A category of inherited, incurable, and often life-threatening diseases in which the limb and trunk muscles deteriorate.

The major types of muscular dystrophy (MD) are Duchenne, limb-girdle, facioscapulohumeral (FSH), Becker, and myotonic. In the United States, 250,000 people are affected by muscular dystrophy, with boys disproportionally represented at the rate of one in every 4,000 births.

Duchenne, the most severe form of muscular dystrophy, is passed exclusively by a defective gene in the mother to her son. A woman with the defective gene has a 50% chance of bearing a son with Duchenne muscular dystrophy. Female children of carrier mothers have a 50% chance of being carriers themselves. In this disease, the muscles of the lower body and spine are affected first; onset is in early childhood between the ages of two and six years. Nearly one-half of all Duchenne victims do not walk until after they reach 18 months old...