DNMT3B and Immunodeficiency: Immunodeficiency, centromeric instability and facial anomalies (ICF) syndrome type I is a rare autosomal recessive disorder caused by mutations in DNA methyltransferase 3B (DNMT3B) (Hansen et al., 1999; Okano et al., 1999a; Xu et al., 1999; Wijmenga et al., 2000; Rigolet et al., 2007; Hagleitner et al., 2008).