The virus known as XMRV does not cause chronic fatigue syndrome.
Achieving this particular bit of knowledge has taken a pretty spectacular couple of years.
In October 2009, Judy Mikovits, a scientist then at the Whittemore Peterson Institute in Reno, Nevada, and her colleagues published a startling paper. They found that 68 out of 101 people suffering from chronic fatigue syndrome (also known as myalgic encephalomyelitis) carried a virus called XMRV. Only 8 out of 218 healthy people had it. That's 67% versus 3.7%. Mikovits and her colleagues raised the possibility that the virus played a part in the disorder, which affects an estimated 60 million people. If that were true, then there might be a straightforward way to treat people: wipe out the offending virus.
Very quickly, a number of other scientists replicated the experiment. One team found evdience of a different virus in some of their subjects--not XMRV. The other scientists couldn't find any virus at all that was present in any significant number of people with chronic fatigue and not in people without it.
With remarkable speed, the study and the follow-up research gave rise to a fierce controversy. Critics dismissed Mikovits's work as nothing more than contamination (the virus is common in mice). Mikovits dismissed her critics becasue they hadn't replicated her experiment closely enough to really test it. Many people with chronic fatigue syndrome, embittered by years of suffering (and suggestions that it was all in their head) rallied around Mikovits. (To get a sense of the back story, see the comments many people left on a blog post I wrote about this controversy last year.)
A few months into the controversy, I was at Columbia University to interview a scientist named Ian Lipkin for a profile for the New York Times. I focused mainly on his research linking viruses to new diseases. But Lipkin also does the reverse--what he likes to call "de-discovery." When someone makes a controversial claim that virus X causes condition Y, Lipkin sometimes puts the claim to the test. Lipkin explained to me how it's important to get everyone on board with such a replication study--both the original scientists and their critics. And he told me that he had launched a big study on XMRV, in collaboration with a team of scientists that included Mikovits, scientists who failed to find a link, and others. (I wrote more generally about de-discovery last year in the Times.)
The study would take a lot of time. The scientists and doctors would examine 147 people with chronic fatigue and 146 normal people, giving them thorough medical exams and a close inspection of their blood. Several labs would use identical methods to search for XMRV. And in that time a lot happened.
More scientists investigated XMRV on their own and found still more evidence that the viruses had likely contaminated Mikovits's cell cultures. Mikovits wouldn't budge, even as Science retracted the paper in December 2011. Meanwhile, Mikovits got into a battle royale with her institute, getting locked out of her office, sneaking in a grad student in to get her notebooks (possibly to work on Lipkin's study), and spending five days in jail.
Today, nearly three years after the start of the XMRV affair, the big study came out in the journal mBio. The scientists found no evidence of XMRV in people with chronic fatigue. Mikovits fully endorsed the conclusion.
I am curious how people with this condition view this finding. I find it pretty depressing. It's taken up plenty of money along with the valuable time of lots of talented researchers. It's raised and then dashed hopes. And all we have to show for it is the lack of a link. What causes chronic fatigue syndrome? Your guess is as good as mine.
It would be nice if there was a simple set of instructions for finding the cause, but that's probably just a fantasy. Perhaps the best we can hope for is to avoid these expensive, time-consuming wrestling matches in the first place. That's why I find projects like the Reproducibility Intiative so interesting. When scientists make mistakes, let's find out as fast as possible.
Here's some more information on the saga:
[Apologies for a few typos, now fixed--I hit "publish" instead of "save draft"!]