X‐linked CD40L deficiency (the most common cause of HIGM), sIgAD, STAT3 GOF, Blau Syndrome, APDS, MHC I deficiency, ALPS, DGS, IPEX, WAS, XLA, ICOS deficiency, PNP deficiency, SCID. The gene discussed is ICOS; the disease is autoimmune lymphoproliferative syndrome.