What is Myotonic Dystrophy

Myotonic dystrophy is an inherited type of muscular dystrophy that affects the muscles and other body systems. People who have myotonic dystrophy have muscle wasting and weakness in their lower legs, hands, neck and face that get worse over time. Signs and symptoms of myotonic dystrophy usually develop when a person is in his or her twenties or thirties. The severity of myotonic dystrophy varies widely among those who have it, even among family members.

The weakness and muscle wasting that occurs slowly progress to the point of disability. Usually, disability does not become severe until fifteen to twenty years after the symptoms appear. The progression of muscle weakness is slower and is less serious in people who are older when the muscle weakness is first noticed.

There are two types of myotonic dystrophy: Type 1 and Type 2. The two types are caused by alterations (mutations) in two different genes. The symptoms of Type 2 myotonic dystrophy are usually milder than those of Type 1. A severe type of Type 1 myotonic dystrophy can be seen at birth. This form of Type 1 is called congenital myotonic dystrophy. Congenital myotonic dystrophy has only been seen in Type 1 myotonic dystrophy and not in Type 2.

Myotonic dystrophy is the most common form of muscular dystrophy that begins in adulthood. It affects about 1 in 8,000 people worldwide. Type 1 myotonic dystrophy is the most common form in most countries. The commonness of the two types depends upon a person's ethnic background. For example, Type 2 myotonic dystrophy is as common as Type 1 in people who have German ancestry.