A form of diazoxide-sensitive diffuse hyperinsulinism caused by a lowered threshold for insulin release. Characterised by excessive/uncontrolled insulin secretion and recurrent episodes of profound hypoglycaemia induced by fasting and protein rich meals, requiring rapid and intensive treatment to prevent neurological sequelae. Activating mutations of GCK (7p15.3-p15.1) that encodes glucokinase have been identified as the cause.