New pathways of nitrogen excretion in inborn errors of urea synthesis.

The defect in nitrogen excretion in patients with inborn errors of urea synthesis can be controlled by exploiting the biosynthetic pathways of readily excretable non-urea metabolites which contain nitrogen derived from ammonium, alanine, glutamate, and glutamine. Two classes of such metabolites are the urea-cycle intermediates--including citrulline, argininosuccinic acid, and arginine--and the aminoacid acylation products--hippuric acid (the glycine conjugate of benzoic acid) and phenylactylglutamine (the glutamine conjugate of phenylactic acid). Thus the urea cycle may serve as a model for the development of excretion pathways of toxic precursors which accumulate in inborn errors of metabolism.