The term muscular dystrophy refers to any condition in which healthy muscle cells die and are replaced by fat and connective tissue. The result of this change is a weakening and wasting of muscles that progress over time. Eventually a person with this condition loses all control over his or her muscles, is no longer able to walk, and eventually dies of respiratory failure. Most patients do not live beyond the age of 30.

At least seven distinct forms of muscular dystrophy are known: Duchenne, facioscapulohumoral, limb-girdle, distal myopathy, ocular myopathy , myotonic, and Werdnig-Hoffman. All are hereditary disorders, although the genetic mechanisms by which they are transmitted differ from type to type.

The most common and most severe form of muscular dystrophy is named for a French neurologist, Guillaume B. A. Duchenne (1806-1875), who first described the disorder in 1861. Our current understanding of Duchenne muscular dystrophy is...