The most severe form of CHI is caused by inactivating pathogenic variants in the ABCC8 (MIM 600509) and KCNJ11 (MIM 600937) genes encoding subunits SUR1 and Kir6.2 of the ATP-sensitive K(+) channel (3, 4). The gene discussed is ABCC8; the disease is congenital isolated hyperinsulinism.