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]. This evidence concerns the gene TNFRSF13B and activated PI3K-delta syndrome.