Arthritis is exhibited in X‐linked CD40L deficiency, SIgAD, STAT3 GOF, Blau Syndrome, APDS, MHC I deficiency, ALPS, DGS, IPEX, WAS, XLA, ICOS deficiency, PNP deficiency, and SCID.6, 16. Here, STAT3 is linked to selective IgA deficiency disease.