X-LINKED DOMINANT HEREDITARY MOTOR AND SENSORY NEUROPATHY
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Modern techniques have defined the hereditary motor and sensory neuropathies (HMSN) as a genetically heterogeneous group of disorders. This includes a rare variant with X-linked dominant inheritance. We have traced this disorder through 6 generations of a large Canadian kindred; neurological and electrophysiological examinations were performed in 57 family members and nerve biopsies were studied in 2 affected males, early and late in the disease; 42/83 family members were affected. No male-to-male transmission was encountered in 19 sons of affected fathers, whereas all their daughters expressed the disease. Linkage was shown to the DNA loci DXYS1 Z max = 2.87 at theta max = 0.06 and to PGK1 Z max = 1.51 at theta max = 0 (Beckett et al., 1986). The typical clinical features are onset in early childhood, pes cavus, atrophy and weakness of peroneal muscles and intrinsic hand muscles, and sensory abnormalities. Males were severely affected, whereas females had mild or subclinical disease. Electrophysiological observations indicated a substantial loss of distal motor and sensory nerve fibres. Evoked compound muscle action potentials in extensor digitorum brevis were absent or severely reduced in 42% of cases and the peroneal motor nerve conduction velocity was mildly reduced to a mean 36.5 +/- 7.4 m.s-1. Sural sensory nerve action potentials were absent or severely reduced in 75% of those affected. Nerve biopsies showed loss of myelinated and unmyelinated nerve fibres, regenerative sprouting and secondary demyelination. The findings indicate that this distinct variant of HMSN is the result of primary axonal degeneration.
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