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Risk factor. Immunofluorescence shows the presence of complement factor H (green) in the human retina.

Eye-Opening Gene

Three independent teams have pinpointed a gene linked to age-related macular degeneration, the leading cause of sight loss in the elderly. The studies, published online by Science on 10 March, give researchers a specific molecular target for the largely untreatable disease, which clouds the central part of the retina.

The researchers discovered that the disease is linked to mutations in a gene for an immune system protein called complement factor H. One team, led by Yale University mathematician Josephine Hoh, reports that a single copy of the allele raises the risk to 4.6-fold. People with two copies of the allele face a risk of macular degeneration 7.4 times higher than normal.

Researchers have suspected for decades that macular degeneration runs in families. By using traditional techniques called family gene linkages to zoom in on smaller and smaller segments of chromosome 1, teams at the University of Texas and Vanderbilt University eventually found the gene for complement factor H, a protein that plays a key role in the body's inflammatory response. As they completed this painstaking work, Hoh's team used a relatively new technique, a so-called whole-genome scan of single-nucleotide polymorphisms, or SNPs, to nail the gene. "The idea that the immune system plays a role in macular degeneration has been around a long time," says Hemin Chin, director of the ocular genetics program at the National Eye Institute in Bethesda, Maryland, who did not participate directly in the study. In particular, white spots behind the retina called drusen--which cloud and eventually block central vision--were known to attract immune proteins.

It's not known how many cases of macular degeneration are caused by genetic variation, Hoh says, and the study is only the first step in unraveling a complex, multigenic disease. "We're now going to study other populations to gauge the worldwide prevalence" of the SNPs linked to increased risk, she says. "It's exciting to see the human genome data pay off with such a common disease."

Related sites
Josephine Hoh's home page
More about macular degeneration, from the National Eye Institute