August 31, 2009

Gene Therapy Shows Promise for Eye Condition

Photo of a retina Retinal photo of a patient with Leber congenital amaurosis (LCA). NEI

Three young adults who received gene therapy for a blinding eye condition remained healthy and maintained visual gains one year later, researchers reported. One patient also noticed a visual improvement that helped her perform daily tasks.

Leber congenital amaurosis (LCA) is a currently untreatable hereditary condition that causes severe vision loss and blindness in infants and children. The 3 patients in the study—aged 22, 24 and 25—have been legally blind since birth due to a specific form of LCA caused by mutations in the RPE65 gene. The protein coded by this gene is needed for the production of a retina-specific form of vitamin A that allows light-sensitive photoreceptor cells to function.

The RPE65 form of LCA offers an opportunity for treatment because it leaves some photoreceptors intact. Researchers at the University of Pennsylvania and the University of Florida pinpointed an area of intact photoreceptors in the retina of each patient. They then injected healthy copies of the RPE65 gene under the retina in this area. The ongoing phase I clinical trial is supported by NIH's National Eye Institute (NEI).

Three independent groups previously reported the short-term benefits of this procedure. In a paper published online on August 3, 2009, in Human Gene Therapy, the researchers noted that, one year after the procedure, the therapy had not provoked a detectable immune response, a risk in gene therapy procedures. The patients' ability to read letters on an eye chart remained unchanged, but all 3 patients could detect dim lights that they weren't able to see before treatment. This provides evidence that the newly introduced RPE65 gene is functional and is increasing the light sensitivity of the retina.

The scientists also reported in the August 13, 2009, issue of the New England Journal of Medicine that, at 12 months, one patient noticed that she could read an illuminated clock on the dashboard of a car for the first time in her life. When the researchers performed additional tests, they found that, rather than focusing on objects using the region of the retina where the sharpest central vision normally occurs, this patient had gradually begun to use the area of the retina that had been treated with gene therapy.

“This interesting finding shows that over time, a person visually adapted to gene therapy in a meaningful way,” says principal investigator Dr. Samuel G. Jacobson of the University of Pennsylvania. “As we continue our studies, we will look more closely at whether these slow visual gains could be accelerated with visual training.”

The researchers will continue to follow these patients over the next several years to monitor safety and to learn whether the visual benefits remain. The ongoing trial also includes additional groups of LCA patients—children as well as adults—who are receiving different doses of the RPE65 gene therapy.

“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,” says NEI Director Dr. Paul A. Sieving. “I anticipate that it is only a matter of time before similar techniques will be applied to other genetic diseases affecting vision.”

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