From the British Medical Journal, 22 December 2010 (Story by Jo Carlowe).
The XMRV virus, which has been implicated as a possible cause of chronic fatigue syndrome, is not the cause of the disease, an overview of four research papers has concluded.
The new findings, from researchers at University College London, the Wellcome Trust Sanger Institute, and the University of Oxford, show that cell samples used in previous research were contaminated with mouse DNA and that this was the source of the XMRV (xenotropic murine leukaemia virus-related virus). The papers are all open access and are available at www.retrovirology.com/.
The virus was first linked to chronic fatigue syndrome in a study published inScience in October 2009 (2009:326;585-9, doi:10.1126/science.1179052), which found that blood samples from patients with the syndrome carried traces of the XMRV virus.
The author of one of the studies, Greg Towers, a Wellcome Trust senior research fellow at University College London, said, “Our conclusion is quite simple: XMRV is not the cause of chronic fatigue syndrome.
“It is vital to understand that we are not saying chronic fatigue syndrome does not have a virus cause—we cannot answer that yet—but we know it is not this virus causing it.”
Professor Towers and his colleagues say that more rigorous methods are needed to prevent contamination of cell and DNA samples and that more consistent standards are required for identifying viruses and other organisms as the cause of a disease.
Paul Kellam, a coauthor and virus genomics group leader at the Sanger Institute, explained, “Increasingly we are using DNA based methods to accelerate our understanding of the role of pathogens in disease. These will drive our understanding of infection, but we must ensure that we close the circle from identification to association and then causation.
“The strongest lesson is that we must fully use robust guidelines and discriminatory methods to ascribe a cause to a disease.”
Reacting to the findings, Anthony Cleare, reader in affective disorders at the Institute of Psychiatry of King’s College London, said, “The original paper linking infection with the XMRV virus with chronic fatigue syndrome (CFS) received widespread publicity. However, if this latest paper is correct, and XMRV is a laboratory contaminant rather than a virus that infects humans, it could explain why later studies have not confirmed any link between XMRV and CFS. Patients with CFS need much more certainty before accepting a link between XMRV and their illness.”
Tim Peto, consultant in infectious diseases at the University of Oxford, said, “It came as a great surprise when XMRV was first suggested as being linked to chronic fatigue syndrome, and it was imperative that further tests be done to see if the findings could be repeated.
“There have now been a number of attempts which have failed to find the retrovirus in other samples, and this research suggests that in fact XMRV is probably a contamination from mouse DNA. These latest findings add to the evidence, and it now seems really very, very unlikely that XMRV is linked to chronic fatigue syndrome.”
A spokesman for the ME (myalgic encephalopathy) Association said that the organisation was keeping an open mind. He said, “Whether this study kills the theory that there is a close link between XMRV and chronic fatigue syndrome stone dead we just don’t know at this stage. There are still a large number of very serious investigations being carried out into this retrovirus, and the next set of results may show something completely different.”