Citrullinaemia (argininosuccinic acid synthetase deficiency) and Argininosuccinic aciduria (argininosuccinate lyase deficiency) are urea cycle disorders. They are both caused by a missing enzyme from a process inside cells called the urea cycle. Infants with these disorders are not able to convert ammonia into urea. Ammonia builds-up in the body and is toxic to the brain. Ammonia is a waste-product and is normally produced during the breakdown of protein from food or muscle.
The gene defect for these disorders is inherited when both parents have the same abnormal gene and unknowingly pass it on to their baby. A parent who has the abnormal gene, but not the disease, is called a carrier. The health of a carrier is rarely affected. However, for each pregnancy of two such carriers, there is a 1 in 4 chance that the child will be born with the disease. Both these disorders occur in about 1 in every 100,000 births in Australia.
Both disorders usually cause toxic levels of blood ammonia in the first days of life. This can lead to vomiting, lethargy, seizures, coma and death. There are also some less severe forms, which can cause intellectual impairment and may go undetected for months or years.
Dialysis is sometimes needed to lower the blood ammonia. The blood ammonia is then kept down with a low-protein diet and medications that include arginine and sodium benzoate and/or sodium phenylacetate.
Both these disorders are detected by increased levels of citrulline in the blood.