Gene therapy for blindness clears hurdle in mice

March 14, 2007

GAINESVILLE, Fla. -- University of Florida researchers have used an experimental therapy in mice to shut down a gene that plays a crucial role in a leading cause of inherited blindness.

The technique, detailed in an upcoming issue of Vision Research, involves injecting the eye with a bit of genetic material called interfering RNA, which helps disable the gene.

Normally the gene is essential for healthy eyesight, but mutated versions of it are passed from generation to generation in some families and can lead to blindness.

Disabling the gene is a step toward developing a gene therapy to treat people with retinitis pigmentosa, an inherited disease that attacks the light-sensing cells in the eye. It affects about one in 60,000 people, with an estimated 1.5 million people afflicted worldwide.

"One of the causes of the disease is mutated gene expression," said Marina Gorbatyuk, Ph.D., an assistant professor of molecular genetics and microbiology in the UF College of Medicine. "We work with rhodopsin, which is the main retinal protein. Without it, or if it is mutated, people simply won't see."

Mutated forms of the rhodopsin produce a toxic protein in the retina that kills cells that receive light. People with the disease usually notice symptoms between the ages of 10 and 30. At first they have problems seeing in dimly lit places, followed by loss of their peripheral sight. The rate of progression varies, but most patients are blind by 40.

UF Genetics Institute researchers engineered the interfering RNA into a virus, which in turn was injected below the retinas in more than a dozen normal mice. Analysis showed the technique reduced the amount of rhodopsin by about 60 percent.

With the gene drastically muzzled, scientists have begun experiments to create a therapy in which healthy versions of the gene can be introduced into the eye using an apparently harmless virus to deliver the genetic material.

"If we reduce the amount of protein formed by mutated rhodopsin, that may be sufficient to maintain vision in people who are affected by retinitis pigmentosa," Gorbatyuk said. "The second step, introducing the normal gene to the retina, will show whether we are able to restore vision in this model or not."

If both steps are perfected, scientists plan to study the treatment in a larger animal model and then possibly move to a human clinical trial.
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University of Florida

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