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Researchers Find Gene Therapy May Halt Progression Of Macular Degeneration

Research may hold key to treating one of the leading cause of blindness in adults

The first gene therapy trial conducted at Oregon Health & Science University holds promise for treating one form of age-related macular degeneration (AMD). The multicenter phase I clinical trial revealed that injecting a gene directly into the eye to inhibit blood vessel growth was safe and well tolerated, and it may be able to halt the progression of "wet" macular degeneration. The results will be published in the February issue of Human Gene Therapy.

Wet AMD occurs when an abnormal growth of blood vessels behind the retina bleed and leak fluid, forming scar tissue that damages central vision. An estimated 1.2 million Americans suffer from this form of the disease, and that number is expected to grow as the population ages. Wet AMD, the less common though more severe form of the disease, results in more rapid vision loss than the "dry" form and is responsible for blindness in a disproportionate number of cases.

Researchers took a gene, the pigment epithelium-derived factor (PEDF) gene, and placed it in an adenovirus then injected it directly into the eye. While the virus is unable to replicate, it acts as a vehicle to incorporate the gene into the diseased eye. The gene produces PEDF protein, which inhibits formation of abnormal blood vessels.

"It is encouraging that this method of delivering therapy to the eye can be safely carried out," said Michael Klein, M.D., director of the Macular Degeneration Center at OHSU's Casey Eye Institute and co-principal investigator of the OHSU portion of the trial.

J. Timothy Stout, M.D., co-principal investigator and associate professor of ophthalmology in the OHSU School of Medicine, said, "This is an important first step, but years of research will be necessary to determine the long-term effects of this therapy and whether it will be a viable treatment for patients with AMD."

Nationwide 28 people in advanced stages of AMD enrolled in the study. The OHSU Casey Eye Institute enrolled six. They received either a single low-dose or a single high-dose of the adenovirus with the PEDF gene. After following the subjects for a year, researchers found that, on average, those who received a high dose had no growth in their macular lesions at six and 12 months post-therapy, while those that received a low dose saw some increase in their lesion size. A larger, phase II clinical trial to further evaluate efficacy is planned.

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