TYPES OF MUSCULAR DYSTROPHY

Most types of muscular dystrophy are the result of "different abnormalities in the genes, or blueprints, that produce muscle membrane proteins." Typically, the genetic abnormality is inherited from one or both parents, but in some cases, it develops spontaneously. The genetic abnormality results in the development of muscle membranes with missing or malformed parts, causing muscle deterioration and weakness. The most common types of muscular dystrophy include the following:

Duchenne muscular dystrophy occurs when muscle fibers develop with abnormal dystrophin, a building block of muscle. Duchenne is the most common and the most severe form of the disease, affecting one out of every 3,300 boys. Children usually begin to show symptoms between ages two and five, with rapid muscle weakness first affecting the pelvic muscles. Most children lose the ability to walk by age 12 and are confined to a wheelchair. Over time, children develop progressive muscle weakness in their shoulders, back, arms, legs, and finally their respiratory muscles, resulting in a shortened life span, typically about 20 years.

Becker muscular dystrophy is similar to Duchenne, but it progresses more slowly. Symptoms typically begin during adolescence but can begin as early as age five or as late as age 25. Muscle weakness first occurs in the pelvic muscles, so most children eventually lose the ability to walk. As the disease progresses, they also lose strength in their shoulders and back. Because Becker progresses so slowly, many children with Becker have a normal life span.

Limb-girdle muscular dystrophy symptoms begin between ages five and 30, first affecting either the pelvic muscles or the shoulder and back muscles. As the disease progresses, both areas are affected eventually. The severity of muscle weakness resulting from limb-girdle muscular dystrophy varies from person to person, as does the rate at which muscle weakness progresses. Some people develop only mild conditions, but many develop severe disabilities by middle age.

Facioscapulorhumeral muscular dystrophy can begin at any age but typically first appears during adolescence. Because this form of muscular dystrophy tends to progress slowly, people who are affected usually have a normal life span. Muscle weakness first develops in the face, making it difficult for children to close their eyes, whistle, or puff out their cheeks. The shoulder and back muscles gradually become weak, and those affected find it hard to lift objects or raise their hands over their head. Over time, the legs and pelvic muscles also lose strength. People can develop only minor physical symptoms (for example, sleeping with open eyes) or more profound disabilities.

In rare cases, infants can develop symptoms during their first and second year, resulting in expressionless faces and serious muscle weakness during early childhood.

Congenital muscular dystrophy is a group of disorders. Those affected share two unique characteristics: they have muscle weakness at birth, often causing joint contractures and deformities, and muscle biopsies show nonspecific abnormalities. A combination of the facial, arm and leg, pelvic, respiratory, and shoulder muscles can be weak at birth, but this muscle weakness rarely gets worse. Other types of muscular dystrophy, which are rare, include distal, ocular, oculopharyngeal, and Emery-Dreifuss.