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 severely 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 slowly progressive muscle degeneration, with increasing weakness and wasting (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. Because FSHD is a disease that usually progresses very slowly and rarely affects the heart or respiratory system, it isn’t considered life-threatening. Most people with the disease have a normal life span.
What causes FSHD?
FSHD is almost always associated with a genetic mistake (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 interferes with the correct processing of genetic material. Recent research has found that the abnormally short DNA segment prevents a molecular “braking system” from operating. Without the braking system, cells make proteins they’re not supposed to make. (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.) When scientists first discovered the missing chromosome 4 DNA, they thought it might lie inside a gene that carried instructions for a muscle protein. Later, when no such gene was found, they surmised that the loss of the DNA might affect neighbouring genes — that these neighbouring genes, needed by muscle, were perhaps being switched off by the DNA alteration. Today, scientists think the missing DNA section on chromosome 4 may allow neighbouring genes to switch on and be used for protein manufacturing even though they would normally be switched off in muscle cells. If this theory is true, then the problem in FSHD muscles is one of too many, rather than too few, proteins in FSHDaffected muscles.
