From the ‘New Scientist', 23 September 2011 (story by Andy Coghlan)
Researchers who claim they have found a link between a mouse leukaemia virus and chronic fatigue syndrome (CFS) have partly retracted their paper published two years ago in the journal Science.
The partial retraction was prompted by a new analysis of 15 out of the 43 blood samples from people with CFS that tested positive for xenotropic murine leukaemia virus-related virus (XMRV) in the original analysis.
Both the retraction and the new analysis have just been published in Science, which last October printed an “editorial expression of concern” about the research. The journal has also previously published two other papers undermining the original study, although the authors of the original study are standing by the parts of the paper contributed by other groups.
In the new analysis, the 15 samples that originally tested positive for the mouse virus and 15 control samples were sent to nine independent laboratories – including three labs involved in the original study – to see if they could detect the virus.
The six labs unconnected with the original study all drew a blank. The three labs that originally detected XMRV detected it again, but also found it in the control samples – which had been confirmed in advance to be virus-free. Also, these three labs produced inconsistent results when they assayed samples split into different fractions for validation testing – some tested positive for the virus and some didn't, even though they were parts of the same original sample.
Fail to detect
“The most important finding is the inability of the three labs that previously reported detection of these viruses in CFS patients to accurately detect these viruses,” says Michael Busch of the Blood Systems Research Institute in San Francisco, California, lead author of the new analysis.
In their retraction, Robert Silverman and Jaydip Das Gupta of The Cleveland Clinic, Ohio, say that some of the blood DNA they analysed turned out to contain loops of XMRV DNA called plasmids. These plasmids are thought to have originated from prostate cancer cell experiments between 1993 and 1996 which subsequently contaminated the three labs. These, they say, account for the anomalous results.
Busch and his colleagues from the five other labs that failed to detect the virus say that the findings add to the mounting evidence that it is not the cause of chronic fatigue syndrome, otherwise known as ME (myalgic encephalomyelitis). “I think it is very unlikely that XMRV or related mouse leukaemia viruses are involved in chronic fatigue syndrome,” he says.
A further study by Ian Lipkin of Columbia University in New York is under way, and could provide more robust evidence that the mouse viruses are not to blame. “We need to wait for the Lipkin study results to definitely conclude that these viruses are not linked to CFS,” says Busch.
Myra McClure of Imperial College London conducted a study in the UK last year that found no trace of the virus in people with CFS – one of almost a dozen to have done so since 2009. She applauds Silverman for the retraction. “Bob Silverman is a good scientist and an honourable one,” she says. “I guess he can only retract the figures that he contributed to the original paper.”
Journal reference: Science, DOI: 10.1126/science.1213841