Facioscapulohumeral muscular dystrophy (FSHD) is a genetic muscle disorder in which the muscles of the face, shoulder blades and upper arms are among the most affected.
The long name comes from facies, the Latin word and medical term for face; scapula, the Latin word and anatomical term for shoulder blade; and humerus, the Latin word for upper arm and the anatomical term for the bone that goes from the shoulder to the elbow.
The term muscular dystrophy means progressive muscle degeneration, with increasing weakness and atrophy (loss of bulk) of muscles. In FSHD, weakness first and most seriously affects the face, shoulders and upper arms, but the disease usually also causes weakness in other muscles.
FSHD usually begins before age 20, with weakness and atrophy of the muscles around the eyes and mouth, shoulders, upper arms and lower legs. Later, weakness can spread to abdominal muscles and sometimes hip muscles.
Some experts divide FSHD into adult-onset and infantile-onset forms. The adult-onset (which includes FSHD that begins in adolescence) is far more common.
In either type of FSHD, facial weakness can start in childhood. Occasionally, other FSHD symptoms appear in early childhood. Infantile-onset FSHD generally runs a more pronounced course with regard to muscle weakness and sometimes also affects hearing and vision. Preliminary evidence suggests that the infantile-onset form is associated with a larger piece of missing DNA. For more, see Signs and Symptoms.
FSHD may be inherited through either the father or the mother, or it may occur without a family history. It is almost always associated with a genetic flaw (mutation) that leads to a shorter than usual segment of DNA on chromosome 4. The segment isn’t part of any particular gene, but it nevertheless seems to interfere with the correct processing of genetic material.
A small number of people have a disorder that looks exactly like FSHD but don’t have the short segment on chromosome 4. The genetic cause of their disorder has yet to be identified.
FSHD usually progresses very slowly and rarely affects the heart or respiratory system. Most people with the disease have a normal life span.
In 2009, MDA-supported researchers found that pieces of a gene called DUX4 are abnormally activated in FSHD-affected cells, leading to production of potentially toxic proteins. Blocking the erroneously activated genes or the proteins made from them seems a likely pathway for the eventual treatment of FSHD. For more, see Research.