Chronic fatigue syndrome and the XMRV virus

There are many ways to fall prey to simplistic linear thinking when desperately seeking solutions to complex problems. Chronic Fatigue Syndrome can be a devastating illness; as attractive as a viral culprit may be to some, there is abundant evidence that attributing this complex condition to a singular cause unrealistically ignores the complexity of CFS and related conditions. A study just published in the Journal of Virology is the most recent 'nail in the coffin' for the notion that CFS is caused by the XMRV virus. The authors state:

"Chronic fatigue syndrome (CFS) is a multi-system disorder characterized by prolonged and severe fatigue that is not relieved by rest...Recently CFS has been associated with xenotropic murine leukemia virus-related virus (XMRV) as well as other murine leukemia virus (MLV)-related viruses, though not all studies have found these associations."

They analyzed blood samples from 100 CFS patients and 200 self-reported healthy volunteers using molecular, serological and viral replication assays. Interestingly, they also analyzed samples from patients in the original study that attracted so much media attention when it reported XMRV in CFS. What were the results?

"We did not find XMRV or related MLVs, either as viral sequences or infectious virus, nor did we find antibodies to these viruses in any of the patient samples, including those from the original study. We show that at least some of the discrepancy with previous studies is due to the presence of trace amounts of mouse DNA in the Taq polymerase enzymes used in these previous studies."

Attention to their conclusion may prevent clinicians and CFS sufferers from a fruitless diversion:

"Our findings do not support an association between CFS and MLV-related viruses including XMRV and off-label use of antiretrovirals for the treatment of CFS does not seem justified at present."

This is a thorough and detailed study, but is there any other evidence to support the assertion that we shouldn't depend on XMRV as a linear viral cause for CFS? A study recently published in the journal Retrovirology also finds no association in cases across the US:

"Here we tested blood specimens from 45 CFS cases and 42 persons without CFS from over 20 states in the United States for both XMRV and MuLV. The CFS patients all had a minimum of 6 months of post-exertional malaise and a high degree of disability, the same key symptoms described in the Lombardi et al. study. Using highly sensitive and generic DNA and RNA PCR tests, and a new Western blot assay employing purified whole XMRV as antigen, we found no evidence of XMRV or MuLV in all 45 CFS cases and in the 42 persons without CFS. Our findings, together with previous negative reports, do not suggest an association of XMRV or MuLV in the majority of CFS cases."

Additional research published shortly after in the same journal came up with the same negative results for both CFS and prostate cancer in Japan:

"To evaluate the risk of XMRV infection during blood transfusion in Japan, we screened three populations--healthy donors (n = 500), patients with PC (n = 67), and patients with CFS (n = 100)--for antibodies against XMRV proteins in freshly collected blood samples. We also examined blood samples of viral antibody-positive patients with PC and all (both antibody-positive and antibody-negative) patients with CFS for XMRV DNA."

Their data led them to the following conclusion:

"Our data show no solid evidence of XMRV infection in any of the three populations tested, implying that there is no association between the onset of PC or CFS and XMRV infection in Japan."

A study recently published in PLoS ONE (Public Library of Science) goes a step further in examining the issue. The authors state:

"The novel human gammaretrovirus xenotropic murine leukemia virus-related virus (XMRV), originally described in prostate cancer, has also been implicated in chronic fatigue syndrome (CFS). When later reports failed to confirm the link to CFS, they were often criticised for not using the conditions described in the original study. Here, we revisit our patient cohort to investigate the XMRV status in those patients by means of the original PCR protocol which linked the virus to CFS."

In addition to the PCR protocol used in the original study, the authors also assayed the sera of CFS patients for the presence of both the xenotropic virus envelope protein and a serological response to it. What did their data show?

"The results further strengthen our contention that there is no evidence for an association of XMRV with CFS, at least in the UK."

