MUSCULAR DYSTROPHY

inherited disease that causes increasing weakness in muscle tissue. The muscles affected are the skeletal muscles and, occasionally, the muscles of the heart. Of the several types of dystrophy, the more common are Duchenne's, facioscapulohumeral (dystrophy related to the face, the shoulder blade, and the upper arm), Becker's, limb-girdle, and myotonic dystrophy (see myotonia). In all of these the muscle tissue seems to be affected in a random fashion. There is usually early evidence of degeneration and then regeneration of some muscle fibres. Those that regenerate become larger than normal, and eventually the muscles are totally replaced by fibrous scar tissue and fat. Duchenne's muscular dystrophy is the most common of the dystrophies. It occurs in one of every 3,300 male births. It is a sex-linked disorder, meaning that it strikes males almost exclusively. The disease is caused by a defective gene on the 23rd, or X, chromosome. Most females who carry the genetic defect are unaffected, but they have a 50 percent probability of passing the disease to each of their sons. There are no obvious symptoms in the first year of life. When the child begins to walk there are minor abnormalities in his gait: he tends to waddle and to walk on the toes and has difficulty in getting up once he has fallen and in raising his knees, which prevents running. The symptoms become more obvious as the child ages; by the age of five years there is enlargement of the calf muscles, difficulty in getting up, inability to run, and disappearance of a normal knee or ankle jerk. Stairs eventually become impossible to climb, and by early adolescence the child is unable to walk. The muscle wasting progresses upward from the child's legs, and the arms are eventually affected. Ultimately the muscle wasting affects the muscles of the diaphragm; breathing becomes shallow and pulmonary infections become a constant hazard. Infections or respiratory failure usually bring about death before the age of 20. Researchers have developed genetic markers that can reliably detect the Duchenne's gene in female carriers and in affected male fetuses. Becker's dystrophy has symptoms much the same as Duchenne's but begins in later childhood or adolescence and is generally not so devastating. Some victims can function well into adult life with certain limitations. Limb-girdle dystrophy (dystrophy of the pelvic or the shoulder muscles) affects both sexes. The first symptoms are manifest in the pelvic region, starting in late childhood. There are frequent falls, difficulty in climbing, and a waddling gait. Facioscapulohumeral dystrophy starts in adolescence. The affected person may be mildly affected or may be totally disabled. The first symptom may be difficulty in raising the arms. Weakness can also affect the legs and pelvic girdle. The main effect on the facial muscles is difficulty in closing the eyes. There is no specific treatment for muscular dystrophy. Physical therapy, exercises, splints, braces, and corrective surgery may help.