Autosomal dominant haploinsufficiency due to heterozygous loss-of-function mutations in nuclear factor kB subunit 1 (NFKB1) causes a progressive impairment in the development of immunoglobulin-producing B cells and is now recognized as the most common monogenic cause of CVID (92, 93). This evidence concerns the gene NFKB1 and common variable immunodeficiency.