Gyrate atrophy of the choroid and retina. Biochemical considerations and experience with an arginine-restricted diet.

Ornithine-delta-aminotransferase deficiency is the primary biochemical defect in gyrate atrophy of the choroid and retina and results in the characteristic accumulation of ornithine. An additional consequence of this inborn error is that arginine, the precursor of ornithine, becomes an essential amino acid. Therefore, to reduce the accumulated ornithine, we placed nine gyrate atrophy patients on an arginine-restricted diet. Plasma ornithine decreased by 50 to 85% within one month. Orally administered, alpha-aminoisobutyric acid facilitated the reduction in ornithine by augmenting renal losses. Over the long term, three patients have maintained near normal plasma ornithine concentrations from 4 to 32 months. Two patients have maintained less striking reductions in ornithine, and four have either been poorly controlled or have terminated the diet. Urinary losses of arginine and ornithine in gyrate atrophy patients with high or low plasma ornithine concentrations are less than 50% of the estimated arginine intake. This observation suggests that the bulk of ingested arginine is somehow metabolized despite the severe reduction in ornithine-delta-aminotransferase activity.