Correction to This Article
The article about the discovery of three genes that affect a person's risk of developing Alzheimer's disease incorrectly identified Stephen Snyder as the deputy director of the National Institute on Aging. He is the deputy director of the institute's neuroscience division.

Scientists Discover 3 More Genes With Links to Alzheimer's Disease

By David Brown
Washington Post Staff Writer
Monday, September 7, 2009

Two European research teams have identified three genes that affect a person's risk of developing Alzheimer's disease, the most common cause of dementia in the elderly.

The new genes appear to have at least as big a role as four others discovered in the last 15 years that are known to play a role in Alzheimer's.

"The message here is that genes are important in Alzheimer's disease . . . and there may be multiple ways of reducing the risk that the genes produce," said Julie Williams, a neuroscientist at Cardiff University in Wales who helped lead one of the teams.

All so-called Alzheimer genes have normal roles in brain physiology; they don't exist solely to cause dementia. Instead, small variations in their DNA alter their function and, through processes only now being uncovered, increase or reduce a person's risk of developing the disease.

Two of the genes described in the new research may be involved in determining the brain's capacity to clear itself of toxic "amyloid" proteins that collect outside neurons, eventually poisoning them.

The most important previously known Alzheimer gene promoted overproduction of amyloid. The new findings suggest that at least two processes -- production of amyloid and its removal -- are involved in the disease.

At least 5 million Americans have Alzheimer's disease. By one estimate, one in seven people age 72 and older has dementia, with Alzheimer's the most common form.

The new findings, reported Sunday in the journal Nature Genetics, will have no immediate consequence in either diagnosis or treatment of the disease. However, they will help illuminate a process that goes on for years or even decades before memory loss, the cardinal symptom of the disease, becomes apparent.

The genes were found through "genome-wide association studies," in which long stretches of DNA are examined for small differences between individuals.

With the advent of cheap and fast DNA sequencing in the last five years, the studies have become a powerful way to uncover genes that make small contributions -- along with environmental influences and personal choice -- to a person's overall risk for such chronic ailments as diabetes, coronary heart disease and depression.

Neuroscientists believe 60 percent to 80 percent of a person's risk of developing Alzheimer's disease is attributable to genes. Knowing which they are and what they do may provide targets for drugs and other interventions.

"Hopefully they will point us to parts of a physiological pathway where we can do some tweaking," said Stephen Snyder, deputy director of the National Institute on Aging, who was not involved in the studies.

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