citrullinemia type I

a condition caused by mutations in the ASS gene (locus: 9q34.1), which encodes argininosuccinate synthase, marked elevation in plasma and urine levels of citrulline, with hyperammonemia and sometimes secondary oroticaciduria; mild to moderate mental deficiency is a common sequela. There are two forms. The severe or neonatal form appears in the first few days of life and is characterized by severe hyperammonemia. The subacute form appears after one year of age and is marked by failure to thrive, frequent vomiting, developmental delay, and dry, brittle hair.