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Duchenne muscular dystrophy
Alternative namesPseudohypertrophic muscular dystrophy; Muscular dystrophy - Duchenne type
DefinitionDuchenne muscular dystrophy is an inherited disorder characterized by rapidly progressive muscle weakness which starts in the legs and pelvis and later affects the whole body.
Causes, incidence, and risk factors
Duchenne muscular dystrophy is a rapidly progressive form of muscular dystrophy . It is caused by a defective gene, but it often occurs in people from families without a known family history of the condition. It is marked by progressive loss of muscle function, which begins in the lower limbs.
The cause of the muscle impairment is an abnormal gene for dystrophin (a protein in the muscles). Duchenne muscular dystrophy is inherited in an X-linked recessive pattern. (Recessive means the trait doesn't occur in the presence of a dominant gene.) This means that women are almost never affected; women normally have two X chromosomes, one of which contains a normal, dominant copy of the gene that will make enough of the protein for them to avoid symptoms. Women who carry the defective gene can pass an abnormal X on to their sons, however. Since boys have an X from their mother and a Y from father, there is no second X to make up for the defective gene from the carrier mother.
The sons of carrier females each have a 50% chance of having the disease, and the daughters each have a 50% chance of being carriers.
Symptoms usually appear before age 6 and may appear as early as infancy. 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 or as early as in the lower half of the body.
Calf muscles initially enlarge -- the enlarged muscle tissue is eventually replaced by fat and connective tissue (pseudohypertrophy). Muscle contractures occur in the legs, rendering the muscles unusable because the muscle fibers shorten and fibrosis occurs in connective tissue.
Muscular weakness and skeletal deformities contribute to frequent breathing disorders. Cardiomyopathy occurs in almost all cases. Intellectual impairment may occur, but it is not inevitable and does not worsen as the disorder progresses.
Duchenne muscular dystrophy occurs in approximately 2 out of 10,000 people. Because this is an inherited disorder, risks include a family history of Duchenne muscular dystrophy. In contrast, Becker muscular dystrophy is a form that progresses much more slowly
Signs and testsMuscle wasting (atrophy) begins in the legs and pelvis, then progresses to the muscles of the shoulders and neck, followed by loss of arm muscles and respiratory muscles. Calf muscle enlargement (pseudohypertrophy) is quite obvious. Cardiomyopathy is commonly present, but signs of congestive heart failure or arrhythmias (irregular heartbeats) are rare. Respiratory disorders are common during the later stages, including pneumonia and aspiration of food or fluid into the lungs.
There is no known cure for Duchenne muscular dystrophy. Treatment is aimed at control of symptoms to maximize the quality of life.
Activity is encouraged. Inactivity (such as bedrest) can worsen the muscle disease. Physical therapy may be helpful to maintain muscle strength and function. Orthopedic appliances (such as braces and wheelchairs) may improve mobility and the ability for self-care.
Support GroupsThe stress of illness can often be helped by joining a support group where members share common experiences and problems. See muscular dystrophy - support group . The Muscular Dystrophy Association is an excellent source of information on this disease.
Expectations (prognosis)Duchenne muscular dystrophy results in rapidly progressive disability. Death usually occurs by age 25, typically from respiratory (lung) disorders.
Calling your health care providerCall your health care provider if symptoms indicate Duchenne muscular dystrophy.
Call your health care provider if symptoms worsen, or new symptoms develop, particularly fever with cough or breathing difficulties .
PreventionGenetic counseling is advised if there is a family history of the disorder. Duchenne muscular dystrophy can be detected with about 95% accuracy by genetic studies performed during pregnancy.
Update Date: 10/25/2002David G. Brooks, M.D., Ph.D., Division of Medical Genetics, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT