MILD CLINICAL PHENOTYPE IN A 12-YEAR-OLD BOY WITH PARTIAL MEROSIN DEFICIENCY AND CENTRAL AND PERIPHERAL NERVOUS-SYSTEM ABNORMALITIES

We found partial merosin deficiency in a boy presenting at 12 yr with marked limb weakness and a waddling gait. Magnetic resonance imaging ( MRI) showed the characteristic white matter abnormalities of merosin-n egative congenital muscular dystrophy. There were also peripheral demy elinating polyneuropathy and evoked potential abnormalities. Unlike cl assic merosin-negative congenital muscular dystrophy, however, our pat ient was less hypotonic and weak and was able to achieve independent w alking. Both by immunohistochemistry and Western blot merosin was show n to be moderately reduced. By immunostaining the alpha 1 laminin chai n was overexpressed and the beta 1 laminin chain was reduced. A spectr um of clinical phenotypes is likely to become evident in merosin-defic ient patients in relation to the discovery of a range of molecular def ects in, and variable expression of, this protein.