Most common enzyme deficient in urea cycle:
Explaintion: Urea cycle defects result from a deficiency or total absence of the activity of any of the enzymes along the pathway, particularly carbamoyl phosphate synthetase I (CPSI), ornithine transcarbamylase (OTC), arginosuccinate synthase (ASS), arginosuccinate lyase (ASL), arginase (ARG) or a deficiency of the co-factor N-acetylglutamate (N-GAS). Ref: Harpers illustrated Biochemistry, 28th edition Explanation: Urea cycle disorders (See the table on the next page) Urea Cycle Disorders Disorder Inheritance Enzyme defect Clinical Manifestations Hyperammonemia I Inborn defect CPS I * Ammonia toxicity * Ataxa * Protein intolerance Hyperammonemia II X-linked deficiency OTC * Ammonia toxicity * Increases levels of glutamine, ornithine and ammonia in the blood Citrullinemia Double recessive Argininosuccinate synthase * Increased levels of citrutlhe in the blood * Hyperammonemia * Mental retardation Argininosuccinic aciduria Double recessive Arginino succinate lyase * High ievels of argini no 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
Ornithine transcarbamoylase
Arginase
Carbamoyl phosphate synthase I
Arginosuccinate synthase
Urea Cycle and Disorders