GCK and congenital isolated hyperinsulinism: Rarer forms of CHI have been described as caused by defects in HADH (encoding short-chain L-3-hydroxyacyl-CoA dehydrogenase), GLUD1 (encoding glutamate dehydrogenase), GCK (encoding glucokinase), HNF4A (encoding hepatocyte nuclear factor 4α), HNF1A (encoding hepatocyte nuclear factor 1α), SLC16A1 (encoding monocarboxylate transporter, MCT1), UCP2 (encoding mitochondrial uncoupling protein 2), HK1 (hexokinase 1), PGM1 (phosphoglucomutase 1), and CACNA1D (l-type calcium channel α-subunit) (1–7, , , , , , ).