Leukocyte urea cycle enzymes in hyperammonemia.

All enzymes of the urea cycle are demonstrable in circulating leukocytes. They show the same relative activities as those in liver except for argininosuccinate synthetase + lyase (combined) which seems to be disproportionately active. To see whether leukocytes reflect liver activity, blood from patients with three hepatic urea cycle disorders was tested. In each case, the leukocytes showed the same enzyme deficiency as was apparent from a liver biopsy (Table 4). Leukocyte assays appear to be reliable indicators of the enzyme lesions in inherited urea cycle enzyme defects and therefore may obviate the need for liver biopsy.