Duchenne and Becker Muscular Dystrophies

This patient's age, speech delay, bilateral lower-extremity weakness, apparent increase in calf diameter, and history of a wheelchair-bound uncle are typical of Duchenne muscular dystrophy (DMD). DMD is the most common muscular dystrophy of childhood that affects boys who have inherited a defective dystrophin gene on X-chromosome p21. Weakness begins in the proximal lower-extremity muscles and manifests as difficulty walking, running, jumping, and climbing stairs. Boys may push their arms on their thighs (Gower sign) to transition from sitting to standing.