TUESDAY, July 18, 2006 (HealthDay News) -- A specific gene variant has a major impact on the risk for age-related macular degeneration (AMD), the leading cause of vision loss in the elderly, Dutch researchers report.
The gene governs production of a molecule called complement factor H (CFH), which is involved in inflammation. Persons with two copies of a variant of the gene were at 11 times the risk of developing AMD compared to non-carriers, according to a report in the July 19 issue of the Journal of the American Medical Association.
More than a third of individuals in the study carried the higher-risk gene, the researchers found.
The relationship between the CFH gene variant and AMD has been established by a number of smaller studies, said Lindsay A. Farrer, chief of the genetics program at Boston University, who helped conduct one of those studies.
"The most important contribution here is that this may be the first report of this association in a community sample, as opposed to prior reports based on small clinical samples," Farrer said.
Physicians at Erasmus Medical Center in Rotterdam followed 5,681 residents of that city who were 55 years or older when the study began in 1990.
Those who carried the gene variant had a 48 percent risk of developing AMD by age 95, compared to a 22 percent risk for non-carriers, the researchers found.
The study also assessed other risk factors, such as smoking and blood levels of C-reactive protein, a marker of inflammation. It found that smoking increased the risk of AMD 34-fold for carriers of the gene variant, while high C-reactive protein levels increased their risk 28-fold.
"There was an interactive effect between smoking and this gene," Farrer said. "The effect appears more than additive, so there is some interaction going on."
But another expert said there is a broader range of risk factors for AMD, which involves a degradation of the central part of the retina.
"The condition is likely polygenic [involving several genes]," said Neal Adams, chief of the Wilmer Eye Institute division of visual physiology at Johns Hopkins Hospital in Baltimore. "These genes either act alone or in combination with environmental factors. We are trying to understand how many genes are involved."
The study results bring scientists closer to understanding the genetic and molecular mechanisms involved so they can devise targeted treatments for AMD, Adams said. "We can target either the genetic defect or the pathway that results from the genetic effect," he said.
What is still needed is a study that looks at all the possible risk factors for AMD, including dietary elements such as cholesterol, said Dr. Richard Spaide, a retina specialist at the Manhattan Eye, Ear and Throat Hospital in New York City.
"This is getting a little closer to it," Spaide said of the Rotterdam study. "But so far no one big study has looked at everything, including smoking, family history, diet and overweight."
AMD is a growing medical issue in the United States. Researchers have estimated that a third of Americans will develop some form of the condition by age 75. Ophthalmologists currently often have no treatment to offer an aging individual as his or her central vision loses its sharpness.
Since many people are unknowing carriers of the gene variant -- 36.2 percent of those in the Rotterdam study had it -- preventive measures should be stressed, Spaide said.
"You can't do anything about age, but you can do something about diet and smoking," Spaide said.
Learn more about age-related macular degeneration from the U.S. National Eye Institute.