Defects in the transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI), inducible costimulator (ICOS), B-cell-activating factor receptor (BAFF-R), and nuclear factor kappa B subunit 2 (NFKB2) genes have been identified in some patients with CVID [1, 6, 7]. The gene discussed is ICOS; the disease is common variable immunodeficiency.