Research Breakthrough

FROM: Bob Gray
Chief Executive Officer
The Foundation Fighting Blindness,

Media Alert:

We wanted to alert you to an important breakthrough study for retinal degeneration that will be carried by the Associated Press wire service when the press embargo lifts at 5 p.m. on Monday, September 27. AP wire stories are often carried in newspapers across the country, so you may receive calls about the study. The article below gives an overview of the study.

Breakthrough for Gene-based Pharmaceutical Therapies

By Tom Hoglund

In a landmark study, published in the October issue of Nature Medicine, researchers from France substantially slowed vision loss in an animal model of retinitis pigmentosa (RP) using a commonly prescribed heart medication called diltiazem. This study represents the first time vision researchers have successfully used gene-based pharmaceutical therapy to slow the course of retinal degeneration. Gene-based pharmaceutical therapy exploits the knowledge gained from studying how a mutant gene causes cellular dysfunction and vision loss. With this knowledge, researchers can test drugs that overcome the disease process.

Commenting on this major breakthrough, Dr. Gerald Chader, Chief Scientific Officer of The Foundation Fighting Blindness, stated, "To develop the most effective treatments, we must first understand how a healthy gene normally functions in retinal cells and how a genetic mutation leads to vision loss. Thanks to a decade of concentrated genetic research, we now know many of the mutant genes that cause retinal degeneration. Foundation researchers are now working to create similar breakthroughs for other forms of retinal degenerative disease. This study validates The Foundation's investment in genetic research."

In this particular study, researchers used an animal model called the rd mouse. The rd mouse exhibits an autosomal recessive form of RP that is also found in humans. In previous studies, Foundation researchers found that this form of RP results from a mutation in a gene called PDE beta. This gene produces a protein that is part of an enzyme called phosphodiestrase (PDE). PDE is a light-sensitive enzyme that helps regulate calcium channels in the outer membrane of photoreceptor cells. Mutations in the PDE beta gene are thought to interfere with the function of these calcium channels, which leads to photoreceptor cell degeneration and vision loss.

In this study, the French scientists found that the drug diltiazem, a calcium-channel blocker known under the brand name Cardizem, partially overcame the gene defect to preserve visual function in the rd mouse. The number of functioning rod photoreceptor cells was 248 percent higher in treated mice than in the control mice who did not receive diltiazem.

These results suggest that people with mutations in the PDE beta gene and possibly other mutant genes involved in the regulation of calcium transport may benefit from calcium- channel blockers such as diltiazem. However, it must be stressed that these findings are preliminary. The dosages used in the study were much higher than are commonly used for heart conditions. Furthermore, calcium channel blockers have not been tested in children and so their safety is not yet known. Clinical trials are needed to gauge the efficacy of the drug in humans and to establish a safe and effective drug dosage. Nonetheless, this study offers the first exciting glimpse of a future filled with effective, sight-saving drugs.

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Date last modified September 27, 1999