May 5th

Study Finds No Link Between XMRV and Chronic Fatigue Syndrome

There have been a number of studies that failed to replicate a study published in Science in 2009 that found the virus XMRV in a greater proportion of CFS patients than in healthy controls. But today’s paper, published online in the Journal of Virology, is significant because the researchers took pains to address some of the problems that plagued previous negative studies.

“We basically did everything we could think of to come up with a positive result,” Alan Light, one of the study authors, tells the Health Blog.

The authors also include Ila Singh, who has previously published papers finding XMRV in prostate-cancer patients. Singh could not be immediately reached for comment. (Today’s study does not address the question of whether XMRV is linked to prostate cancer.)

The researchers took blood from 100 CFS patients and 200 healthy volunteers who all lived in the same geographic area, Salt Lake City. The patients all met the criteria specified by the so-called Canadian definition of chronic fatigue syndrome, which clinicians prefer to use. Over 70% of the patients said their CFS began with a flu-like illness, suggesting a viral trigger to their condition.

The blood samples from both patients and controls were taken and processed in parallel. In addition, a third-party phlebotomy service collected blinded blood samples from 14 patients who had previously tested positive at the Whittemore Peterson Institute lab, which led the team of researchers on the original Science paper.

Using highly sensitive tests, the Utah scientists said they could not find XMRV or other viruses in the same family in either patients or controls. They did not find antibodies to XMRV. They did not find infectious XMRV in the plasma of patients or controls. Light says the team has been working on the study for a year.

The Whittemore Peterson Institute’s Judy Mikovits, who led the research team on the Science paper, tells the Health Blog she has not yet read the complete study. She says XMRV isn’t fully understood. And she also says that one of the statements in today’s paper is incorrect. She tells Health Blog that not all of the 14 people who previously tested positive for XMRV were part of the original Science paper; only two of them were.

Light says in response: “The 14 patients who previously tested positive were all selected by Judy.”

One of the issues raised after negative studies were published is how to explain how some patients still test positive for antibodies to XMRV even though the virus itself can’t be found in their blood.

Vincent Racaniello, a Columbia University virologist who wrote about today’s study on his blog, tells us that to perform antibody tests, proteins from the virus are used. He says that other viruses have proteins that are highly related to XMRV proteins. If the patients then test positive for antibodies, “it looks like they have antibodies to XMRV but they are not specific to that virus.”

Racaniello says he considers today’s paper important because it took such a comprehensive approach, but he adds that he expects the controversy to continue. More studies that may resolve the debate regarding the virus and CFS are in the works.

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