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Duchenne muscular dystrophy (DMD) is a severe type of muscular dystrophy that primarily affects boys.Muscle weakness usually begins around the age of four, and worsens quickly.Muscle loss typically occurs first in the thighs and pelvis followed by the arms. This can result in trouble standing up. Most are unable to walk by the age of 12.Affected muscles may look larger due to increased fat content.Scoliosis is also common.Some may have intellectual disability. Females with a single copy of the defective gene may show mild symptoms.

The disorder is X-linked recessive. About two thirds of cases are inherited from a person's mother, while one third of cases are due to a new mutation.It is caused by a mutation in the gene for the protein dystrophin.Dystrophin is important to maintain the muscle fiber's cell membrane. Genetic testing can often make the diagnosis at birth.[Those affected also have a high level of creatine kinase in their blood.