Basement membrane abnormality in merosin-negative congenital muscular dystrophy.

In muscle biopsy specimens from three patients with merosin-negative congenital muscular dystrophy (CMD), there was marked variation in fiber size with evidence of necrotic and regenerating processes and with marked interstitial fibrosis. No muscle fibers or intramuscular nerves stained with merosin antibody. On electron microscopy, the basement membrane of all the muscle fibers was very poorly discernible and there were occasional disruptions, while the basement membrane of the Schwann cells was well preserved. On the other hand, the sarcolemmal basement membrane in merosin-positive CMD was well preserved even in patient with severe interstitial fibrosis. It remains to be determined how the defective basement membrane in merosin-negative CMD induces defective sarcolemma and eventual fiber necrosis.