Significance of the Urea Cycle

The main purpose of the urea cycle is to eliminate toxic ammonia from the body. About 10 to 20 g of ammonia is removed from the body of a healthy adult every day. A dysfunctional urea cycle would mean the excess amount of ammonia in the body, which can lead to hyperammonemia and related diseases. The deficiency of one or more of the key enzymes catalyzing various reactions in the urea cycle can cause disorders related to the cycle. Defects in the urea cycle can cause vomiting, coma and convulsions in newborn babies. This is often misdiagnosed as septicemia and treated with antibiotics in vain. Even 1mm of excess ammonia can cause severe and irreversible damages.

Diagnosis of Urea Cycle Defects
A blood aminogram is routinely used in the diagnosis of urea cycle disorders. The concentration of the nitrogen-carrying amino acids, glutamine and alanine, in plasma is elevated in the case of OTC deficiency. In babies, elevated levels of orotic acid in the urine may be an indicator of OTC deficiency. Increased levels of blood citrulline and argininosuccinate are also seen in cases of citrullinemia.
In older children, these disorders may present in the form of growth failure, psychomotor retardation and behavioral abnormalities. Hence, blood ammonia and urinary orotic acid monitoring and quantitation are crucial in patients with unexplained neurological symptoms.