SMCHD1 and facioscapulohumeral muscular dystrophy: Besides SMCHD1 and DNMT3B role in DNA methylation, telomere shortening with ageing [50], proteins of the Polycomb (inhibitors) or Trithorax (activators) family, a long non-coding RNA [51], and several antisense transcripts [22] can also affect D4Z4 epigenetics in FSHD cells and additional modifying factors are expected to be identified [43].