UCD patients (7 males and 12 females) include ornithine transcarbamylase deficiency (OTC deficiency) (14), citrullinemia type I (CTLN1) (3), hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, (HHH syndrome) (1) and argininosuccinate lyase deficiency (ASL deficiency) (1), and five of them (26%) were asymptomatic. The gene discussed is ASS1; the disease is citrullinemia type I.