DNMT3B and ICF syndrome: Noticeably, variants in DNMT3B (DNA methyltransferase 3 beta), known as the disease-causing gene for Immunodeficiency-Centromeric Instability-Facial anomalies (ICF) syndrome, have also been demonstrated in CVID patients [16,23], thereby linking monogenic underpinnings with epigenetic mechanisms in the pathophysiology of CVID.