Homozygosity mapping and whole-exome sequencing have separately implicated four genes in ICF syndrome: DNA Methyltransferase 3B (DNMT3B, ICF type-1), Zinc-finger and BTB domain containing 24 (ZBTB24, ICF type-2), Cell division cycle associated 7 (CDCA7, ICF type-3) and Helicase, lymphoid-specific (HELLS, ICF type-4) (de Greef et al., 2011; Thijssen et al., 2015; Xu et al., 1999). This evidence concerns the gene DNMT3B and ICF syndrome.