This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Most common genentic enzyme defect in urea cycle is 
Select and explain. 
A. Arginase, B. Arginosuccunate lyase, C. Ornithine transcarbomylase, D. Carbomoyl phosphate synthase I
A: Arginase
Answer: A: Arginase 
Explanation: OTC combines carbamyl phosphate with ornithine to make citrulline which is subsequently processed tourea (see: cycle diagram). Along with CPSI and NAGS deficiency, OTCdeficiency is the most severe of theurea cycle disorders. Patients with complete OTC deficiency rapidly develop hyperammonemia in the newborn period Ref-Harpers illustrated biochemistry 30/e p583