On top of that, Reitz said, it is thought that there are probably many gene variants that each increase Alzheimer's risk by a small amount. No single gene variant is the whole story.
Ultimately, Nussbaum said, the hope is that gene studies will help reveal the underlying biological causes of Alzheimer's, and new treatments or preventive measures can be developed.
"The personal, emotional and financial cost of Alzheimer's is huge," Nussbaum said. "It should be a national priority to gain a better understanding of the disease."
It is estimated that about 5 million older Americans have Alzheimer's, and a recent study projected that without any strides in prevention, that number will triple by 2050.
"If we could figure out ways to delay Alzheimer's by even five years, that would have a big impact," Nussbaum said.
The study was funded by grants from the U.S. government, the Alzheimer's Association and drug maker GlaxoSmithKline. Nussbaum has financial ties to Complete Genomics, a company that does gene sequencing for researchers.
Learn more about Alzheimer's genes from the U.S. National Library of Medicine.
SOURCES: Christiane Reitz, M.D., Ph.D., assistant professor, neurology, Columbia University Medical Center, New York City; Robert Nussbaum, M.D., professor, medicine, University of California, San Francisco; April 10, 2013, Journal of the American Medical Association
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