Muscular dystrophy is a group of genetic diseases that cause progressive weakness and loss of muscle mass. The condition is caused by mutations in a persons genes that interfere with the production of proteins that strengthen and protect muscles. There are more than 30 types of muscular dystrophy, each with somewhat different symptoms. Some types of muscular dystrophy are defined by a specific feature or by where in the body symptoms begin. The main sign of muscular dystrophy is progressive muscle weakness, and specific signs and symptoms begin at different ages and in different muscle groups, depending on the type of muscular dystrophy. Duchenne type muscular dystrophy is the most common form, and it usually affects boys in early childhood. Some types of muscular dystrophy are present at birth or become evident before age 2. The complications of progressive muscle weakness include trouble walking, and some people with muscular dystrophy eventually need to use a wheelchair. There is no cure for muscular dystrophy, but treatment can help manage many of the symptoms.