In the case of DNMT3B, homozygous loss-of-function mutations cause Immunodeficiency Centromeric instability and Facial anomalies syndrome type 1 (ICF1) [23] which displays chromosome instability and hypomethylation of constitutive heterochromatin [62,63]. This evidence concerns the gene DNMT3B and immunodeficiency-centromeric instability-facial anomalies syndrome 1.