Does XMRV Occur in People With Chronic Fatigue Syndrome? Studies Yield Mixed Results
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Reviewed By Laura J. Martin, MD
Sept. 9, 2010 -- An international group of scientists met this week at the National Institutes of Health to discuss a retrovirus that has been linked to chronic fatigue syndrome and prostate cancer. XMRV (xenotropic murine leukemia virus-related virus) was first identified in humans in 2006.
"We are at the very earliest stages" of understanding XMRV, said Cleveland Clinic urologist Eric Klein, MD, part of the team that discovered the virus in men with prostate cancer.
Studies in Confusion
Understanding the retrovirus was made more difficult over the past several months, as studies on the links between XMRV and chronic fatigue syndrome (CFS) were published with widely divergent results.
In the first study, published in the journal Science in October 2009, 67% of patients with CFS were infected with XMRV, while less than 4% of the control group tested positive for the retrovirus. Last month, a joint FDA/NIH study published in Proceedings of the National Academy of Sciences reported a strong link between CFS and a virus very similar to XMRV.
In the 10 months between the publication of those two studies, however, a report from the CDC and several other studies found no connection between CFS and XMRV.
"We're trying to hash out why the negative studies were negative," Klein said during a morning break. "There's debate about the robustness of the techniques used in the four negative studies as well as how the researchers defined CFS [when selecting eligible participants]."
More Questions Than Answers
At this point, experts are unable to say whether XMRV causes disease or whether it is a benign infection. Klein estimates that it will be a few years before there is enough evidence to answer such a basic question.
He compared what we know now about XMRV with what researchers understood about HIV at the beginning of the AIDS epidemic in the early 1980s.
"There was a great deal of skepticism about what caused the disease, and it took time to fit all of the pieces together," Klein said. "With XMRV, we're just gathering the puzzle pieces now."
SOURCES: Eric Klein, MD, urologist and chairman, Glickman Urological and Kidney Institute, Cleveland Clinic.
Lombardi, V. Science, Oct. 23, 2009; vol 326: pp 585-589.
Shyh-Ching, L. Proceedings of the National Academy of Sciences, Sept. 7, 2010; vol 107 (36): pp 15874-15879.
CDC: "XMRV: Questions and Answers."
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