Genetic Cause of Form of Glaucoma Identified
2 gene variations responsible for exfoliative glaucoma, study says
THURSDAY, Aug. 9, 2007 (HealthDay News) -- Researchers in Iceland say they have identified the genetics behind a common form of glaucoma, opening the way to better diagnosis and treatment of the sight-robbing condition.
Two variants of a gene designated LOXL 1 increase the risk of what is called exfoliative glaucoma, in which clumps of a molecular fiber called elastin build up in the eye, increasing fluid pressure that gradually destroys the optic nerve, the scientists said.
"The elastin fibers are cross-linked by the LOXL 1 protein," said Dr. Kari Stefansson, a board-certified neurologist who is chief executive officer of deCODE Genetics, a biotech company based in Reykjavik, Iceland. "We have found the gene and have shown the biological plan of how a mutation can cause glaucoma."
The findings are published in the Aug. 9 issue of the journal Science.
Exfoliative glaucoma accounts for 10 percent to 20 percent of all glaucoma cases in the United States, Stefansson estimated. But the incidence varies widely among different ethnic groups and is highest among people of Scandinavian descent.
In a cooperative effort, researchers at deCODE worked with academics from the National University Hospital in Reykjavik and Uppsala University in Sweden, making a painstaking unit-by-unit study of the LOXL 1 genes in 16,000 Icelanders and Swedes, some with glaucoma, some free of the condition.
They found that two versions of the gene, each identified by a specific subunit at one location, were associated with an increased risk of exfoliative glaucoma. One variant increased the risk 26-fold, the other eightfold, compared to low-risk versions of the gene.
"This is an important advance because exfoliative glaucoma is the most common form of open-angle glaucoma with an identifiable cause," said Dr. Richard K. Lee, assistant professor of ophthalmology at the University of Miami's Bascom Palmer Eye Institute. Open-angle glaucoma accounts for more than 70 percent of all glaucoma cases.
"It is a particularly difficult form of glaucoma to treat, so it would be helpful to have a diagnostic screen to identify it early," Lee said. "The signs of exfoliative glaucoma are so subtle that they can be easily missed, so that they surgeon will not be aware of it."
The condition is notoriously more difficult to treat than other forms of glaucoma, so early diagnosis would alert the physician about the possible need for surgery, Stefansson said.
"Since we now have a marker, with one genetic test, we can see whether the increased pressure in the eye is the beginning of exfoliative glaucoma," he said. "So there would be a very low threshold to go to iridectomy," which is removal of a piece of the iris.
Stefansson said deCODE hopes to have a diagnostic genetic test on the market "before the end of this year."
Beyond early diagnosis, there's the possibility of better treatment based on the genetic finding, he said. "This is an insight that allows us to go to the nature of the genetic cause," Stefansson said. "There are future potentials when it comes to developing therapy."
A comprehensive guide to glaucoma is available from the U.S. National Library of Medicine.