HNF4A and congenital isolated hyperinsulinism: Dominant forms of CHI are due to either activating mutations in mitochondrial matrix enzymes, GLUD1 (glutamate dehydrogenase 1) and UCP2 (mitochondrial uncoupling protein 2), or to mutations in HNF4A (hepatocyte nuclear factor 4 alpha) and SLC16A1 (monocarboxylate transporter 1).