While the specific role of DNMT3B variants in FSHD development is not fully clear, the described mutations have been shown to either disrupt the C2C2-type zinc-finger motif in ATRX-DNMT3-DNMT3L domain in exon 15 or reside in the C-terminal catalytic domain of DNMT3B in exon 19 and possibly alter its DNA methylation activity. The gene discussed is ATRX; the disease is facioscapulohumeral muscular dystrophy.