A 10-year-old boy apparently normal at bih had delayed walking and had difficulty in walking. As years passed, weakness increased and now is wheelchair bound. What is your diagnosis

Boys with Duchenne muscular dystrophy are normal at bih. Very early motor milestones are met, but walking is often delayed. The first indications of muscle weakness are clumsiness and inability to keep up with peers. Weakness begins in the pelvic girdle muscles and then extends to the shoulder girdle. Enlargement of the muscles of the lower leg associated with weakness, termed pseudohyperophy, is often present. The mean age of wheelchair dependence is around 9.5 years.Duchenne and Becker muscular dystrophy are caused by loss-of-function mutations in the dystrophin gene on the X chromosome. Duchenne muscular dystrophy is typically associated with deletions or frameshift mutations that result in the total absence of dystrophin. In contrast, the mutations in Becker muscular dystrophy typically permit the synthesis of a truncated version of dystrophin, which presumably retains some function. Hence is less severe.Robbins pathology 9e pg: 1242