X-linked recessive muscle disease caused by an inability to synthesize dystrophin, which is involved with maintaining the integrity of the sarcolemma; muscle fibers undergo a process that features degeneration and regeneration; clinical manifestations include proximal weakness in the first few years of life, pseudohypertrophy, cardiomyopathy and an increased incidence of impaired mentation; Becker muscular dystrophy is a closely related condition featuring a later onset of disease (usually adolescence) and a slowly progressive course.