Most types of muscular dystrophy are caused by different abnormalities in the genes that produce muscle membrane proteins. Although the genetic problem is usually inherited, sometimes it can develop spontaneously.

The genetic abnormality triggers the development of muscle membranes with missing or malformed parts, causing muscle deterioration and weakness. Some types of muscular dystrophy (including Duchenne, the most severe type) are X-linked, which means that the abnormality is carried on the X chromosome that the mother contributes. A girl receives two X chromosomes, one from each parent, whereas a boy receives a Y chromosome from his father and an X from his mother. This means that it is almost always boys who develop symptoms, because girls inherit a normal X chromosome that may cancel out the abnormal one. Girls with such an affected X chromosome carry the MD gene but have no symptoms; however, they have a 50-50 chance of passing the condition to their sons (or carrier status to their daughters).


Many children with muscular dystrophy have had a normal pattern of early development, but eventually symptoms begin to appear. Symptoms can first appear during early childhood or late in adult life, depending on the type of muscular dystrophy.

The child may trip a lot, waddle, have trouble climbing stairs, or walk on toes without touching the heel to the floor. Toddlers may develop a sway-back to compensate for weakening hip muscles. Children may struggle to get up from a sitting position or have trouble pushing objects such as a wagon or a tricycle. Many children also develop enlarged calf muscles as muscle tissue is destroyed and replaced by nonmuscle tissue.

The symptoms of Becker muscular dystrophy are less severe and may start during the school years, so that children live well into adulthood. in contrast, Duchenne muscular dystrophy begins during early childhood and causes fairly rapid weakness.

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