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Researchers say two common viruses appear to play a role in Alzheimer's disease. NPR's Jon Hamilton reports on a finding that could lead to new strategies for preventing and treating Alzheimer's.
JON HAMILTON, BYLINE: Like a lot of scientific discoveries, this one was an accident.
JOEL DUDLEY: Viruses were the last thing we were looking for.
HAMILTON: Joel Dudley is an associate professor at the Icahn School of Medicine at Mount Sinai in New York. He's part of a team that compared healthy brain tissue with brain tissue from people who died with Alzheimer's. The goal was to identify new targets for drugs. Instead, Dudley says, they found that the brain tissue from Alzheimer's patients contained a lot more virus.
DUDLEY: When we started analyzing the differences, it just sort of came screaming out at us from the data alone.
HAMILTON: Levels of two human herpes viruses were up to twice as high in brain tissue from people with Alzheimer's. These viruses are carried by almost everyone and are best known for causing a skin rash in toddlers, but they can also get into the brain. The team confirmed the association with Alzheimer's using data on hundreds of brains from a consortium of brain banks. Then, Dudley says, they tried to figure out how these viruses could be affecting the course of a brain disease.
DUDLEY: We almost mapped out the social network, if you will, of which genes the viruses are friends with and who they're talking to inside the brain and if the viruses are tweeting, who's tweeting back.
HAMILTON: And Dudley says what they found was really intriguing.
DUDLEY: Actually, a lot of well-known Alzheimer's genes came up as either interacting with the virus genes or being influenced by them.
HAMILTON: It's not clear exactly how virus genes interact with Alzheimer's genes, but Dudley says it is clear that the same genes that make some brains more susceptible to Alzheimer's also seem to make them prone to infection with these herpes viruses. And once the viruses get inside brain cells, they can just sit there quietly for decades until something causes them to wake up. Dudley thinks that's when the trouble starts.
DUDLEY: These viruses are becoming activated, and then they put gas on the flame of the Alzheimer's pathology.
HAMILTON: In other words, they speed up the formation of the plaques and tangles associated with Alzheimer's. Richard Hodes directs the National Institute on Aging, which helped pay for the research. He says the finding is important but not conclusive.
RICHARD HODES: The data are very provocative but fall short of showing a direct causal role of viral infection.
HAMILTON: But he says the evidence is good enough to merit a study looking at whether antiviral drugs can delay or prevent Alzheimer's. So the Institute on Aging is funding a study that will test this approach. Hodes says the new research on viruses also hints at another way to fight Alzheimer's. These herpes viruses appear to trigger an immune response in the brain that can accelerate the disease. So Hodes says it might be possible to protect the brain with drugs that tweak the brain's immune system.
HODES: The more we learn about the disease process and the more targets we can address, the greater the probability is we are going to make the impact that so far has eluded us in slowing or preventing the progression of Alzheimer's disease.
HAMILTON: The new research appears in the journal Neuron. Jon Hamilton, NPR News.
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