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Gene Therapy Shows Promise for Curing Day Blindness

A new advance in gene therapy is providing hope for people with a debilitating retinal disease known as achromatopsia or day blindness. Foundation-funded researchers from the University of Pennsylvania have used gene therapy to successfully treat dogs with the same condition.

Thanks to the success of this study, Applied Genetic Technologies Corporation (AGTC), a gene therapy development company and partner of the Foundation, has begun FDA-regulated preclinical testing to support the launch of a human study of the treatment.

The canine study’s lead investigators, Andras Komaromy, D.V.M., Ph.D., and Gustavo Aguirre, V.M.D., Ph.D., reported their results in the journal Human Molecular Genetics (online, April 21, 2010).

Achromatopsia only affects cones — the photoreceptors that enable people to see during the day or in well-lit environments. Cones also provide central vision and the ability to see colors and details. Hence, people with achromatopsia also have reduced visual acuity and difficulty seeing colors. The disease is non-progressive in humans; it does not get worse over time. At night and in dark settings, people with achromatopsia see normally (the same as unaffected people see in the dark).

Drs. Komaromy and Aguirre believe that cones of people with achromatopsia survive, despite the genetic variation that causes them to function improperly, resulting in day blindness. By delivering a normal gene to the cones, the investigators hope to correct the day blindness and other visual impairments.

The gene therapy implemented in the achromatopsia canine study uses a delivery mechanism — a man-made therapeutic virus known as an adeno-associated vector or AAV — that comes from the same family of viruses that are being used in the Foundation-funded clinical trial of gene therapy for Leber congenital amaurosis (LCA) at the Children’s Hospital of Philadelphia. AAVs are also being used at the LCA clinical study at Moorfields Eye Hospital in the U.K., the LCA clinical study at the Universities of Pennsylvania and Florida, and an LCA clinical trial at AGTC. In these four studies, 27 children and young adults who were nearly blind had varying levels of vision restored.

Dr. Aguirre used an AAV in the earlier, preclinical study of LCA gene therapy that gave vision to more than 60 Briard dogs born blind — including the world-famous Lancelot.

Dr. Aguirre notes that the success in the achromatopsia and LCA studies would not have been possible without strong collaborations with other investigators. For example, William Hauswirth, Ph.D., University of Florida, led gene therapy development efforts for both treatments, and Samuel Jacobson, M.D., Ph.D., University of Pennsylvania, has played key clinical roles in advancing both therapies.

Stephen Rose, Ph.D., chief research officer, Foundation Fighting Blindness, says that these studies are opening the door for using gene therapy to treat a variety of retinal conditions. “There is a lot of momentum for using gene therapy to treat a wide range of retinal diseases including Stargardt disease, Usher syndrome, and retinitis pigmentosa,” he says. “More clinical trials of gene therapy are likely to begin very soon.”

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