DEMYELINATING PERIPHERAL NEUROPATHY IN MEROSIN-DEFICIENT CONGENITAL MUSCULAR-DYSTROPHY

It has recently been shown that merosin, a laminin variant, is deficie nt in a proportion of patients with congenital. muscular dystrophy. Me rosin is a heterotrimer composed of the alpha 2, beta 1, and gamma 1 s ubunits, and further studies have shown that it is the alpha 2 subunit that is deficient in these patients. Because the alpha 2 subunit is a lso expressed in S-merosin, found in Schwann cells, we have investigat ed whether peripheral nerve function is also affected in these patient s. Motor nerve conduction velocities and sensory distal latencies were examined in 25 cases of congenital muscular dystrophy and the results correlated with the merosin expression in their muscle biopsies. All but two of the 10 merosin-deficient cases had reduced motor nerve cond uction, whereas all the merosin-positive cases had normal results. Ana lysis of the biopsies of these two cases showed that they produced mer osin in reduced amounts, in contrast to all other merosin-deficient pa tients that produced no or only traces of merosin. Sensory nerve studi es showed no difference between the two groups. These results indicate that a peripheral demyelinating neuropathy is a feature of merosin-de ficient congenital muscular dystrophy. The fact that the alpha 2 subun it is also expressed in Schwann cells supports the idea that the alpha 2 gene, located on chromosome 6, is the candidate gene for merosin-de ficient congenital muscular dystrophy.