APA Dictionary of Psychology

any of a group of inherited disorders marked by degeneration of the muscles, which gradually weaken and waste away due to abnormalities in the muscle structural protein dystrophin and in a series of glycoproteins that are critical to maintaining the structural integrity of muscle fibers. There are various kinds of muscular dystrophy, each differentiated by pattern of inheritance, age of onset, rate of progression, and distribution of weakness. One of the most common and severe types is Duchenne muscular dystrophy (pseudohypertrophic muscular dystrophy). This is inherited as a sex-linked recessive trait and is therefore restricted to boys. It typically begins before the age of 6 with delayed walking and loss of muscle strength, first in the pelvic girdle followed by weakness in the shoulder girdle. Individuals with this disorder have difficulty in rising to a standing position and often fall. They usually are unable to walk by the age of 12 and frequently die from complications before the age of 20.