Muscular dystrophy (MD) refers to a group of more than 30 genetic diseases that cause progressive weakness and degeneration of skeletal muscles used during voluntary movement. The word dystrophy is derived from the Greek dys, which means "difficult" or "faulty," and troph, or "nourish." These disorders vary in age of onset, severity, and pattern of affected muscles. All forms of MD grow worse as muscles progressively degenerate and weaken. Many patients eventually lose the ability to walk.
Some types of MD also affect the heart, gastrointestinal system, endocrine glands, spine, eyes, brain, and other organs. Respiratory and cardiac diseases may occur, and some patients may develop a swallowing disorder. MD is not contagious and cannot be brought on by injury or activity.