A much-anticipated paper on the potential role of retroviruses in chronic fatigue syndrome (CFS) just came out in The Proceedings of the National Academy of Sciences. Before it was published, many people had speculated that this work would “confirm” the XMRV-CFS link. It does not. However, it does provide more evidence that people with CFS may be more likely than the general population to harbor murine-like retroviruses.
As a Science news article covering the new work explains:
Part of the problem, skeptics say, is that the researchers didn’t exactly replicate the Science paper. XMRV is a so-called xenotropic murine virus, which means it can no longer enter mouse cells but can infect cells of other species. (Murine means “from mice.”) The researchers in the PNAS paper say the viral sequences they find are more diverse than that and resemble more closely the so-called polytropic viruses, which is why they adopted the term MLV-related virus, for murine leukemia virus. “Let’s be clear: This is another virus. They did not confirm [Mikovits's] results,” says retrovirologist Myra McClure of ICL, a co-author of one of the four negative studies.
Still, “in the grand scheme of things,” the viral sequence found in the PNAS paper closely resembles those of XMRV, says Celia Witten, the director of FDA’s Office of Cellular, Tissue and Gene Therapies, who was not an author of the paper herself but spoke on Lo’s behalf. Witten adds that the data “support” the Science paper. Mikovits — who is “delighted” by the new paper — says the difference is not important. In as-yet-unpublished results, her group finds more genetic diversity in the virus as well, she says.
So now we have two studies suggesting a correlation between CFS and murine-like retroviral infection, four studies finding no evidence of these murine-like viruses in any humans, and the newest results suggesting that we’re not dealing with a single virus at all, but perhaps a whole family of them. Interestingly, the two studies that did detect murine-like viruses in CFS found them in both CFS patients and healthy controls – they’re just much more frequent in the CFS patients. Similarly clear-as-mud data sets have now accumulated for prostate cancer, both claiming and denying a link between that disease and murine-like viruses.
This raises a whole passel of new questions. Are we simply awash in murine retroviruses, which can start opportunistic infections in humans who are already sick with other diseases? Do any of these viruses actually cause any disease? And if 3-6% of the healthy population really is walking around with these viruses in them, is there any point in restricting blood donations from CFS patients?