Citrullinemia is a rare life-threatening disorder that manifests as a damaged urea cycle that allows ammonia and other toxins to build up in the blood and cerebrospinal fluid. There are two subtypes: type 1 is caused by mutations in the ASS1 gene and type 2 is caused by mutations in SLC25A13 gene. Type 1 ("classic") is more common. It can present in infancy as the toxins accumulate with symptoms such as lethargy, failure to thrive, vomiting, hepatomegaly, syncope, and seizures. Type 2 occurs mostly within the Japanese population and manifests within the nervous system, causing symptoms such as confusion, lethargy, drowsiness, seizures, and coma. Some patients will have developmental and physical delays. It can appear from late childhood to old age.

A milder form of type 1 citrullinemia may present in later childhood or adulthood and is characterized by migraines, vision impairment, lethargy, and balance disorders. Type 1 can also be completely asymptomatic.

Treatments vary to support the individual presentation.