Facioscapulohumeral muscular dystrophy (FSHD) is a common hereditary disease of muscle. Patients with FSHD have a chromosomal rearrangement within the subtelomeric region of chromosome 4 (4q35). This region is composed mainly of a polymorphic repeat structure consisting of 3.3 kb repeat units, designated D4Z4. The number of repeat units varies from...
Facioscapulohumeral muscular dystrophy (FSHD) is a common hereditary disease of muscle. Patients with FSHD have a chromosomal rearrangement within the subtelomeric region of chromosome 4 (4q35). This region is composed mainly of a polymorphic repeat structure consisting of 3.3 kb repeat units, designated D4Z4. The number of repeat units varies from 10 to more than 100 in the population, however, in FSHD patients only 1-10 repeat units is observed because of a deletion of an integral number of these units. FSHD is caused by an epigenetic mechanism involving the contraction of a subtelomeric macrosatellite repeat, which results in marked hypomethylation of the contracted D4Z4 allele. It is likely not the structure, but the deregulation of transcription of one or more genes as a result of repeat-contraction-mediated chromatin alterations, that causes FSHD.