuse, and uniform slowing; (2) HNPP with 17p11.2 deletion presents focal electrophysiological abnormalities possibly correlated with the presence of tomaculae; and (3) under- and overexpression of P MP-22 in concurrence with environmental factors might be responsible f or the distinctive features of HNPP and HMSN IA. (C) 1995 John Wiley & Sons, Inc.