Citrin deficiency (also known as citrullinemia type II) is an inherited disorder in which a protein called citrin does not work properly. This condition causes ammonia and other toxic substances to build up in the blood. One type of citrin deficiency appears shortly after birth with liver dysfunction, poor growth and low blood sugar. Symptoms are usually not severe and resolve after the first year of life; however, some infants develop chronic or fatal liver disease. Onset of the second type of citrin deficiency is usually in adolescence or adulthood and is associated with recurrent rising levels of ammonia in the blood, usually triggered by alcohol or sugar intake, certain kinds of medication or surgery. Symptoms may include behavior change, memory loss, seizure, coma, or death. For some, liver dysfunction is present as infants. Intellectual disabilities may develop in later stages or may be present in untreated individuals. Citrin deficiency may be managed by dietary treatment or liver transplantation. Long-term outcome can be excellent if appropriately managed. Citrin deficiency is caused by pathogenic variants in the SLC25A13 gene.