Most common enzyme decient in urea cycle:

Urea cycle defects result from  deficiency or total absence of the activity of any of the enzymes along the pathway, particularly carbamoyl phosphate synthase I (CPSI), ornithine transcarbamylase (OTC), argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), arginase (ARG) or a deficiency of the co-factor N-acetylglutamate (NAG).   Urea cycle disorders Disorder Inheritance Enzyme defect Clinical Manifestations Hyperammonemia I Inborn defect CPS I ● Ammonia toxicity ● Ataxa ● Protein intolerance Hyperammonemia II X-linked deciency OTC ● Ammonia toxicity ● Increases levels of glutamine, ornithine and ammonia in the blood Citrullinemia Double recessive Argininosuccinate synthetase ● Increased levels of citrutlhe in the blood ● Hyperammonemia ● Mental retardation Argininosuccinic aciduria Double recessive Arginino succinate lyase ● High levels of arginino-succinate in blood, urine andCSF ● Mental retardation ● Friable tufted hair Arginemia Arginase ● Increased Arg levels in the blood, CSF and brain ● Increased levels of amino acids transported by the COAL transporter