<prompt> Most common enzyme decient in urea cycle:ArginaseOrnithine transcarbamoylaseCarbamoyl phosphate synthase IArgininosuccinate synthetase  <response>: 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 disordersDisorderInheritanceEnzyme 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 bloodCitrullinemiaDouble recessiveArgininosuccinate synthetase Increased levels of citrutlhe in the blood Hyperammonemia Mental retardationArgininosuccinicaciduriaDoublerecessiveArginino succinate lyase High levels of arginino-succinate in blood, urine andCSF Mental retardation Friable tufted hairArginemiaArginase Increased Arg levels in the blood, CSF and brain Increased levels of amino acids transported by the COAL transporter 