NFKB1 and common variable immunodeficiency: So far, several single-gene defects such as ICOS, CD19, CD20, CD21, CD27, CD81, IL21, IL21R, LRBA, PRKCD, RAC2, TNFSF12, CTLA4, PLCG2, NFKB1, NFKB2, PIK3CD, PIK3R1, VAV1, BLK, IKZF1, IRF2BP2, as well as mutations in TNFRSF13B and TNFRSF13C have been identified in CVID (1, 2, 5, 6).