- muscular dystrophy
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a hereditary disease characterized by gradual wasting of the muscles with replacement by scar tissue and fat, sometimes also affecting the heart.[1865-70]
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Inherited disease that causes progressive weakness in the skeletal (and occasionally heart) muscle.Muscle tissue degenerates and regenerates randomly and is replaced by scar tissue and fat. There is no specific treatment. Physical therapy, braces, and corrective surgery may help. Duchenne muscular dystrophy, the most common, strikes only males. Symptoms, including frequent falls and difficulty in standing up, start in boys 3–7 years old; muscle wasting progresses from the legs to the arms and then the diaphragm. Pulmonary infection or respiratory failure usually causes death before age 20. The gene can now be detected in female carriers and male fetuses. Becker dystrophy, also sex-linked, is less severe and begins later. Patients remain able to walk and usually survive into their 30s and 40s. Myotonic muscular dystrophy affects adults of both sexes, with myotonia and degeneration two to three years later, along with cataracts, baldness, and gonadal atrophy. Limb-girdle dystrophy affects the pelvic or shoulder muscles in both sexes. Facioscapulohumeral (face, shoulder-blade, and upper-arm) dystrophy starts in childhood or adolescence and affects both sexes; after initial symptoms of difficulty raising the arms, the legs and pelvic muscles can be affected; the main facial effect is difficulty in closing the eyes. Life expectancy is normal.* * *
hereditary disease that causes progressive weakness and degeneration of the skeletal muscles (muscle). Of the several types of muscular dystrophy, the more common are Duchenne, facioscapulohumeral, Becker, limb-girdle, and myotonic dystrophy. In all of these there is usually early evidence of degeneration and then regeneration of some muscle fibres. Those fibres that regenerate become larger than normal, and eventually the muscles are totally replaced by fibrous scar tissue and fat.Duchenne muscular dystrophy is the most common childhood form of the disease; 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 that results in the failure of the body to produce a functional muscle protein called dystrophin. 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. Early symptoms, which usually occur between the ages of two and six, include a waddling gait, frequent falling, difficulty in getting up from a lying or sitting position, enlargement of the calf muscles, inability to raise the knees, and disappearance of a normal knee or ankle jerk; symptoms become more obvious as the child ages. Stairs eventually become impossible to climb, and by early adolescence the child is unable to walk. Muscle wasting progresses upward from the legs, and the arms are eventually affected. Ultimately, muscle wasting affects the muscles of the diaphragm, and breathing becomes shallow. Life-threatening pulmonary infections or respiratory failure usually occurs before the age of 20. Genetic testing can reliably detect the Duchenne gene in female carriers and in affected male fetuses.Becker muscular dystrophy has symptoms similar to Duchenne but begins in later childhood or adolescence and progresses more slowly. It is also a sex-linked disorder that is caused by a defective gene on the X chromosome; however, some functional dystrophin is produced. Individuals with this form of muscular dystrophy may function well into adult life, with certain limitations.Limb-girdle dystrophy (dystrophy of the pelvic or shoulder muscles) affects both sexes. The first symptoms are manifest in the pelvic region, starting in late childhood. Muscular weakness eventually progresses to the arms and legs. Symptoms include frequent falling, difficulty in climbing, and a waddling gait.Facioscapulohumeral dystrophy (dystrophy related to the face, the shoulder blade, and the upper arm) starts in adolescence and affects both sexes. The first symptom may be difficulty in raising the arms. Later symptoms may include weakness of the legs and pelvic girdle, forward sloping of the shoulders, and difficulty in closing the eyes. This form of muscular dystrophy can range in severity; individuals with facioscapulohumeral dystrophy may be mildly affected or totally disabled.Myotonic muscular dystrophy is the most common form of the disease affecting adults. The primary symptom is myotonia, a stiffening of the muscles after use. Myotonic muscular dystrophy may also affect the central nervous system (nervous system, human), heart, gastrointestinal tract, eyes (eye, human), and endocrine glands. Because of the possibility of serious cardiac complications, individuals with this form of muscular dystrophy may require a pacemaker. Myotonic muscular dystrophy type 1 and myotonic muscular dystrophy type 2 are both caused by a genetic mutation, albeit on different chromosomes, that results in defective RNA, the molecule that translates DNA into proteins. Genetic testing can detect these mutations in persons suspected to have the disease.There is no specific cure or treatment for muscular dystrophy. Physical therapy, exercises, splints, braces, and corrective surgery may help relieve some of the symptoms. Corticosteroid medications may slow the progression of the disease.* * *
Universalium. 2010.
