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, which means nourish. These disorders vary in the age of onset, severity, and the pattern of affected muscles. All forms of MD grow worse as muscles progressively degenerate and weaken. The majority of patients eventually lose the ability to walk.
Some types of MD also affect the heart, the gastrointestinal system, endocrine glands, the spine, the eyes, the brain, and other organs. Respiratory and cardiac diseases are common, and some patients may develop a swallowing disorder. MD is not contagious and cannot be brought on by injury or activity.
This answer is based on source information from the National Institute of Neurological Disorders and Stroke.