Duchenne muscular dystrophy is an inherited disorder of the muscles. It causes the muscles to degenerate and lose their function.

What is going on in the body?

Duchenne muscular dystrophy occurs in about 1 in 3500 males. There is a family history in 70% of affected people. The disorder is present at birth, but usually doesn't become apparent until 3 to 5 years of age. Affected children may fall frequently and have difficulty keeping up with playmates. Running, jumping, and hopping are abnormal. The calf muscles are unusually large.

By 5 to 6 years of age, the enlarged muscle is replaced by fat and connective tissue. Muscle weakness is obvious. Affected children use their hands to rise from a sitting position. This is because the muscles nearest the hips weaken before the lower leg muscles. Legs are more severely affected than arms. Tendons around the heels tighten, which causes affected children to walk on their toes.

Between 8 and 10 years of age, tendons tighten around the hips, knees, elbows, and wrists. Braces may be needed.

By 12 years of age, the child is usually using a wheelchair. Curvature of the spine begins. With time, the curvature and weakening chest muscles impair lung function.

By 16 to 18 years of age, breathing is so weak that lung infections or aspiration of food become problems. Such problems are the common causes of death.

The heart muscle becomes enlarged in almost all affected people. Heart problems are not common causes of death, though. Intellectual impairment is common and does not seem to get worse over time. The reason for the intellectual impairment is not known.

What are the causes and risks of the disease?

The risk of developing Duchenne muscular dystrophy depends on a variety of genetic factors.