At least 1 in 3000 people is affected by a serious inherited neuromuscular disorder; muscular dystrophy makes up an appreciable amount of these. (Azofeifa,1995).
Muscular Dystrophy is a heterogeneous group of inherited disorders characterized by progressive muscle wasting and weakness. There are six types of muscular dystrophy: Duchenne muscular dystrophy (DMD), Becker muscular dystrophy, Limb girdle, fasioscapulohumeral, distal, and oculopharyneal.
Duchenne type muscular dystrophy (also known a Meryon's disease) is the most common form of dystrophy. It mainly only effects boys because it is inherited as an X linked recessive trait. It is probably the most serious form of dystrophy there is because it causes most boys to start using a wheel chair by the age of 12 and causing them to die by there 20's. This disease causes some of the boys to have some degree of intellectual impairment. ( Kunkle, 1985) (Murray,1982).
Becker type muscular dystrophy is a lot alike with Duchenne but milder. The onset of this does not occur until they're teenage years and early 20's. Later in life they may lose the ability to walk, but they live until their middle ages and beyond (Murray,1982).
Over the past couple of years clinical features of weakness of the facial, scapulohumeral, anterior tibial, and pelvic girdle muscle have been extended to include retinal vascular disease, sensory hearing loss and, in severe cases, even abnormalities of the central nervous system. Most people are only mildly affected by this but many become dependent on wheelchairs later on in life. This is condition is inherited as an autosomal dominant trait. In 1990 the gene that is responsible was located on chromosome 4.14 restriction enzyme DNA fragments associated with the gene have been found to be greater than 35 kilobases in length in people who do not have muscular dystrophy. Then the people who are affected are always less than this (measured on an electrophoretic gel).