<prompt> Most common genentic enzyme defect in urea cycle isArginaseArginosuccunate lyaseOrnithine transcarbomylaseCarbomoyl phosphate synthase I  <response>: 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 30e p583 