Wednesday, September 7, is World Duchenne Muscular Dystrophy (DMD) Awareness Day. DMD is the most common and most severe form of muscular dystrophy, a group of genetic diseases characterized by progressive muscle weakness and degeneration of the skeletal muscles. Found almost exclusively in boys, DMD is caused by a mutation on a gene located on the X chromosome that is responsible for producing a muscle-protecting protein called dystrophin.