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An X-linked recessive muscular dystrophy that may present in children or adults. The disease is characterized by a clinical triad: (1) CONTRACTURE of the elbows, ACHILLES TENDON, and posterior cervical muscles; (2) slowly progressive muscle atrophy and weakness; and (3) a cardiomyopathy usually presenting as an atrioventricular block (HEART BLOCK). The weakness initially affects the upper arm and chest muscles, followed by pelvic and leg muscle paresis. Sudden death (DEATH, SUDDEN, CARDIAC) may occur as the result of the cardiac conduction defect. (Adams et al., Principles of Neurology, 6th ed, p1419; Curr Opin Neurol 1997;10 (5):421-425)