In humans, loss-of-function mutations of NF-κB1 represent the most common NF-κB subunit deficiency; the affected individuals present with common variable immunodeficiency (CVID) which leads to a somewhat milder immunodeficiency phenotype compared to the CID observed for c-REL deficiency, and is mostly accompanied by a reduction in isotype switched memory B cells [65,66,67]. This evidence concerns the gene REL and common variable immunodeficiency.