Immunodeficiency, Centromere instability, and Facial anomalies (ICF) syndrome which is caused by mutations in DNMT3b [166], is characterized by centromeric instability of chromosomes 1, 9 and 16, which is associated with abnormal hypomethylation of CpG sites within pericentromeric satellite regions. The gene discussed is DNMT3B; the disease is immune system disorder.