Abstract
Gyrate atrophy (GA) is an inherited chorioretinal degeneration associated with hyperornithinemia. The enzyme defect is a deficiency of ornithine-δ-aminotransferase (OAT) (Valle et al Proc. Natl. Acad. Sci. 74:5159, 1977). In 4 GA patients we have noted abnormalities in the components of the labile nitrogen pool in plasma. Most impressive was a reduction in plasma ammonium concentration (GA range 0-13 μM; normal mean ± 1SD is 27±6 μM). Plasma glutamate (GA 5-22 μM; normal 43±14 μM), aspartate (GA 6-15 μM; normal 15±5 μM), and glutamine (GA 367-557 μM; normal 654±64 μM) were also reduced. Alpha-ketoglutarate was normal. No other amino acids were subnormal except lysine (owing to lysinuria). Arshiraff et al. (Clin. Res. 25:321A, 1977) reported low blood glutamates in GA and suggested that this resulted from decreased formation of glutamate in the OAT reaction. We suggest alternatively that high ornithine concentrations in GA stimulate the urea cycle, producing a new balance between the rate of urea formation and the levels of urea precursors. The rate of urea formation in GA is normal (SUN 10-17 mg/dl, urea N excretion 10 g/day). Hence urea precursors are all lowered. The corollary, that arginine (and therefore ornithine) deficiency results in hyperammonemia has been well established in animal species that require arginine. The subnormal levels of urea precursors, particularly glutamate, could play a role in retinal degeneration
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Valle, D., Brusilow, S., Walser, M. et al. 900 HYPOAMMONEMIA IN GYRATE ATROPHY OF CHOROID AND RETINA. Pediatr Res 12 (Suppl 4), 513 (1978). https://doi.org/10.1203/00006450-197804001-00905
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DOI: https://doi.org/10.1203/00006450-197804001-00905
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