A mutation in interferon regulatory factor-2 binding protein 2 (IRF2BP2), inducible T-cell costimulatory (ICOS) deficiency, suppressor of cytokine signalling 1 (SOCS1), protein tyrosine phosphatase non-receptor type 2 (PTPN2) and cytotoxic T lymphocyte antigen 4 (CTLA4) were seen in one patient each. The gene discussed is SOCS1; the disease is hyperinsulinemic hypoglycemia, familial, 4.