Duchenne muscular dystrophy is the most severe form of muscular dystrophy in children, as well as the most common. Duchenne muscular dystrophy and its milder phenotype, Becker muscular dystrophy, are called dystrophinopathies as they are caused by mutations in the gene DMD, which encodes for the protein dystrophin. The DMD gene is the largest yet identified gene in humans and is located on the short arm of the X chromosome. Dystrophin serves as a vital cytoplasmic protein that connects muscle fiber cytoskeleton to the extracellular matrix. The phenotype of the dystrophinopathy depends upon the amount of residual dystrophin protein. In the most severe phenotype, which is Duchenne muscular dystrophy, the dystrophin is either completely absent or very minimal in amount.