Gyrate atrophy of the choroid and retina. Amino acid metabolism and correction of hyperornithinemia with an arginine-deficient diet

Four patients with gyrate atrophy of the choroid and retina were studied, all of whom exhibited the hyperornithinemia characteristic of this disorder. Elevated plasma histidine and diminished plasma lysine and branched-chain amino acids were also noted. The renal clearances of these four amino acids were not sufficiently elevated to explain their low plasma levels. In one subject, an arginine-deficient diet led to progressive reduction in plasma ornithine from 13 times normal to the upper limits of normal, along with the disappearance of ornithinuria and lysinuria. Orally administered α-aminoisobutyric acid facilitated the fall in plasma ornithine by increasing renal losses of ornithine. It also increased the clearances of most other amino acids. When plasma ornithine approached normal (<200 μM), plasma lysine became normal, plasma arginine became subnormal, and renal clearances of basic amino acids decreased. Long-term (1.5 yr) maintenance with a diet containing 10-20 g of protein plus essential amino acids served to keep plasma ornithine at between 55-355 μM; chorioretinal degeneration did not progress and vision apparently improved.