The immunodeficiency, centromeric instability, facial anomalies syndrome, type 1 (ICF1) can be caused by mutations in DNMT3B. The impaired function of this gene leads to changed methylation of regulatory regions of lineage-specific immune-related genes during development which cause the phenotype of ICF1. The gene discussed is DNMT3B; the disease is immunodeficiency-centromeric instability-facial anomalies syndrome 1.