Pyridox(am)ine 5′-phosphate oxidase deficiency (PNPOD; OMIM: 610090) is an autosomal recessive inborn error of metabolism caused by mutations in the gene encoding pyridox(am)ine 5′-phosphate oxidase (PNPO). The gene discussed is PNPO; the disease is hyperinsulinemic hypoglycemia, familial, 4.