GCK and congenital isolated hyperinsulinism: Most cases of CHI are “channelopathies” caused by mutations in the β-cell KATP channel genes ABCC8 and KCNJ11. Some CHI cases can be classified as “metabolopathies” because there is an underlying defect in metabolic enzymes such as glucokinase and glutamate dehydrogenase (GDH) (2).