Autosomal recessive distal muscular dystrophy: normal expression of dystrophin, utrophin and dystrophin-associated proteins in muscle fibers.

We examined 19 muscle biopsies from 14 patients with autosomal recessive distal muscular dystrophy (DisMD) histochemically and immunohistochemically to characterize the histologic features of this disease and to determine whether dystrophin and dystrophin-associated proteins (DAPs) are normally present in the muscles of patients with this disorder. The common histologic features in DisMD were active muscle fiber necrosis and regeneration with variation in fiber size, predominantly in the gastrocnemius muscle. There were occasional disorganizations of the intermyofibrillar network such as moth-eaten appearance, lobulated, whorled and targetoid fibers. In one half of the patients, small angular fibers and scattered rimmed vacuoles were also found. On immunohistochemical examination, dystrophin, DAPs, spectrin and laminin were normally expressed along the surface membrane of muscle fibers, even in the advanced stages of the disease. In contrast, dystrophin was absent and DAPs reduced in the sarcolemma of Duchenne muscular dystrophy (DMD) muscles. The overall histochemical features in DisMD were similar to those seen in DMD, though dystrophin and DAPs were normally expressed even in severely affected gastrocnemius muscle. A defect in an as yet unidentified protein rather than in DAPs and dystrophin is probably responsible for the muscle fiber necrosis in DisMD.