Scapuloperoneal myopathy is a rare genetic disorder characterized by weakness and wasting of certain muscles. Symptoms are usually limited to the shoulder blade area (scapula) and the smaller of the two leg muscle groups below the knee (peroneal). Facial muscles may be affected in a few cases. The leg symptoms often appear before the shoulder muscles become weakened. The rate of progression of the disorder varies from case to case. This condition can also occur in combination with other disorders. Scapuloperoneal myopathy is inherited as an autosomal dominant trait.

Symptoms of scapuloperoneal myopathy primarily include Muscle Weakness and wasting usually limited to muscles in the shoulder blade and girdle area and the legs below the knees. This disorder can begin in childhood or adulthood. The progression rate and severity may vary greatly, with some cases progressing more quickly than others. In most cases, the progression is slow.

The shoulder muscles are affected first, in most cases. In some cases, shoulder involvement may precede lower leg involvement by years or decades. In some cases, lower leg involvement may precede shoulder involvement. In rare cases, some facial muscles may be mildly affected.

Scapuloperoneal myopathy is inherited as an autosomal dominant trait. Human traits including the classic genetic diseases, are the product of the interaction of two genes for that condition, one received from the father and one from the mother.

In dominant disorders, a single copy of the disease gene (received from either the mother or father) will be expressed “dominating” the other normal gene and resulting in the appearance of the disease. The risk of transmitting the disorder from affected parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child.

In some cases, scapuloperoneal myopathy may be due to new genetic changes (mutations) that appear to occur spontaneously for unknown reasons (sporadically).

Investigators have determined that some cases of scapuloperoneal myopathy may be caused by disruption or changes (mutations) of a gene located on the long arm (q) of chromosome 12 (12q13.3-q15). Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p” and a long arm identified by the letter “q.” Chromosomes are further subdivided into bands that are numbered. For example, “chromosome 12q13.3-q15” refers to bands 13.3-15 on the long arm of chromosome 12.

There is no specific treatment for individuals with scapuloperoneal myopathy. Treatment may include specified amounts of therapeutic exercise and physical therapy alternating with periods of rest.

Genetic counseling may benefit affected individuals and their families. Other treatment is symptomatic and supportive.

Scapuloperoneal myopathy affects males and females in equal numbers. Symptoms may begin in childhood or during adulthood. Scapuloperoneal myopathy is a rare disorder; the exact prevalence of this disorder in the general population is unknown.