HELLS and ICF syndrome: ICF syndrome patients can be classified based on the impaired gene, in addition to DNMT3B (ICF1): ZBTB24 (zinc-finger and BTB domain-containing 24, ICF2), CDCA7 (cell division cycle-associated 7, ICF3), and HELLS (helicase, lymphoid-specific, ICF4) [120,156,157].