Hyperammonemia in Lysinuric Protein Intolerance

Two brothers with hyperdibasicaminoaciduria and postprandial hyperammonemia showed characteristics of lysinuric protein intolerance. Intravenous alanine load produced hyperammonemia that was aborted by oral supplementation with arginine in one brother but not in the other, although both patients had almost the same intestinal malabsorption of arginine. This occurrence suggests that even a small amount of arginine, when absorbed into the blood, can normalize the affected ammonia metabolism of lysinuric protein intolerance. Two patients with cystinuria developed marked hyperammonemia when they received an intravenous alanine load after a 19-hour fast. As both patients displayed a reduced plasma concentration of arginine and ornithine at this time, the hyperammonemia was assumed to arise from the low plasma amino acid level. It seems likely that a decrease in plasma levels of urea cycle substrate causes a failure of the tissue urea cycle metabolism. Thus the impaired ammonia metabolism in lysinuric protein intolerance would be attributed to the low plasma arginine and ornithine levels.