Notably, although the number of D4Z4 repeats seems to be a critical determinant of the age of onset and clinical severity of FSHD, patients without D4Z4 contraction (phenotypic FSHD or FSHD2) as well as healthy individuals with D4Z4 contraction (carrier) have been also identified [4], [5]. This evidence concerns the gene SMCHD1 and facioscapulohumeral muscular dystrophy.