Gain-of-function mutations of STAT3 cause early-onset lymphoproliferative disease and autoimmunity [16], those of STAT1 lead to chronic mucocutaneous candidiasis, but also autoimmunity [17], and dominant negative mutations of STAT3 cause a hyper-IgE syndrome, known as Job syndrome [18]. Here, STAT3 is linked to hyper-IgE syndrome.