Gene Linked to 'Dry' Macular Degeneration

Aug. 28 -- WEDNESDAY, Aug. 27 (HealthDay News) -- Scientists from the United States and China have identified the first gene directly associated with the onset of severe "dry" macular degeneration, one of two forms of age-related macular degeneration that currently threatens the vision of up to nine million older Americans.

The discovery, based on work with both human and mice cells, centers on a specific immune system protein called TLR3. Although helpful in fending off illness when confronted with certain viral infections, this molecule, when routinely activated, was also found to raise the risk for "dry" macular degeneration by attacking infected retinal cells.

But, the study authors also found a genetic silver lining in the form of a mutated version of TLR3 -- a so-called "inactive" or "less active" TLR3 -- that suppresses this retinal death process, seemingly protecting people from the eye disease.

"This represents a major step forward in our understanding of the dry form of macular degeneration," said study co-author Dr. Kang Zhang, a professor of ophthalmology and human genetics at the Shiley Eye Center at the University of California, San Diego, School of Medicine. "And with the identification of this potential target, we can try to develop treatments for a disease which, for the moment, we can't treat."

The findings were expected to be published online Aug. 28 in the New England Journal of Medicine.

But celebration over isolating TLR3's role in dry age-related macular degeneration (AMD) has been tempered by some potentially troubling implications that the new findings seem to have for a cutting-edge investigational treatment recently unveiled to target the so-called "wet" form of AMD.

The treatment in question, known as "RNA interference," or RNAi, works by "silencing" genes that bring about wet AMD. Unfortunately, the treatment appears to simultaneously activate TLR3 -- resulting in a 60 percent spike in retinal cell death among mice and humans genetically susceptible to developing dry AMD. The result: RNAi may help protect against wet AMD while boosting the risk for dry AMD, the study authors said.