Duchenne muscular dystrophy is one of the most frequently encountered genetic diseases, affecting one in every 3500 males born in America, but much less commonly in females. Muscular dystrophy is associated with the progressive degeneration of skeletal and cardiac muscle fibers, weakening the muscles and leading ultimately to death from respiratory or cardiac failure. The symptoms become evident at about 2 to 6 years of age, and most affected individuals do not survive much beyond the age of 20. In boys with Duchenne muscular dystrophy, the muscles of the hip girdle and trunk are the first to weaken, requiring patients to use their arms to climb up the legs in attempting to go from lying to standing.
The recessive gene responsible for a major form of muscular dystrophy (Duchenne muscular dystrophy) has been identified on the X chromosome, and muscular dystrophy is a sex-linked recessive disease. This gene codes for a protein known as dystrophin, which is either absent (or present in a nonfunctional form in patients with the disease). Dystrophin is a large protein that links cytoskeletal proteins to membrane glycoproteins. It resembles other known cytoskeletal proteins and may be involved in maintaining the structural integrity of the plasma membrane or of elements within the membrane, such as ion channels, in fibers subjected to repeated structural deformation during contraction. Preliminary attempts are being made to treat the disease by inserting the normal gene into dystrophic muscle cells.