Patients with dominant mutations of KATP channel genes, ABCC8 and KCNJ11, may cause variable phenotype ranging from asymptomatic macrosomia, mild diazoxide responsive CHI to severe persistent hyperinsulinaemic hypoglycaemia (HH) as well as diabetes mellitus in later life (7,8,9,11). Here, KCNJ11 is linked to congenital isolated hyperinsulinism.