Duchenne muscular dystrophy (DMD) is a severe type of muscular dystrophy. The symptom of muscle weakness usually begin around the age of four in boys and worsens quickly. Typically muscle loss occurs first in the upper legs and pelvis followed by those of the upper arms. This can result in trouble standing-up. Most are unable to walk by the age of twelve. 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.