Ornithine Loading Did Not Prevent Induced Hyper ammonemia in a Patient with Hyperornithinemia- Hyperammonemia- Homocitrullinuria Syndrome

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Abstract
Impairment of urea cycle function in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome is presumably caused, in some patients, by deficient transport of ornithine from cytoplasm into mitochondria. We studied the effect of L-ornithine on L-alanine-induced hyperammonemia in a French-Canadian proband with the syndrome by giving: (i) a 90-min intravenous alanine load (6.6 mmol/kg) together with ornithine (1.1 mmol/kg); (ii) an intravenous ornithine bolus (0.3 mmol/kg) followed by ornithine infusion (1.1 mmol/kg) 90 min prior to loading with alanine and ornithine; (iii) ornithine supplementation per os (1 g, four times daily .times. 2 wk) prior to loading with alanine and ornithine. Blood ammonia increased from high normal values to 975, 990 and 750 .mu.mol/liter (normal < 70) and urinary orotic acid from trace to 539, 494 and 1296 .mu.mol/mmol creatinine (normal 5-11) after the respective loads. Plasma alanine peaked at 1.56-4.24 mmol/liter and ornithine at 1.29-1.95 mmol/liter, but other amino acids were stable. Therefore, ornithine loading did not protect this hyperornithinemia-hyperammonemia-homocitrullinuria patient from hyperammonemia induced by amino-nitrogen loading. Renal fractional excretion of citrulline, lysine, ornithine, glycine, alanine, and tyrosine increased more than 3-fold during ornithine priming, whereas all amino acids were excreted in excess after alanine + ornithine loads; homocitrolline excretion remained unchanged; some urine collections indicated "negative reabsorption" (i.e. apparent secretion) of lysine, histidine, and citrulline. Dietary supplementation with ornithine could deplete lysine pools by impairing lysine reabsorption.

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