Heterozygous germline STAT3 loss-of-function (LOF) mutations are found in autosomal dominant hyper IgE syndrome (HIES) patients, which display immunological deficiencies with increased susceptibility to infections linked to impaired STAT3-regulated T helper 17 (Th17)-mediated immune responses and B cell function (112–116). The gene discussed is STAT3; the disease is hyper-IgE syndrome.