<prompt> Citrullinemia type I results from deficiency of theIsocitrate dehydrogenaseArgininosuccinate synthasePyruvate dehydrogenaseSucinyl Co-A synthase  <response>: B Argininosuccinate synthase Citrullinemia type I CTLN1 presents as a clinical spectrum that includes an acute neonatal form the classic form, a milder late-onset form, a form without symptoms or hyperammonemia, and a form in which women have onset of severe symptoms during pregnancy or post partum. Citrullinemia type I results from deficiency of the enzyme argininosuccinate synthase ASS, the third step in the urea cycle in which citrulline is condensed with aspartate to form argininosuccinic acid. Untreated individuals with the severe form of citrullinemia type I have hyperammonemia plasma ammonia concentration 1000- 3000 pmolL. Plasma quantitative amino acid analysis shows absence of argininosuccinic acid and concentration of citrulline usually greater than 1000 pmolL normal: 50 pmolL. Argininosuccinate synthase enzyme activity, measured in fibroblasts, liver, and in all tissues in which ASS is expressed, is decreased. ASS1 is the only gene in which mutation is known to cause citrullinemia type I. 