STAT5B deficiency (MIM 245590), a rare cause of GHIS with immunodeficiency, is an AR disorder, first described in a patient with severe short stature (height SDS −7.5), who was T-lymphopenic10, 11 and succumbed to a progressive pulmonary disease12. The gene discussed is STAT5B; the disease is hyperinsulinemic hypoglycemia, familial, 4.