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Vision Special Report

Glaucoma and Your Genes

Researchers understand much about how glaucoma damages the eye, and over the past two decades they've gained a better understanding of why it happens. In a small but growing number of cases, they're finding that genetic defects are responsible for this potentially blinding disease.

Some of the first clues for a genetic basis for glaucoma came in the 1990s from Johns Hopkins researchers and others who found that people who had close relatives with glaucoma were at higher risk for developing the disease. In the landmark Baltimore Eye Survey, Hopkins researchers found that the risk of glaucoma was almost four times higher for people who had a brother or sister with it. The risk was also higher if a parent or child had glaucoma.

Yet most people with glaucoma know of no other affected family members. So, how great a role does genetics play? We don't fully know, yet. But thanks to our improved understanding of the human genome, that question may be answered sooner than later.

Genetics researchers have already identified more than half a dozen gene mutations that, if inherited, could increase the risk of developing glaucoma -- and more remain to be found. The hope is that one day, genetic tests will lead to identification of affected individuals before symptoms develop and to more effective, perhaps even personalized, treatment.

sFRP1: A Cause of Elevated IOP?
One of the main risk factors for glaucoma is elevated pressure within the eye (also known as intraocular pressure, or IOP). Normally, the trabecular meshwork, the series of filtering tubes behind the iris, allows liquids to flow in and out of the eye. However, with glaucoma, the fluids often cannot drain properly, allowing a build up of pressure in the eye. Abnormally high eye pressure over time damages the optic nerve, leading to vision loss, particularly of peripheral vision.

Researchers have discovered that a gene called sFRP1 increases IOP when it is overactive. This gene is part of a signaling pathway—the WnT-signaling pathway—that, among other functions, involves many other genes and helps keep the trabecular meshwork functioning normally. (A signaling pathway is the route that signals follow from molecule to molecule as they trigger a series of chemical reactions that control the functions of various cells.)

The researchers compared the genes expressed, or "turned on," in the eyes of people with glaucoma with those expressed in healthy eyes. They found that certain genes, including sFRP1, were turned on at a much higher rate (that is, overexpressed) in eyes with glaucoma. What's more, when they introduced the sFRP1 protein to donor eyes they found that the outflow of fluid from the eyes was reduced by 55% and IOP increased. These findings suggest that sFRP1 disturbs the WnT-signaling pathway, perhaps by binding to WnT proteins and inhibiting their activity.

Looking Ahead
In the future, researchers are likely to uncover more genes and genetic mutations associated with glaucoma, develop tests to identify them, and develop new treatments based on those findings. For now, however, the best way to screen for glaucoma is to get a complete dilated eye exam on a regular basis. And if glaucoma is detected, the best advice is to take your IOP-lowering medication as directed.

Posted in Vision on June 25, 2010

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