Hyperammonemia

Hyperammonemia is an abnormally high concentration of ammonia in the blood. It can disrupt brain function and arise from inherited metabolic defects or acquired disease.

Urea cycle: A series of liver reactions that converts toxic ammonia into urea for excretion. This pathway normally removes most ammonia from the body; inherited defects are a major cause of hyperammonemia.
Amino acid catabolism: The breakdown of amino acids, which releases nitrogen that must be safely eliminated. Protein breakdown supplies much of the nitrogen that becomes ammonia.
Sodium benzoate: A medication that helps remove nitrogen by promoting its excretion as hippurate. It provides an alternative route for nitrogen disposal in some hyperammonemic crises.
Ornithine transcarbamylase deficiency: An X-linked urea-cycle disorder caused by deficient ornithine transcarbamylase activity. It is a common inherited cause of severe hyperammonemia, including in newborns.
Hyperammonemia without encephalopathy: Elevated blood ammonia without clinically apparent brain dysfunction. An abnormal laboratory value does not by itself establish neurological injury.
Glutamine synthetase: An enzyme that incorporates ammonia into glutamine, especially in the brain and other tissues. Its capacity to bind ammonia can be overwhelmed when blood concentrations rise.
Liver failure: A severe loss of the liver’s ability to perform essential metabolic and synthetic functions. Damaged liver tissue may no longer clear ammonia efficiently.
Sodium phenylacetate: A nitrogen-scavenging drug that combines with glutamine to form excretable phenylacetylglutamine. It lowers nitrogen burden through a pathway that bypasses the urea cycle.
Citrullinemia type I: An autosomal recessive urea-cycle disorder caused by argininosuccinate synthetase deficiency. The blocked cycle step can produce marked ammonia accumulation.
Hepatic encephalopathy: A neuropsychiatric syndrome associated with liver dysfunction or portosystemic shunting. It overlaps with ammonia-related brain effects but is not defined by ammonia concentration alone.

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