What Causes Macular Degeneration?

[Angel]

Findings in a recent study indicate 74 percent of age-related macular degeneration (AMD) patients carry certain variants of two genes -- Factor H and Factor B -- both of which significantly increase their risk of the disease.

Researchers at Columbia University Medical Center in New York examined the results of an earlier study, which established that several variants in the Factor H gene significantly increase the risk of developing AMD.

Factor H encodes a protein that helps shut down an immune response against bacterial or viral infection once the infection is eliminated. People with these inherited risk-increasing variations of Factor H are less able to control inflammation caused by infectious triggers, which may spark AMD later in life.

The investigators, however, found the effect of Factor H alone on AMD does not fully explain who gets AMD. Therefore, they decided to do a genetic analysis of 1,300 people and quickly identified Factor B as the major modifier of the disease. Biologically speaking, Factor H is an inhibitor, while Factor B is an activator, giving the genes complimentary roles. This means a person can have Factor H but a protective Factor B and as a result the person does not develop AMD. If a person has both a risk-increasing variant of Factor H and of Factor B, however, researchers are certain they will develop AMD.

"These findings are significant because they absolutely confirm the roles of these two genes and, consequently, the central role of a specific immune response pathway, in the development of AMD," says, Rando Allikmets, M.D., senior study author. "In just a few short years, we've gone from knowing very little about what causes AMD to knowing quite a lot. We now have clear targets for early therapeutic intervention."

More than 50 million people worldwide have irreversible blindness as result of macular degeneration, making it the most common cause of blindness for those over 60. It's estimated 30 percent of the population will have some form of AMD by the time they reach age 75.