The finding could one day have implications for the prevention and treatment of the disease.

"There are no immediate practical applications for patients with AMD," said study senior author Dr. Anthony Moore, a professor of ophthalmology at the Institute of Ophthalmology at the University College of London. "The aim of our research is to identify genetic factors which predispose to AMD in order to understand the causes of the problem. Improved understanding of disease mechanisms should lead in the longer term to improved treatments," he added.

"This proves that there's a genetic inherited tendency that some people have toward getting macular degeneration," said Dr. Robert Cykiert, a professor of ophthalmology at New York University School of Medicine in New York City. "What it means right now is really not that much, because there's no medication we have to treat this."

But Cykiert said he's hopeful that a simple blood test to detect the variant will emerge in the next five years and that a medication to neutralize the gene's effect will be developed within a decade.

The findings are expected to be published in the Aug. 9 issue of the New England Journal of Medicine but were to be published online Thursday.

AMD involves damage to the macula at the center of the retina. The causes of the condition are not well understood, but, in recent years, several genes have been identified that may play a role.

There are two forms of the eye disease. "Wet" AMD is caused by an overgrowth of blood vessels that creates a dead spot in the macula. "Dry" AMD, which accounts for 90 percent of all cases, causes less sight loss.

The authors of this study, based in England and Scotland, compared 847 patients with AMD with 701 unaffected people.

A variant in the complement C3 gene affected the risk of developing AMD.

Almost one-third of the population carries one copy of what's known as the "fast" variant of the gene that increases their risk of AMD by 70 percent. The 4 percent of people with two copies of the "fast" variant had more than double the risk of AMD. This "fast" variant increased the risk of both forms of the disease, the researchers found.

"A complement is a chemical that is responsible for inflammation in certain parts of the body," Cykiert explained. "Everyone has different types of complement genes, and they found that people who have the C3 complement gene have a much higher risk for AMD."

The results also provide evidence that inflammation is part of the disease process in AMD.

"It is clear from the results of this study and other recent research that inflammation plays a key role in AMD," Moore said. "The next step in the research will be to try and understand why a disturbance in the complement system, a key component of the immune system, leads to macular degeneration. We are also trying to identify other genes that are involved in AMD."

"It has been suggested that inflammation is associated with some eye diseases, and AMD in particular, and that C3 is involved in the regulation of that inflammatory process," said Warren Zimmer, a professor of systems biology and translational medicine at Texas A&M Health Science Center College of Medicine. "This is saying that inflammation may not just be associated with AMD, it's likely a causing factor. We are becoming more aware that an inflammatory process is underlying AMD. Current and future treatments could include treatments for inflammatory processes," Zimmer said.

More information

For more on age-related macular degeneration, visit the U.S. National Eye Institute.