Diagnosis of urea cycle disorders

Abstract

The function of the urea cycle is to remove excess ammonia from the body, ammonia being the end product of protein metabolism. Five enzymes are involved, carbamyl phosphate synthetase (CPS), ornithine transcarbamylase (OTC), argininosuccinate (ASA) synthetase, ASA lyase, and arginase. Inherited defects of all of these enzymes are known, though in the case of CPS deficiency and arginase deficiency very few cases have so far been described. These diseases are all related, since they are all defects along the pathway of ammonia detoxification, and all result in a build up of ammonia levels in body tissues and fluids. Thus they have certain clinical and biochemical features in common. The clinical features are those of ammonia intoxication coupled with protein intolerance. In general symptoms become worse after high protein intake and improve after treatment by low protein intake.