Aug. 12 (HealthDay News) -- Gene therapy for an inherited form of blindness shows promise, a U.S. study shows.

The phase I trial included three patients, aged 22, 24 and 25, with a form of Leber congenital amaurosis caused by mutations in the RPE65 gene. Proper functioning of this gene is required for the production of a retina-specific form of vitamin A that's required for light-sensitive photoreceptor cells to function.

In the study, researchers injected healthy copies of the RPE65 gene under the retina in the eyes of the participants, who'd been legally blind since birth. One year after treatment, the patients could detect very dim lights that they weren't able to see prior to treatment. The results provide evidence that the newly introduced RPE65 gene is functional and is increasing the light sensitivity of the retina, according to the researchers.

The findings appear in the August online edition of Human Gene Therapy and in a letter to the editor in the Aug. 13 issue of the New England Journal of Medicine.

"At one year, we have now found that the RPE65 gene therapy appears to be safe and leads to a stable visual improvement in the patients studied. We are cautiously optimistic about these results and look forward to additional reports that address the key issues of safety and effectiveness," study author Artur V. Cideciyan, a research associate professor of ophthalmology at the University of Pennsylvania, said in a news release from the National Eye Institute.

"These results are very significant because they represent one of the first steps toward the clinical use of gene therapy for an inherited form of blindness. I anticipate that it is only a matter of time before similar techniques will be applied to other genetic diseases affecting vision," Dr. Paul A. Sieving, director of the U.S. National Eye Institute, said in the news release.

SOURCE: U.S. National Eye Institute, news release, Aug. 12, 2009