loss of function in HNPP

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(Note: HNPP or Hereditary Neuropathy with Liability to Pressure Palsies

is the genetic opposite of CMT. It can have some similiar symptoms as

CMT.)

Abstract from Muscle Nerve. 2004 Feb;29(2):205-10.

Loss-of-function phenotype of hereditary neuropathy with liability to

pressure palsies.

Li J, Krajewski K, RA, Shy ME.

Department of Neurology, Wayne State University School of Medicine, 4201

St. Antoine, UHC-8D, Detroit, Michigan 48201, USA.

Hereditary neuropathy with liability to pressure palsies (HNPP) provides

a human model to investigate the role of PMP22 in myelinated peripheral

nerve, since the disease is caused by a deletion of one of the two PMP22

alleles. To systematically characterize the

phenotype of HNPP, we prospectively evaluated the clinical features and

electrophysiological findings in 17 genetically confirmed patients, 7

men and 10 women, ranging in age from 9 to 66 years (mean, 41 +/- 13).

Fifteen symptomatic patients presented with episodes of transient focal

weakness or sensory loss that were usually related to particular

activities causing nerve compression, including stretching or minor

repetitive focal trauma. No patient sought medical attention for

symptoms of a symmetric polyneuropathy. Neurological examinations were

either normal or mildly abnormal. Neither focal slowing of nerve

conduction studies, nor reduction in compound muscle action potential

(CMAP) or sensory nerve action potential (SNAP) amplitudes

consistently predicted the site of symptoms. We conclude that the

majority of patients with HNPP present with transient, recurrent, focal

symptoms of weakness or sensory loss in the distribution of individual

nerves or plexus, and that a diffuse symmetric sensorimotor

polyneuropathy is an unusual presentation of HNPP. These studies

suggest that the function of PMP22, at least in part, is to stabilize

myelin so that it will be protected from injuries resulting from

repetitive, minor trauma.