‘More questions over link between XMRV and chronic fatigue syndrome’; ‘Nature’ news blog, May 05, 2011

From the ‘Nature’ news blog, 5 May 2011.

A comprehensive study on the purported link between XMRV and chronic fatigue syndrome (CFS) has failed to find any trace of the virus. The study published yesterday in the Journal of Virology also hints that contamination of laboratory reagents with mouse DNA may explain some of the previous positive results.

In 2009, a team led by Judy Mikovits at the Whittemore Peterson Institute for Neuro-Immune Disease in Reno, Nevada reported in Science the discovery of the retrovirus in up to two-thirds of patients with CFS, which is also known as myalgic encephalomyelitis (ME). The discovery raised the hopes of patients with CFS/ME because it offered a clear explanation for the mysterious condition, as well as hope of a treatment.

Over the last two years, however, the link between XMRV and CFS/ME has clouded considerably, and no lab has been able to replicate Mikovits’ results. I covered this saga in a recent feature, “Fighting for A Cause”, which included the revelation that XMRV was created in a laboratory in the 1990s and therefore was extremely unlikely to underlie CFS/ME.

Mikovits’s primary response has been that the studies failing to find XMRV have not replicated her lab’s methods precisely, which involved detecting virus genetic material, patient immune responses, as well as the ability of the virus to divide in cell culture.

The new study, led by Ila Singh at the University of Utah in Salt Lake City, has now done all that and still come up with no sign of XMRV in 100 CFS/ME patients as well as 200 healthy people. What’s more, Singh’s team failed to find the virus in 14 patients who previously tested positive for the virus in Mikovits’ lab. They also find evidence that mouse DNA contaminates some of the reagents used to search for XMRV DNA, offering a possible explanation for some positive results.

For a technical, yet highly readable explanation of Singh’s study, check out Vincent Racaniello’s Virology Blog, which covered the new paper yesterday.

Also significant is the fact that Singh has previously found XMRV in tissue from prostate cancer patients and shown that the virus is sensitive to antiretroviral drugs.

In the new paper, her team writes:

Given the lack of evidence for XMRV or XMRV-like viruses in our cohort of CFS patients, as well as the lack of these viruses in a set of patients previously tested positive, we feel that that XMRV is not associated with CFS. We are forced to conclude that prescribing antiretroviral agents to CFS patients is insufficiently justified and potentially dangerous.

While it’s tempting to call this paper the “nail in the coffin” for XMRV, other similarly thorough replication studies are in the works. The largest of those is a $1.3 million effort funded by the US National Institute of Allergy and Infectious Disease and being led by microbial epidemiologist W. Ian Lipkin at Columbia University in New York. Results from that study are expected by the end of this year.

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