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|Becker Muscular Dystrophy|
Becker muscular dystrophy (Becker MD) is closely related to Duchenne MD but less severe. Both are caused by mutations in the DMD gene, which makes the protein dystrophin. Persons with Becker MD have partial but insufficient function of dystrophin. The disorder usually appears around age 11 but may occur as late as age 25, and patients generally live into middle age or later. The rate of progressive, symmetric (on both sides of the body) muscle atrophy and weakness varies greatly among affected individuals. Many patients are able to walk until they are in their mid-thirties or later, while others are unable to walk past their teens. Some affected individuals never need to use a wheelchair. As in Duchenne MD, muscle weakness in Becker MD is typically noticed first in the upper arms and shoulders, upper legs, and pelvis.
Early symptoms of Becker MD include walking on one's toes, frequent falls, and difficulty rising from the floor. Calf muscles may appear large and healthy as deteriorating muscle fibers are replaced by fat, and muscle activity may cause cramps in some people. Cardiac and mental impairments are not as severe as in Duchenne MD.