The Facioscapulohumeral muscular dystrophy region on 4qter and the homologous locus on 10qter evolved independently under different evolutionary pressure.

Background: The homologous 4q and 10q subtelomeric regions include two distinctive polymorphic arrays of 3.3 kb repeats, named D4Z4. An additional BlnI restriction site on the 10q-type sequence allows to distinguish the chromosomal origin of the repeats.

Variable hypomethylation of D4Z4 in facioscapulohumeral muscular dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) progressively affects the facial, shoulder, and upper arm muscles and is associated with contractions of the polymorphic D4Z4 repeat array in 4q35. Recently, we demonstrated that FSHD alleles are hypomethylated at D4Z4. To study potential relationships between D4Z4 hypomethylation and both residual repeat size and clinical severity, we compared the clinical severity score with D4Z4 methylation in unrelated FSHD patients.