Virus Theory for Chronic Fatigue Syndrome Discredited
XMRV Virus Probably Not a Cause of CFS; Original Study Partially Retracted
Testing for XMRV
XMRV is a retrovirus that is closely related to viruses that cause cancer in mice. It was first discovered in 2006 in samples from men with prostate cancer.
For the new study, nine laboratories used three different kinds of tests to re-screen 15 people who had once tested positive for XMRV and 15 healthy people who had been found not to carry the virus.
Two of the laboratories involved in the study were also involved in the 2009 paper, which reported finding XMRV in 67% of chronic fatigue syndrome patients compared to just 4% of healthy people, suggesting that the virus could be a cause of the chronic, debilitating condition.
So that the labs could be sure their tests were working correctly, they were also given blood samples that were spiked with small amounts of XMRV.
All the labs were able to find XMRV in these prepared samples, indicating that the testing methods they were using were valid.
But only two of the labs found evidence of mouse retroviruses, including XMRV.
The researchers, Busch says, were unable to detect the virus at higher rates in those CFS patients compared to people that their labs agreed were negative. "I take that as an indication that those results are unreliable.”
Time to Move On?
Patient advocates say it's time to refocus research efforts on credible science.
“We share the deep disappointment of many CFS patients and scientists that the initial data did not hold up. Whether you have been diagnosed recently or have been ill for decades, this news comes as a blow to hope for rapid advances in the care available to CFS patients,” says Kim McCleary, president & CEO of the CFIDS Association of America, in a prepared statement.
“There are many other solid leads that merit the same rigorous follow-up as XMRV has received over the past two years,” McCleary says.
Since the original paper was published in 2009, 17 published studies have tried but failed to confirm the findings of the original report.
Two studies, published earlier this year in Science, found evidence that XMRV had contaminated many of the cell lines and laboratory products used by researchers to test patient samples, skewing the results of several studies that linked the retrovirus to chronic fatigue syndrome and prostate cancer.
Mikovits says the cell line used in her laboratory and in the laboratory of her co-author, Frank W. Ruscetti, of the National Cancer Institute, has never been grown in mice and is thus uncontaminated.
However, samples handled by two of her co-authors in the original paper from 2009 did test positive for contamination. Test results based on those contaminated samples were retracted by co-authors from the findings of the 2009 paper.
In an unsigned statement supporting the partial retraction, the researchers say they now agree that XMRV was unlikely to be a cause of chronic fatigue syndrome.
“We encourage patients to talk with their doctors about approved treatments for symptoms and disease progression,” the statement says.