Study identifies new genes in patients with macular degeneration
"Macular degeneration is the leading cause of irreversible visual loss among the elderly in the United States," said Dr. Stephen Schwartz, associate professor of ophthalmology at the University of Miami's Bascom Palmer Eye Institute. "At the very least, we are moving toward a situation where we can look at the patient's DNA and give them some sort of an educated guess as to whether or not they're going to get macular degeneration when they get older."
At least that's the goal of a massive, multinational study that has uncovered seven new genes associated with age-related macular degeneration (AMD). The study is called a "genome wide association screening" (GWAS) -- a relatively new scientific technique in which the DNA from blood (or sometimes from a cheek swab) allows researchers to read thousands upon thousands of genes simultaneously.
"You don't even really have to know what you're looking for," Schwartz said. "The way the GWAS works is you take samples from people with the disease of macular degeneration and people without the disease, and you compare them across each other to see what the differences are."
As it turned out, the differences may lead to how the disease is treated in the future.
"If you think of the eye as a camera -- with the lens in the front and the film in the back -- the center of the film has a special name called the macula," Schwartz explained. "It's the center of the retina and it's really what gives you your sharpest detail vision. It's what we use to read small print or thread a needle. In a certain proportion of elderly people, the macula degenerates -- it loses function."
The disease falls into two categories: wet -- associated with bleeding inside the eye -- and dry. The former affects about 20 percent of patients, and usually kicks in any time after age 60 -- although the nationwide average is 79.
"It's really a disease that becomes more and more common the older people get," Schwartz said. "Those are the people who develop the worst visual loss. But patients with dry macular degeneration will do reasonably well, although some of them will still lose vision."
The problem -- and where the study may be beneficial -- is that it's not really known why some patients acquire AMD and other don't -- or even why some get the wet version and others the dry.
"There's reason to suspect that macular degeneration is partly genetic," Schwartz said. "But it isn't like sickle cell disease or like Tay-Sachs disease, where if you have the gene, you get the disease, and if you don't have the gene, you don't get the disease."
AMD is more likely a complex genetic disease -- meaning that it's the result of multiple genes working in combination with different environmental factors.
"People may have some of the genes that are abnormal; people may have all of the genes that are abnormal, but it still has to do with things that you eat, whether or not you smoke, what type of care you take of yourself as you get older," Schwartz said. "So genetics is a big part of the story, but not all of it. Even knowing what we do, we still don't know which are the most important genes that there are."
He hopes the GWAS will change that.
The study was the largest ever done on macular degeneration. Researchers from the University of Miami's Miller School of Medicine collaborated with an international team to examine 17,000 patients with advanced macular degeneration (either wet or dry) and 60,000 patients without. This research was conducted by the AMD gene consortium, which the NIH's National Eye Institute created in 2010 to identify the remaining genetic risk variants for AMD. It is composed of more than 60 institutions, including UM, from around the globe.
The study identified 19 different genes that seem to be associated with macular degeneration.
"Of those 19, 12 of them had been identified previously -- but seven of them were new," Schwartz said.
However, he said, that doesn't mean people should run out to get their genes tested.
"We don't know what to do with that information yet," he added. "But we're very slowly starting to put together a group of genes that -- if they're abnormal -- it increases your risk for getting macular degeneration when you get older."
Schwartz hopes that, at minimum, the results of the study will be another step toward developing a blood test that could, with some degree of accuracy, estimate one person's risk of getting macular degeneration as they age.
"It would be nice to know not only know if you're going to get macular degeneration, but if you were going to get wet or dry disease, if you were going to get it in one eye or both eyes, how bad you were going to get it," he said. "These are all things that are probably under genetic control, at least at some level. If we knew who those people were, maybe we would spend more time examining them, maybe we'd make sure they understood this, maybe we'd make sure that they went to doctors more regularly than if they didn't have these genes."
But that's the study's potential for the future. As for now, research will have to continue.
"I'm a clinician -- I'm a doctor who sees patients -- and I take care of people every day who have macular degeneration," Schwartz said. "In terms of does this change what I do in the clinic tomorrow, the answer is no, it doesn't. This is more toward advancing our scientific understanding of why some people get macular degeneration and some people don't. At the same time, it gives us ideas of places to look for new experimental treatments. These are all lines of investigation, lines of thought and study that might ultimately make for better patient care."