An international team of researchers claims to have identified the first gene associated with severe, "dry" macular degeneration, the main cause of vision loss in adults aged 60 or over.

The finding, spearheaded by Dr. Kang Zhang of the Shiley Eye Center at the University of California San Diego School of Medicine in La Jolla, focused on a molecular protein called toll-like receptor (TLR3), which is believed to play a key role in the innate immune system. The study, published in the August online issue of the New England Journal of Medicine, says that TLR3 activation causes the death of specific cells in the retina and that individuals with the normal TLR3 gene are up to five times more likely to have geographic atrophy than individuals who have an inactive TLR3 gene mutation.

Scientist found that, when activated, the protein increased the risk for "dry" macular degeneration by harming the infected retinal cells.

"Because of speculation among scientists that viral infections provoke the inflammation that increases the risk of macular degeneration, we tested for associations between AMD and TLR3, which is known to support innate immunity and host defense," said Dr. Kang Zhang, lead researcher of the study and professor of ophthalmology and human genetics at Shiley Eye Center.

According to Nico Katsanis, Zhang's partner in the study and an associate professor of ophthalmology, molecular biology, and genetics at the Johns Hopkins School of Medicine, if the molecules "are too sensitive towards viral insults, they might kill cells a little too eagerly, and that might be a predisposing factor that leads to macular degeneration."

Estimates say more than 6 million Americans suffer from AMD, which causes a graded loss of central vision. There are two types of the disease: dry and wet. Blindness from dry AMD occurs progressively over the course of many years, light-sensitive macular cells starting to stop working. And wet AMD (advanced AMD) involves rapidity of vision loss because of the development of abnormal blood vessels under the macula, triggering leakage of blood and fluids, The Washington Post reported.