Urea Cycle Defects

Urea cycle enzymes are six enzymes all located in the liver &. An inherited defect of one of these enzymes causes neonatal syndrome frequently characterized by hyperammonemia and severe central nervous system damage. In some cases of urea cycle disorders, medical treatment based on dietary protein restriction and other measures aimed at increasing ammonia excretion is effective in the short term amelioration of the disease. However, in the long term patients with urea cycle defects are at high risk of protein deficiency, growth retardation liver failure $ and recurrence of coma.
The most common defect of the urea cycle is the deficiency of ornithine carbamoyltransferase (OTC), an X-linked dominant disease. This disease may be fatal in the neonatal period for the severe central nervous system damage due to hyperammoniemia. The diagnosis is made by finding very high serum ammonia levels and severe oroticaciduria.
Liver transplantation can be lifesaving in these patients, if it is performed before irreversible central nervous system damage occurs. Three urea cycle defects have been successfully treated by liver transplantation: OTD deficiency, carbamoyl phosphate synthetase deficiency and argininosuccinate synthetase deficiency.