Hyperprolinemia (prolinemia Type II, HPII, prolinuria) is caused by mutation in the pyrroline-5-carboxylate dehydrogenase gene (P5CDH), which encodes pyrroline-5-carboxylate dehydrogenase. This enzyme assists in the metabolism of pyrroline-5-carboxylate, converting it to the amino acid glutamine. The conversion between proline and glutamine, and the reverse reaction controlled by different enzymes, are essential factors required to maintain proper metabolism and protein production. A defect in this enyzme causes accumulation of proline in plasma; ornithine in serum; and glycine, hydroxyproline and proline in urine. Symptoms include mental retardation, acute and chronic renal failure and seizures.