The finding of generalised hyperpigmentation of the remaining RPE helps to clinically distinguish gyrate atrophy from choroideremia. In the early stages, patients have large, geographic peripheral paving-stone–like areas of atrophy of the RPE and choriocapillaris, which gradually coalesce to form a characteristic scalloped border at the junction of normal and abnormal RPE..
Affected patients usually develop night blindness during the first decade of life and experience progressive loss of visual field and visual acuity later in the disease course. The clinical diagnosis can be confirmed by measuring serum or plasma ornithine levels; molecular confirmation can be obtained by mutational analysis of the OATgene. Occasionally, older patients present with an uncommon syndrome of peripheral chorioretinal atrophy that closely mimics gyrate atrophy; normal plasma ornithine levels in such patients exclude the diagnosis.
What treatments are available?
Although dietary restriction of arginine has been used to treat some gyrate atrophy patients, the diet is very difficult to maintain and must be monitored by paediatricians with experience in metabolic disease. Vitamin B6 treatment lowers the plasma ornithine levels in a small percentage of gyrate atrophy patients.
Whether such a reduction improves the long-term visual outcome is unknown, but, unlike arginine restriction, vitamin supplementation is relatively easy to administer. Long-term vitamin therapy should be considered only for patients whose ornithine levels can be shown to drop in response to treatment.