E2 ModerateModerate confidencePEM ?Cross-SectionalPeer-reviewedMachine draft
Murine gammaretrovirus group G3 was not found in Swedish patients with myalgic encephalomyelitis/chronic fatigue syndrome and fibromyalgia.
Elfaitouri, Amal, Shao, Xingwu, Mattsson Ulfstedt, Johan et al. · PloS one · 2011 · DOI
Quick Summary
Researchers tested whether a virus called XMRV (xenotropic murine retrovirus) was present in Swedish patients with ME/CFS and fibromyalgia. Using sensitive tests on blood samples from 78 ME/CFS patients and 168 healthy blood donors, they found no evidence that this virus was present in any of the samples. This study helps answer questions about whether XMRV plays a role in ME/CFS.
Why It Matters
XMRV was proposed as a potential pathogen in ME/CFS, generating significant hope and controversy. This rigorously controlled study from an independent laboratory in Sweden contributes to the broader scientific debate about XMRV's role in ME/CFS, helping researchers understand geographic variation in viral findings and informing future investigations.
Observed Findings
- No samples from 78 ME/CFS patients tested positive for XMRV/HMRV using multiple PCR assays.
- No samples from 168 Swedish blood donors showed evidence of XMRV/HMRV.
- Three different published XMRV/HMRV PCR assays showed conspicuous differences in predicted and observed amplification ranges.
- The integrase-specific PCR was strictly XMRV-specific rather than detecting the broader murine gammaretrovirus group.
Inferred Conclusions
- XMRV/HMRV-like proviruses belong to a defined third murine gammaretrovirus group that can be characterized and detected by PCR.
- XMRV/HMRV was not present in detectable levels in blood samples from Swedish ME/CFS patients with or without fibromyalgia.
- Methodological differences among published XMRV PCRs may explain some conflicting findings reported in the literature.
Remaining Questions
- Why do different geographic populations and laboratories report different rates of XMRV detection—is this due to true geographic variation, methodological differences, or contamination?
- Could XMRV be present in tissues other than blood (such as cerebrospinal fluid, gut, or nervous tissue) even if absent from circulating cells?
- Are there other viral candidates or pathogens that might better explain ME/CFS etiology?
What This Study Does Not Prove
This study does not prove that XMRV does not exist in any ME/CFS patients anywhere—it only shows absence in this Swedish cohort. It does not exclude the possibility that XMRV might be present in tissues other than blood, at very low levels, or in patients from other geographic regions. Negative PCR results cannot definitively rule out a pathogen's involvement in disease.
Tags
Biomarker:Blood Biomarker
Method Flag:Weak Case DefinitionSmall SampleExploratory Only