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    Retrovirus Linked to Chronic Fatigue Syndrome

    XMRV Seen in 2/3 of CFS Patients; 10 Million in U.S. May Carry Virus
    WebMD Health News
    Reviewed by Louise Chang, MD

    Oct. 8, 2009 - Some 10 million Americans may carry a recently discovered retrovirus now linked to chronic fatigue syndrome.

    The virus, xenotropic murine leukemia virus-related virus or XMRV, was detected in 67% of 101 patients with chronic fatigue syndrome by Vincent C. Lombardi, PhD, of the Whittemore Peterson Institute in Reno, Nev., and colleagues.

    The researchers also found the virus in nearly 4% of healthy comparison subjects -- suggesting that millions of Americans may carry the mysterious virus, which was first detected in prostate cancers.

    "The discovery of XMRV in two major diseases, prostate cancer and now chronic fatigue syndrome, is very exciting. If cause and effect is established, there would be a new opportunity for prevention and treatment of these diseases," said Robert H. Silverman, PhD, of Cleveland Clinic's Lerner Research Institute, in a statement emailed to WebMD.

    Silverman is on of the team of scientists that first discovered XMRV, and was among the researchers linking the virus to chronic fatigue syndrome and prostate cancer.

    It's not yet proven that XMRV actually causes either chronic fatigue or prostate cancer.

    In prostate cancer patients, the virus is seen in patients who carry a genetic mutation that disables a key virus-fighting immune response. But the virus is seen in chronic fatigue patients with and without this mutation.

    Where did the virus come from? The virus is closely related to a retrovirus that's become part of the mouse genome. Oddly, XMRV cannot infect mouse cells -- but can easily infect human cells.

    It's unlikely that so many humans have caught XMRV from mice. It's more likely that the virus is spread from human to human, but how that happens remains to be seen.

    An editorial by John M. Coffin of Tufts University, Boston, and Jonathan P. Stoye of the Institute for Medical Research, London, accompanies the Lombardi report in the current issue of the online journal Sciencexpress.

    Coffin and Stoye note that if 4% of healthy people truly do carry XMRV, it means that the virus is astonishingly widespread.

    "If these figures are borne out in larger studies, it would mean that perhaps 10 million people in the United States and hundreds of millions worldwide are infected with a virus whose pathogenic potential for humans is still unknown," they write.

    What is known is that viruses closely related to XMRV do cause many different diseases -- including cancer -- in other warm-blooded animals.

    "Further study may reveal XMRV as a cause of more than one well-known 'old disease,' with potentially important implications for diagnosis, prevention, and therapy," Coffin and Stoye suggest.

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