Chronic fatigue syndrome (CFS) causes severe fatigue that can last for months at a time. CFS is difficult to diagnose and even more difficult to treat, and its cause has long been a mystery. In 2009, in an apparent breakthrough, scientists reported that a virus found in mice, called XMRV, might be the long-sought cause of chronic fatigue. Their results were reported, with great fanfare, by Judy Mikovits and colleagues in the journal Science (Lombardi et al., Science 2009;326:585), with reports in respected outlets such as the New York Times making it seem that the answer had been found.
Now it turns out that, like many initially exciting reports, this one has a much more mundane explanation: contamination.
As happens all too often when a “surprising” discovery is announced, the result turns out to be an experimental error. Contamination is a common type of error in modern molecular genetics, because nothing is actually visible to the naked eye, and we have to rely on very sensitive methods (such as PCR) to detect what is present. In this case, the experimenters had a common mouse cell line in their lab (not unusual), and it turns out these mouse cells were contaminated with a virus called MLV, which looks a lot like XMRV.
The new study by Hue et al. from University College London (Retrovirology 2010, 7:111) is titled “Disease-associated XMRV sequences are consistent with laboratory contamination.” The title pretty much tells the story, but here’s a brief synopsis.
The first report that a retrovirus might be the cause of Chronic Fatigue Syndrome came out about a year and a half ago. But very quickly came conflicting reports that the retrovirus was not involved.
Now comes what appears to be the definitive answer – the supposedly specific tags used to identify the retrovirus actually cross reacted with another similar virus. And this other virus was found to contaminate cells in the labs doing the work.
The original paper presented some data that they interpreted as signifying that XMRV could be a cause of disease. Others then went out to verify this and showed that the original interpretation was wrong.
This is how science works. The thing that Feynman talked about was that scientists need to be aware of how easily they can be fooled and to strive to make sure that all controls have been done.
Here, we have a case of a lab that did not seem to fully perform this self-examination. They should have been the ones to find the contamination, rather than have others do it.
But whether done by the original scientists or by others, science works towards finding out what is really happening.
Now if only the media would realize the tentative nature of most science.