An X-linked recessive disorder (that is, the abnormal gene is carried on the X chromosome – see CHROMOSOMES). This means that the disease occurs almost exclusively in males, as its presence in a female is counteracted by the normal gene likely to be in her other X chromosome. The disorder involves progressive muscular weakness and wasting. It is the most common form of muscular dystrophy, occurring in 30 per 100,000 live male births, often – but not always – in families with other members having the disorder.

The disease usually appears within the first three years of life, beginning in the pelvic girdle and lower limbs and later spreading to the shoulder girdle. The calf muscles become bulky (pseudohypertrophy). This weakness gives rise to a characteristic waddling gait and, when rising from the supine position, the child rolls on to his face and then uses his arms to push himself up. Death usually occurs by the middle of the second decade from respiratory infections. Prenatal screening of possible female carriers (concerned as they have family members with the condition) is available using gene probes. (See DYSTROPHY; MUSCLES, DISORDERS OF – Myopathy.)