Genes that have been associated with monogenic CVID include ICOS, NFKB1, NFKB2, IKZF1 (IKAROS), TNFSF12 (TWEAK), TNFRSF13B (TACI), TNFRSF13C (BAFF-R), CTLA4, CD19, CD81, CR2 (CD21), MS4A1 (CD20), TNFRSF7 (CD27), IL21, IL21R, LRBA, PRKCD, PLCG2, PIK3CD, PIK3R1, VAV1, RAC2, BLK, and IRF2BP2 though diseases related to these are now considered distinct clinical entities, as in the case of activated Phosphoinositide 3-kinase δ syndrome (APDS) [17,21]. The gene discussed is TNFRSF13B; the disease is common variable immunodeficiency.