Facioscapulohumeral muscular dystrophy (FSHD) is the most prevalent form of muscular dystrophy affecting men, women and children.  It is an autosominal dominant type of muscular dystrophy that causes progressive muscle wasting and weakness.  The disease initially affects the muscles of the face (facio), shoulder (scapulo), and upper arms (humeral).  The degeneration of muscle can also spread to the back, pelvis and legs.

FSHD affects approximately 1 in 20,000.  Estimating the incidence at about 25,000 Americans.  Through genetic testing and fewer misdiagnosis, the incidence will probably prove to be much higher.  FSHD has been linked to the D4Z4 region of Chromosome 4.  Although approximately two-thirds of cases are inherited, up to one-third are a result of a spontaneous mutation, meaning that neither parent of the affected individual has the disease.