XMRV and CFS

Two relatives of mine have recently been diagnosed with chronic fatigue syndrome (CFS). They are currently undertaking an experimental treatment prescribed by a doctor in Melbourne. I'll discuss more about the treatment and how it is supposed to work at a later time. For the moment I wish to discuss some interesting developments in the literature about a possible cause of CFS.

In 2009, Lombardi et al discovered that people with CFS had a significantly higher incidence of a recently discovered retrovirus, the xenotropic murine retro virus (XMRV), than a control group (no CFS). A year later, another study by Lo et al again found the presence of XMRV in many people with CFS and in few people in the control group. It was looking as though a possible relationship between the retro virus and CFS had been found.

Transmission electron microscopy image of XMRV (source: CDC)

The CDC (centre for disease control) in the USA published a report (Switzer2010) finding no significant detection of the retrovirus in CFS patients (theres a number of other journal articles with the same findings). Lo2010 puts it best:

"Further studies are needed to determine whether the same strong association with MLV-related viruses is found in other groups of patients with CFS, whether these viruses play a causative role in the development of CFS, and whether they represent a threat to the blood supply."

The editor in chief at PNAS wrote an editoral (Schekman2010) in September highlighting some concerns with the validity of the results in the Lo2010 paper in light of the Switzer2010 results.

Further to this, the November 15th, 2010 issue (its available online already.. I can't time travel yet!) of the Journal of Infectious Diseases has a number of papers addressing this issue. An editorial was written (Kearney2010) summarising the current state of play. It called from greater collaboration between different research groups and standardisation of detection techniques. It also has a crack at possible reasons the detection of the retrovirus varies significantly:

"Several factors may contribute to the varied detection of XMRV in different populations, including geographic distribution, patient selection, analyte choice(DNA, RNA, antigen), and detection methodology. Geography may play a pivotal role. Henrich et al [24] studied samples from immunodeficient patients who were well characterized at facilities in Boston and found no evidence of XMRV, whereas Lombardi et al [6] studied similarly affected patients from a distinctly different geographic region and found substantial rates of XMRV."

 The different studies did use different populations to gather their numbers. This could potentially have an impact, but it at least means that if XMRV is related to CFS, it is not ubiquitous. The old scientific adage "Correlation does not imply causation" comes to mind in this case. Is there other possible reasons why XMRV is present in people with CFS in some populations?
 
It seems as though there this is a very hot topic at the moment, considering the caliber of the journals that these articles are being published in. It seems there is still significant doubt whether the XMRV is linked with CFS. This will, in no doubt, be cleared up in the near future. I will try to post new developments about this as they come to hand.

If you'd like to read more, the CDC has a very nice updates and Q&A page.