After age 65, at least 1 out of 5 people develops signs of age-related macular degeneration, a condition that can block sight through the center of your eyes and cause almost total blindness, leaving only peripheral vision intact. Research has highlighted certain risk factors—having blue eyes, a family history of the disease, and smoking, for example—but no one is quite sure whether the disease is caused by something in the environment, something in the genes, or a combination of both. So three separate research teams looked at the genes of people with age-related macular degeneration to see if they could nail down a specific genetic link.

What the researchers wanted to know: Are there any genetic mutations that could cause age-related macular degeneration?

What they did: Two out of the three research teams concentrated on a chromosome that previous research had linked to age-related macular degeneration. They took blood samples from people who already had the disease or had signs they were developing it, as well as healthy volunteers. Isolating the chromosome from blood cells, they then examined its genes to see if there were variations between the diseased and healthy groups. In the third study, the researchers also looked for genetic variations between diseased and healthy people, but they examined the entire genome rather than concentrating on one chromosome.

What they found: All three teams found a genetic variation in the complement factor H gene. The gene helps the body attack invading pathogens and spare healthy cells, hinting that age-related macular degeneration might be at least partially caused by a malfunction that leads to an attack on healthy cells. The researchers say that one particular variant can increase a person's risk of developing the ailment by as much sevenfold. Having the variant does not guarantee that a person will develop the disease—some people without the disease have it and, on the flip side, some people with the disease do not. However, the variation is much more common in those with the disease.

What it means to you: For patients, these studies don't yet have much relevance, but they do help researchers develop treatments for the disease. If, as it seems from the genetic variation, the disease is related to the immune system, future research can investigate ways to treat the disease through drugs that regulate that system. This research also shows that genetic factors may play a big role in the development of the disease, but, because the genetic variation was present without the disease, environment also likely plays a role.

Caveats: All of the studies were done on white people with similar backgrounds, so that the genomes of each person would vary as little as possible. The research might not apply to other populations.

Find out more: USNews.com has covered previous research on this topic.

In addition, the Macular Degeneration Partnership has information about the disease in large type, including how the disease develops and how to prevent it.

Read the articles: Klein, R.J. et al. "Complement Factor H Polymorphism in Age-Related Macular Degeneration." Science. Published online March 10, 2005.

Edwards, A.O. et al. "Complement Factor H Polymorphism in Age-Related Macular Degeneration." Science. Published online March 10, 2005.

Haines, J.L. et al. "Complement Factor H Variant Increases the Risk of Age-Related Macular Degeneration." Science. Published online March 10, 2005.

Abstracts online:

Haines et al: www.sciencemag.org/cgi/content/abstract/1110359v1

Edwards et al: www.sciencemag.org/cgi/content/abstract/1110189v1

Klein et al: www.sciencemag.org/cgi/content/abstract/1109557v1