An international group of investigators has identified seven new genetic regions associated with age-related macular degeneration (AMD), a common cause of blindness in older individuals. The findings, reported online March 3 in Nature Genetics, could point to new biological pathways and therapeutic targets for AMD.
The AMD Gene Consortium, a network of 18 research groups supported by the National Eye Institute, also confirmed 12 genetic loci identified in previous studies. The study represents the most comprehensive genome-wide analysis of genetic variations associated with AMD.
The consortium's efforts have now explained up to 65 percent of the genetics of AMD, said Jonathan Haines, Ph.D., director of the Vanderbilt Center for Human Genetics Research.
In addition to genetic causes, which may account for about half of all cases of AMD, risk factors include age, smoking, high blood pressure, obesity and diet.
"We're getting closer and closer to understanding the full list of risk factors for AMD," said Haines, one of the lead authors of the study and principal investigator of the coordinating center for the consortium.
AMD is a progressive neurodegenerative disease that kills photoreceptor cells in the macula -- the region of the retina responsible for sharp, detailed central vision. As AMD advances, it robs individuals of the central vision necessary for everyday activities like reading, driving, watching television and identifying faces. About 2 million people in the United States have advanced AMD, according to the National Eye Institute.
Haines and others discovered the first genetic risk factor for AMD in 2005 -- a gene called Complement Factor H, which is involved in inflammatory signaling pathways. Since then, researchers have identified a number of other genetic loci associated with AMD, but the studies usually involved small numbers of individuals.
"It was very clear that if we wanted to make real progress in understanding the genetics of AMD, we needed to pull all of these various datasets together -- which is what the AMD Gene Consortium has done," Haines said.
A strength of the AMD Gene Consortium, Haines noted, is the participation of groups from all over the world. The consortium combined existing genome-wide association scans (GWAS) and performed additional genotyping studies. The researchers examined genetic data from more than 17,000 patients with advanced AMD and more than 60,000 people without AMD.
The loci they identified include genes involved in immune system signaling, lipid metabolism, remodeling of the matrix that surrounds cells and blood vessel development. The researchers are continuing to study the genetic regions, Haines said.
"This paper is a global population look at genetic loci, and now we're drilling down to the details and discovering rare variants in genes that may suggest how they participate in causing AMD," Haines said.
The hope, Haines said, is that a full understanding of genetic and environmental risk factors will allow the computation of an AMD risk score. Several companies already offer tests that generate risk scores, but they are based on older information.
"If we can identify the people who are at greatly increased risk for AMD, perhaps we can begin to do clinical trials to test treatments that may prevent the disease," Haines said.
Current treatments for AMD help stabilize the disease, but they do not reverse its course. New treatments based on the genetic findings are in development, Haines said.
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