DMD and Duchenne muscular dystrophy: Becker muscular dystrophy (BMD), Online Mendelian Inheritance in Man (OMIM) #300376, is a neuromuscular disorder caused by variants in the Duchenne muscular dystrophy (DMD) gene, which allow the expression of abnormal and/or quantitatively defective dystrophin protein in skeletal muscle fibers.1 Such variants are most commonly in-frame deletions of 1 or more DMD exons, but also include in-frame duplications, small insertion/deletions, missense, intronic, and nonsense variants.2,3