SMCHD1 and facioscapulohumeral muscular dystrophy: In 5% of cases, FSHD is caused by digenic inheritance of a permissive 4qA allele (8-20 D4Z4 units) and a genetic variant in an epigenetic repressor of the D4Z4 repeat array (FSHD2), mostly in structural maintenance of chromosomes flexible hinge domain-containing 1 (SMCHD1) [13], a chromatin modifier involved in different processes including the maintenance of DNA methylation and X chromosome inactivation [14, 15].