Duchenne muscular dystrophy (DMD) is characterized by weakness of leg, pelvic and shoulder girdle muscles starting in early childhood. Becker muscular dystrophy (BMD) is a milder variant of DMD with a better prognosis, with a mean age of onset at 11 years. X-linked dilated cardiomyopathy (XLCM) is a rare disorder with rapidly progressive cardiomyopathy but almost no skeletal muscle impairment. Absence of the dystrophin protein (DMD) and reduced levels or abnormal configuration of dystrophin (BMD) leads to membrane fragility making muscle cells susceptible to damage from contraction. Secondary increase in free radicals and activation of calcium-dependent proteases are thought to further contribute to muscle degeneration.
