In addition, mutations in the receptors for B-cell activating factor (BAFF), BAFF receptor(BAFF-R) and transmembrane activator and calcium modulator and cyclophilin ligand interactor(TACI) lead to hypogammaglobulinemia (56–60) and TACI mutations are also related to sIgA deficiency (59, 60). This evidence concerns the gene TNFRSF13B and agammaglobulinemia.