DNMT3B and immunodeficiency-centromeric instability-facial anomalies syndrome 1: According to the molecular genetic evidence, ICF can be divided into five subtypes: about 60% of patients carry DNMT3B variants, known as ICF syndrome 1 (ICF1, OMIM 242860); nearly 30% of ICF individuals belong to ICF syndrome 2 (ICF2, OMIM 614069), caused by variants in ZBTB24; ICF syndrome 3 (ICF3, OMIM 616910) and ICF syndrome 4 (ICF4, OMIM 616911) are respectively associated with variants in CDCA7 and HELLS; Only very few cases of ICF with unknown causative genes are classified as ICF syndrome X (ICFX) (1, 5).