Muscle biopsy involves the removal of a small piece of muscle for examination. Since the discovery of the defect of dystrophin in DMD it has also been possible to arrange for muscle biopsy specimens to be examined for this specific defect. The worsening of disability can be slowed by such measures as physiotherapy, but it cannot be stopped. On average, use of a wheelchair proceeds from occasional use at about age 9 years to almost total dependence by the early teens, but there is a range of severity to either side of this. As the ability to walk is lost, the function of the hands and arms becomes increasingly important in determining the affected person's abilities.
Most affected people survive into their twenties.
A small minority survive only to their late teens, another small number to more than 30 years of age. Some people with DMD have additional problems. These include impaired intellectual development and problems with the joints, the spine, the heart and the function of the lungs. Intellectual handicap is more frequent in boys with DMD than in the general population but only affects a minority. Unlike the muscle weakness, it is not progressive.