The differential diagnoses with primary immunodeficiencies associated with immune dysregulation and subsequent autoimmune phenomena, such as CD25 deficiency, STAT5b deficiency, Omenn’s syndrome, Wiskott–Aldrich syndrome, Hyper IgE syndrome, autoimmune lymphoproliferative syndrome, autoimmune polyendocrinopathy candidiasis ectodermal dystrophy, should always be considered. The gene discussed is IL2RA; the disease is Omenn syndrome.