Three patients, who received gene therapy for an inherited form of blindness, continued having vision improvements even after a year, a new study has revealed.
This is the first study to report one-year gene therapy safety and efficacy results in treating young adults with Leber Congenital Amaurosis (LCA), a hereditary condition that causes severe vision impairment in infants and children.
Previously, such improvement in vision after was observed within weeks of undergoing gene therapy.
The three patients - 22, 24 and 25 years old - who received the gene therapy have a specific type of LCA caused by a genetic mutation in the RPE65 gene.
The gene normally makes a critical protein in the visual cycle. Without this RPE65 protein, light-sensitive photoreceptor cells are starved of a retina-specific form of vitamin A and cannot function, blocking vision.
For correcting this genetic defect, researchers targeted retinal regions with impaired, but intact, photoreceptors and injected healthy copies of the RPE65 gene under the retina.
One year after the single injection, the healthy genes continue to make this critical protein, increasing the retina's sensitivity to light.
"We had previously shown that RPE65 gene therapy can completely reverse one of the two components of this complex disease and provide patients with increased day- and night-vision within weeks. We now show that the longevity of the visual improvements extends to at least one year," said Dr. Artur V. Cideciyan, Research Associate Professor of Ophthalmology at the University of Pennsylvania School of Medicine and lead author of the publications.
One patient was able to read an illuminated clock for the first time, and the new ability was not caused by a further increase in light sensitivity, which remained unchanged from 1 to 12 months after the treatment.
But the visual improvement was caused by a slow change in the direction of focus to her treated retina. The change appeared 12 months after gene therapy, but not before.
The findings are published in Human Gene Therapy, now online, and in the New England Journal of Medicine (NEJM).