We also know that knocking out Arg1 was lethal in mice due to hyperammonemia caused by arginase deficiency, whereas the Arg2 knockout mice had intact phenotypes and Arg1/Arg2 double knockout mice exhibited the same arginase deficiency phenotype as the Arg1 single knockout mice (47, 48). The gene discussed is ARG2; the disease is hyperinsulinemic hypoglycemia, familial, 4.