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Gene Therapy Offers Hope for Blindness

Sept. 22, 2008 – After more than a decade of research, the first gene therapy trials in people with a rare form of blindness are under way, and experts say they are thrilled with the early findings.

The three latest patients to have the gene therapy showed dramatic improvement in light sensitivity as early as a week after treatment, researchers reported this week in the journal PNAS Early Edition.

Two other trials involving three patients each with the rare, inherited form of blindness have also been reported, and patients in those trials also showed improvements in light sensitivity and vision.

“These studies represent a triumph for gene therapy and for modern medicine, and they give hope to other patients with the same or similar blinding diseases for which there has been absolutely no treatment,” says Johns Hopkins University professor of ophthalmology Morton F. Goldberg, MD, who was not involved with the research.

Gene Therapy for Blindness

The patients in the studies had an unusual form of a rare type of inherited blindness called Leber congenital amaurosis.

Born with limited sight, people with the condition usually experience further deteriorations in vision as they grow older and they are often totally blind by the time they reach adulthood.

The condition can be caused by mutations of certain genes.

The treatment involves the injection of healthy copies of one gene, known as RPE65, into the cells of the retina in an effort to get dysfunctional cells to work better. Researchers did this by using specially engineered viruses, or vectors, to deliver the genes.

While the early studies are focusing on the safety of the gene therapy, it became clear very quickly that the treatment increased light sensitivity and improved vision, researcher Artur V. Cideciyan, MD, tells WebMD.

He characterizes the three patients in his study as “elated” with their progress.

The three patients were in their early to mid 20s when they got the treatment, which was developed by study co-author William Hauswirth, PhD, of the University of Florida in Gainesville.

“These patients, who were so courageous to volunteer for a safety study, had no expectations of improvement, but the improvement was obvious within 7 to 10 days,” Cideciyan says. “The speed of the improvement really surprised us.”

The researchers reported a 50-fold improvement in cone function, which is responsible for color and day vision, and a startling 63,000-fold improvement in rod function, which controls night vision.

But there was a catch. While night vision did improve, it took much longer for the patients to adapt to darkness than is normal. People with normal sight adjust to darkness in an hour or less, but it took eight hours or more for the patients in the study to adjust.

“This is something that we need to try and improve as we study different vector concentrations in the future,” Cideciyan says.

A patient in one of the other trials developed a small hole in the center of the retina following treatment, but the complication was believed to be the result of treatment-related surgery and not the gene therapy itself.

No major side effects were reported among the three patients in Cideciyan’s trial.

Better Blindness Treatments

About 3,000 Americans have Leber congenital amaurosis, and only about 10% of these people have the RPE65 gene mutation that would make them candidates for the genetic therapy being studied.

But similar treatments could be developed to treat other inherited retinal conditions, including some forms of macular degeneration, Goldberg notes.

“The potential is tremendous, he says.”

The results could even been more dramatic if the treatment is deemed safe enough for use in children with inherited retinal disease, says Stephen Rose, PhD, who is chief research officer for the Foundation Fighting Blindness.

“These studies together show the power of this treatment,” he tells WebMD. “We may be able to prevent blindness in children and restore functional vision in adults who have been blind for many years.”

Posted by: Dr.Health

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