[MIM*310300] a generally benign type of muscular dystrophy, with onset in childhood or early adulthood. Weakness begins with the pectoral girdle and proximal upper extremity muscles and spreads to the pelvic girdle and distal lower extremity muscles. Contractures of the elbow, flexors, neck flexors, and calf muscles often occur; muscle pseudohypertrophy and mental retardation do not occur. A cardiomyopathy is common. An X-linked inherited disorder, nonallelic to Duchenne muscular dystrophy. [Alan E. H. Emery, Fritz Dreifuss]