SMCHD1 and facioscapulohumeral muscular dystrophy: Facioscapulohumeral muscular dystrophy (FSHD) is caused by loss of epigenetic repression in this region, either by contraction of the D4Z4 array (FSHD type 1) or by mutations in genes involved in repression maintenance, such as SMCHD1 (FSHD type 2), both of which lead to aberrant expression of DUX4 in skeletal muscle (Greef et al., 2009; Lemmers et al., 2010, 2012; Wijmenga et al., 1992).