From ScienceNOW magazine, published by the American Association for the Advancement of Science, 16 February 2010 (Story by Sam Kean).
A theory linking chronic fatigue syndrome (CFS) to an infectious mouse virus known as XMRV has taken a second major hit. First proposed last October in Science, the virus-CFS connection was quickly challenged by a British group. Now a second team of British virologists reports that, after examining tissue from 170 CFS patients, they have failed to find evidence of XMRV.
Patients with CFS often report that their condition – a mix of symptoms including unexplained pains and excessive fatigue – began after an otherwise normal viral infection. And scientists in the past have preliminarily linked CFS to a few viruses. However, those links have fallen apart under scrutiny, and without a firm biological cause for CFS, victims continue to face skepticism that their condition is a “real” disease.
Researchers from the U.K. National Institute for Medical Research made the most recent challenge to the XMRV link, using PCR machines to hunt for DNA of the mouse virus in human tissue. As they reported 15 February in Retrovirology, they found no trace of the DNA in 299 samples taken both from CFS sufferers and healthy control patients.
The team also looked at blood serum from 565 people to see if they could identify signs of an immune response to XMRV. In this approach, the scientists did discover antibodies that fight XMRV in 26 people. However, only one of those people has CFS. The significance isn't clear, because the same antibodies can defend against other, related viruses, and the specific trigger in this case remains unknown. The main conclusion the authors draw is a firm maybe: “XMRV infection may occur in the general population, although with currently uncertain outcomes.”
The work corroborates a study published in January by a team at University College London, the first to challenge the mouse virus hypothesis. Both teams were responding to the work of a research group at the Whittemore Peterson Institute for Neuro-Immune Disease in Reno, Nevada, which reported finding XMRV in two-thirds of approximately 100 CFS patients. In unrelated studies, other researchers have linked XMRV–again controversially–to an aggressive form of prostate cancer.
Authors of the new paper offer some advice with their data: “Following the findings reported here,” they write, “it would seem a prudent next step for subsequent studies to compare samples and protocols between different laboratories around the world.”
That's a good idea, because discrepancies between labs are common, says David Griffiths, a virologist at Moredun Research Institute in Midlothian, United Kingdom, who has studied previous claims for retroviruses as the cause of chronic diseases. He also notes that he cannot find serious flaws with any of the published studies: “All the people involved are doing things exactly as they should be.” For the time being, then, the XMRV results will remain frustratingly ambiguous. As Griffiths says, “There must be an explanation for why disparate results are showing up, but it may not be an easy thing to turn up.”