Such diseases include CD25 or IL-2RA deficiency, mutations within STAT5b, STAT1 or STAT3, Dedicator of Cytokinesis 8 (DOCK8) deficiency as well as infantile or eosinophilic enteropathies and severe combined immunodeficiency (SCID) (Figure 6). The gene discussed is IL2RA; the disease is severe combined immunodeficiency.