Dry age-related macular degeneration (AMD) may have a viral origin, according to new research in the August 28 online issue of the New England Journal of Medicine.

Researchers at Shiley Eye Center at the University of CaliforniaSan Diego, Johns Hopkins University and other institutions in the United States and China investigated the link between dry AMD and a key molecular proteintoll-like receptor 3 (TLR3)that alerts the immune system to the presence of viral infections. A genetic variant of TLR3 confers protection against dry AMD (i.e., geographic atrophy), probably by suppressing the death of retinal pigment epithelial cells, the researchers concluded.

This is the first gene that was discovered to be associated with the dry form of AMD. But, the researchers also suggest that an experimental therapysmall interfering RNA (siRNA)for the wet form of AMD could trigger this reaction in people with the genetic variant. In short, the researchers say, using siRNA to cure wet AMD might actually increase the risk for blindness from dry AMD. At least three drug companies (Opko Health, Allergan and Pfizer) are currently investigating siRNA drugs for wet AMD in human clinical trials. None have yet reported any toxic ocular effects.