Mutations in the dystrophin gene cause Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD),1, 2 characterized by a progressive skeletal muscle degeneration, weakness, loss of ambulation, and early death due to cardiorespiratory insufficiency.3 The absence of dystrophin causes DMD, whereas mutations resulting in a reduced amount or shortened dystrophin protein cause BMD. Here, DMD is linked to Becker muscular dystrophy.