A commonly used assay for XMRV, a virus that some believe may be associated with chronic fatigue syndrome and prostate cancer, is susceptible to contamination and may be yielding false positives, researchers reported yesterday.
Four independent groups found that even trace amounts of mouse DNA or RNA is all it takes to generate a positive signal from the assay, which relies on a technique called PCR to amplify specific regions of DNA. The findings could threaten the integrity of one line of evidence linking XMRV to disease.
That link was already controversial: two groups have reported finding XMRV and related viruses in samples from chronic fatigue syndrome patients, but several others have failed to reproduce the findings. Links to prostate cancer have been similarly contentious. The debate has left regulators uncertain as to whether blood donations from those with chronic fatigue could pose a threat to the blood supply. Meanwhile, some desperate chronic fatigue patients have been clamouring for anti-retroviral drugs in hopes that the treatments, which themselves carry significant side effects, could relieve their symptoms.
The four new papers, published yesterday in Retrovirology, are unlikely to end the dispute. Although the papers show that contamination is a serious threat to the integrity of the PCR-based assays for XMRV, researchers have also used other assays, some of which rely on antibodies specific to the viruses, to establish the link to disease.
“These data emphasize the importance of strict attention to molecular hygiene,” says Ian Lipkin of the Mailman School of Public Health and College of Physicians and Surgeons at Columbia University in New York. “They also raise concerns about some findings in earlier studies. However, they do not exclude an association between XMRV or related viruses with either prostate cancer or CFS.”
Lipkin is heading up an NIH project that unites three labs and six clinical sites to test the XMRV hypothesis. He says the team hopes to have results in about a year.
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