In humans, more than 600 different mutations in the glucokinase gene (GCK) have been detected in patients suffering from familial, mild fasting hyperglycaemia [GCK maturity onset diabetes of the young (GCK-MODY), GCK permanent neonatal diabetes mellitus, and GCK congenital hyperinsulinism of infancy [6–11]. The gene discussed is GCK; the disease is hyperinsulinism.