Becker's muscular dystrophy

Alternative names:

benign pseudohypertrophic muscular dystrophy

Definition:

An inherited disorder characterized by slowly progressive muscle weakness of the legs and pelvis.

Causes, incidence, and risk factors:

Becker's muscular dystrophy is very similar to Duchenne's muscular dystrophy, except that it progresses at a much slower rate. The disorder is inherited with an X-linked recessive inheritance pattern--the gene is located on the X chromosome. Men will develop symptoms if the female transmits the gene for the disorder. Women may be carriers of the gene.

There is progressive muscle weakness of the legs and pelvis which is associated with a loss of muscle mass (wasting). Muscle weakness also occurs in the arms, neck, and other areas, but not as severely as in the lower half of the body. Calf muscles initially enlarge (an attempt by the body to compensate for loss of muscle strength), the enlarged muscle tissue is eventually replaced by fat and connective tissue (pseudohypertrophy). Muscle contractures occur in the legs and heels, causing inability to use the muscles because of shortening of muscle fibers and fibrosis of connective tissue. Bones develop abnormally, causing skeletal deformities of the chest and other areas. Cardiomyopathy occurs in almost all cases. Mental retardation may accompany the disorder but it is not inevitable and does not worsen as the disorder progresses. The cause of this impairment is unknown.

Becker's muscular dystrophy occurs in approximately 3 out of 100,000 people. Symptoms usually appear in men between the ages of 7 and 26. Women rarely develop symptoms. Because this is an inherited disorder, risks include having a family history of Becker's muscular dystrophy.