MUSCULAR DYSTROPHY

Muscular dystrophy (MD) is a group of inherited diseases in which the muscles that control movement (called voluntary muscles) progressively weaken. In some forms of this disease, the heart and other organs are also affected.

There are nine major forms of muscular dystrophy:

  • Myotonic
  • Duchenne
  • Becker
  • Limb-girdle
  • Facioscapulohumeral
  • Congenital
  • Oculopharyngeal
  • Distal
  • Emery-Dreifuss

MD can occur at different ages of a person’s life, ranging from infancy to middle age or later. The type of the disease is based in part on when in a person’s life MD appears, as well as the severity of the muscle weakness, which muscles are affected, the rate of symptom progression, and the way the disease arises. Some forms affect only males; others affect both males and females. Some sufferers still enjoy a normal life span with mild symptoms that progress very slowly, while others experience fast and severe muscle weakness and wasting, dying in their late teens to early 20s.

The various types of MD affect more than 50,000 Americans. Through advances in medical care, children with muscular dystrophy are living longer than ever before.

Until the 1980’s little was known about the cause of any type of muscular dystrophy. We now know that MD is caused by defects in certain genes. The type of MD is determined by which gene is defective. In 1986, researchers discovered the gene that, when defective or flawed, causes Duchenne muscular dystrophy. In 1987, the muscle protein associated with this gene was called dystrophin. Duchenne MD occurs when that gene fails to make dystrophin. Becker MD occurs when a different mutation in the same gene results in having some dystrophin, but it’s either not enough or it’s poor in quality. Scientists have discovered and continue to search for the genetic defects that cause other forms of muscular dystrophy.

Most of the muscular dystrophies are a form of inherited disease called X-linked disorders or genetic diseases that mothers can transmit to their sons even though the mothers themselves are unaffected by the disease.

Men carry one X chromosome and one Y chromosome. Females carry two X chromosomes. Thus, in order for a girl to become affected by muscular dystrophy, both of her X chromosomes would have to carry the defective gene — an extremely rare occurrence, since her mother would have to be a carrier (one defective X chromosome) and her father would have to have muscular dystrophy (since men carry just one X chromosome, the other is a Y chromosome.)

A female who carries the defective X chromosome can pass the disease to her son (whose other chromosome is a Y, from the father).

A few muscular dystrophies aren’t inherited at all and occur because of a new gene abnormality or mutation.

Sources: The Mayo ClinicMuscular Dystrophy AssociationNational Institute of Arthritis and Musculoskeletal and Skin Diseases