What types of muscular dystrophy are there?
Muscular dystrophy is a group of inherited diseases that are characterized by weakness and wasting away of muscle tissue, with or without the breakdown of nerve tissue. There are nine types of muscular dystrophy, but in each type there is an eventual loss of strength, increasing disability, and possible deformity. There are several major forms of muscular dystrophy
that affect teens, each of which weakens different muscle groups in various ways.
Duchenne muscular dystrophy (DMD): Duchenne muscular dystrophy is caused by a defective gene (segment of DNA) inherited on the X chromosome. It primarily affects boys and is the most severe type. It is the most severe form of muscular dystrophy. DMD occurs in about 1 in 3,500 male births, and affects approximately 8,000 boys and young men in the United States. A milder form occurs in very few female carriers.
Becker muscular dystrophy (BMD): Becker-type muscular dystrophy is linked to the X chromosome, affects dystrophin production, and occurs in males. However, the illness is about 10 times rarer than Duchenne, and it produces milder symptoms. Some people seem to have a form of disease that is intermediate in severity between Duchenne and Becker-type. BMD affects older boys and young men, following a milder course than DMD. BMD occurs in about 1 in 30,000 male births.
Facioscapulohumeral muscular dystrophy (FSH): Facioscapulohumeral muscular dystrophy occurs in both sexes, and it often strikes several members of the same family. However, because the symptoms vary in intensity, family members may have such mild forms of the illness that they are unaware of any muscle problems. Weakness of the facial muscles and the shoulder is typical. FSH, also known as Landouzy-Dejerine disease, begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles of the face, shoulders, and upper arms.
Emery-Dreifuss muscular dystrophy (EDMD): EDMD affects young boys, causing contractures and weakness in the calves, weakness in the shoulders and upper arms, and problems in the way electrical impulses travel through the heart to make it beat (heart conduction defects). Fewer than 300 cases of EDMD have been identified.
Limb-girdle muscular dystrophy (LGMD): LGMD begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles around the hips and shoulders. It is the most variable of the muscular dystrophies, and there are several different forms of the disease now recognized. Many people with suspected LGMD have probably been misdiagnosed in the past, and therefore the prevalence of the disease is difficult to estimate. The number of people affected in the United States may be in the low thousands.
Myotonic dystrophy: Myotonic muscular dystrophy can occur in both sexes and is the most common form of adult muscular dystrophy, with symptoms often starting in adolescence. Also known as Steinert's disease, it affects both men and women, causing generalized weakness first seen in the face, feet, and hands. It is accompanied by the inability to relax the affected muscles (myotonia). Symptoms may begin from birth through adulthood. It is the most common form of muscular dystrophy, affecting more than 30,000 people in the United States.
Oculopharyngeal muscular dystrophy (OPMD): OPMD affects adults of both sexes, causing weakness in the eye muscles and throat. It is most common among French Canadian families in Quebec, and in Spanish-American families in the southwestern United States.
Distal muscular dystrophy (DD): DD begins in middle age or later, causing weakness in the muscles of the feet and hands. It is most common in Sweden, and rare in other parts of the world.
Congenital muscular dystrophy (CMD): CMD is present from birth, results in generalized weakness, and usually progresses slowly. A subtype, called Fukuyama CMD, also involves mental retardation. Both are rare; Fukuyama CMD is more common in Japan.