THE FOUNDATION FIGHTING BLINDNESS
Research Breakthrough
FROM: Bob Gray
Chief Executive Officer
The Foundation Fighting Blindness, http://www.blindness.org
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