Muscular dystrophy, the group of rare genetic diseases that leads to weakening and deterioration of muscles, is caused by genetic mutations. The mutations slow or stop the production of proteins needed to protect muscles. Without the protein, muscle fibers weaken and atrophy. As a result, children with muscular dystrophy have difficulty controlling their arms, legs, torso, and face. Almost all eventually end up in a wheelchair.
The genetic mutations are mostly inherited, but some occur spontaneously in people with no family history of the diseases. The defective genes are present at birth, but Duchenne muscular dystrophy, the most common type, usually isn't diagnosed until around age 3 to 5, when a child's physical impairments become more obvious, says Darryl De Vivo, M.D., pediatric neurologist in the Pediatric Neuromuscular Disease Center at Columbia University Medical Center/New York-Presbyterian.
There are dozens of types of muscular dystrophy. Each one is caused by a different defective gene. In Duchenne muscular dystrophy, the mutation affects the gene that makes dystrophin, a protein that promotes muscle strength. Without dystrophin, the muscles quickly lose mass and weaken. Most sufferers need a wheelchair within 10 years of the first symptoms.
The mutation for Duchenne muscular dystrophy is on the X chromosome. It is usually passed down by the mother, who typically has no symptoms. Boys are almost exclusively affected, as they have only one X chromosome. Girls rarely show symptoms because they have two XX chromosomes, just one of which is usually affected. In almost all female cases, the healthy dystrophin gene on one X chromosome takes over for defective dystrophin gene on the other X chromosome.
Researchers are working on genetic therapies to lessen the effects of several forms of muscular dystrophy. In Duchenne muscular dystrophy, some of the drugs in development hold the promise of reducing the disease's effects to resemble a similar but milder version called Becker muscular dystrophy. "We're seeing a lot of encouraging potential therapies in the pipeline," says Valerie A. Cwik, M.D., executive vice president and chief medical and scientific officer of the Muscular Dystrophy Association in Tucson. "We need to keep moving research forward because we want nothing more than for safe and effective therapies to be made available to all patients at the earliest moment possible."
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