Gene Linked To Alzheimer's Poses A Special Threat To Women
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Researchers say a gene could help explain why Alzheimer's disease affects more women than men. The gene increases the risk of developing Alzheimer's in both sexes, but a new study shows the increase is much more pronounced in women. NPR's Jon Hamilton explains.
JON HAMILTON, BYLINE: Women make up nearly two thirds of the people in the U.S. diagnosed with Alzheimer's. Michael Greicius, who studies memory disorders at Stanford, says that's something researchers have been wondering about for decades.
MICHAEL GREICIUS: And the question has always been is that simply an effect of, you know, the fact that women tend to live longer, they have increased longevity? Or is it that plus something else? And the jury is a little bit out still.
HAMILTON: Several large studies in the U.S. and Europe haven't settled the issue. So, Greicius and a team of researchers decided to take a different approach. They focused on men and women who carry a gene variant called APOE4 that puts them at high risk of developing Alzheimer's. Greicius says in the general population, about 15 percent of people have at least one copy of the APOE4 gene.
GREICIUS: And then, in Alzheimer's disease, the numbers are more like, you know, 50 or 60 percent. So it's really over-represented in Alzheimer's disease population.
HAMILTON: The team reviewed medical records of more than 8,000 older people. Some had the APOE4 gene. Some didn't. The records, many of them part of a data set funded by the National Institute on Aging, showed which people developed Alzheimer's disease over a three or four year period. And Greicius says when it came to the subset of people who carry the APOE4 gene, there was a clear pattern.
GREICIUS: In men there was really no increased risk in conversion over those three or four years that we followed them. Whereas in women the risk bumped up about twofold.
HAMILTON: Women with the gene were 1.8 times more likely than other women to develop Alzheimer's, or what's known as mild cognitive impairment. Greicius says the finding offers at least one reason, other than age, that women may be more vulnerable to Alzheimer's.
GREICIUS: Even when you control for their increased longevity, we believe that there is an increased risk for Alzheimer's in women. It may be that APOE4 is playing a sizeable role in this, but there are probably also other factors that contribute to this increased risk in women.
HAMILTON: Greicius says the finding about APOE4 is important for Alzheimer's researchers. But he still doesn't see any compelling reason for most of his patients, men or women, to find out whether they carry the gene.
GREICIUS: We've had a few people in their mid 50s come in that have one or two copies of the APOE4 gene, they're perfectly healthy, and they're asking us, what do we make of this?
HAMILTON: Greicius says he expects that question to become more common as the cost of genetic testing continues to decline.
Michelle Mielke, an Alzheimer's researcher at the Mayo Clinic, has high praise for the new study. But she says it still doesn't prove that women as a group are at greater risk for Alzheimer's.
MICHELLE MIELKE: What this highlights is that there are different risk factors for men and women. And in the field, we haven't really looked at that very closely.
HAMILTON: For example, Mielke says researchers are only beginning to understand the importance of factors like estrogen. She says some studies have suggested that when a woman's estrogen levels decline after menopause, her brain becomes more vulnerable to Alzheimer's.
MIELKE: What is interesting in relation to this paper is that particularly animal and cellular studies suggest that there is an interaction between APOE4 and estrogen. And so, that may possibly be explaining the findings we're seeing here in humans.
HAMILTON: In other words, it's the combination of lower estrogen levels and carrying the APOE4 gene that puts some women at risk.
Mielke says someday, understanding how Alzheimer's is different in men and women could lead to different drugs or preventive treatments. But at the moment, she says the advice for men and women concerned about the disease remains the same.
MIELKE: We say what's good for your heart is good for your brain. So exercise is good, controlling hypertension, cholesterol, eating right, doing physical activities, I think, are all important for your cognitive function.
HAMILTON: The new research appears in the Annals of Neurology. Jon Hamilton, NPR News.
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