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. The gene discussed is STAT3; the disease is purine nucleoside phosphorylase deficiency.