Subsequent research also conducted in the UK and published in PLoS examined a highly susceptible cohort of patients for XMRV virus:

"We extracted peripheral blood DNA from a cohort of 540 HIV-1-positive patients (approximately 20% of whom have never been on anti-retroviral treatment) and determined the presence of XMRV and related viruses using TaqMan PCR."

Even for this very vulnerable group XMRV was not proven to be a concern:

"In view of these negative findings in this highly susceptible group, we conclude that it is unlikely that XMRV or related viruses are circulating at a significant level, if at all, in HIV-1-positive patients in London or in the general population."

The authors of a study just published in the Annals of Neurology go a step further in investigating whether XMRV could be a causative agent in CFS. Having acknowledged the pre-existing research, they state:

"A useful next step would be to examine cerebrospinal fluid, because in some patients CFS is thought to be a brain disorder. Finding a microbe in the central nervous system would have greater significance than in blood because of the integrity of the blood–brain barrier."

The brain is at the core of the experience of fatigue; if the virus were to show up anywhere it should be there. What did they find?

"We examined cerebrospinal fluid from 43 CFS patients using polymerase chain reaction techniques, but did not find XMRV or multiple other common viruses, suggesting that exploration of other causes or pathogenetic mechanisms is warranted."

Just because a virus may be found in the body of a patient with CFS or any other condition does not mean that it is a significant causal factor for their complaint. The authors of a paper published in the British Medical Bulletin undertook a survey of...

"...All papers including the wording XMRV were abstracted from the NIH library of medicine database and included in the analysis."

They make the point that...

"An increasing number of papers now refute the association of XMRV with human disease in humans although there is some evidence of serological reactivity to the virus. While it is unlikely that XMRV is a major cause of either prostate cancer or CFS, it can infect human cells and might yet have a role in human disease."

But there is a big difference between being present in human cells and being a cause of disease. This is illustrated by a fascinating study published in the Journal of Virology showing that XMRV does not efficiently replicate and spread in human tissue. The authors state:

"To determine whether XMRV can replicate and spread in cultured PBMCs even though it can be inhibited by A3G/A3F, we infected phytohemagglutinin-activated human PBMCs and A3G/A3F-positive and -negative cell lines (CEM and CEM-SS, respectively) with different amounts of XMRV and monitored virus production by using quantitative real-time PCR."

They summarize their findings by concluding:

"We found that XMRV efficiently replicated in CEM-SS cells and viral production increased by >4,000-fold, but there was only a modest increase in viral production from CEM cells (<14-fold) and a decrease in activated PBMCs, indicating little or no replication and spread of XMRV...Overall, these results suggest that hypermutation of XMRV in human PBMCs constitutes one of the blocks to replication and spread of XMRV."

Wishing for a single linear cause that will lend itself to the discovery of a 'magic bullet' for conditions that are engendered by a multi-causal systemic web of factors is a flaw that has hindered progress in the treatment of chronic disease. In the case of CFS, dysregulation of the brain-immune axis is a core component. This demands that the clinician integrate a panoramic systems view with a nuanced investigation of individual functional elements. There is a world of science to delve into here; research just published in the journal NMR In Biomedicine offers a taste of the brain aspect. The authors in order to:

"...explore brain involvement in chronic fatigue syndrome (CFS), the statistical parametric mapping of brain MR [magnetic resonance] images has been extended to voxel-based regressions against clinical scores."

The compared MR signal levels in 25 CFS subjects and 25 normal controls, including such clinical scores as fatigue duration, another score based on the 10 most common CFS symptoms, the hospital anxiety and depression scale (HADS) anxiety and depression, and hemodynamic parameters from 24 hour blood pressure monitoring. What did their data show?

"In the midbrain, white matter volume was observed to decrease with increasing fatigue duration. For T1-weighted MR and white matter volume, group × hemodynamic score interactions were detected in the brainstem [strongest in midbrain grey matter (GM)], deep prefrontal white matter (WM), the caudal basal pons and hypothalamus. A strong correlation in CFS between brainstem GM volume and pulse pressure suggested impaired cerebrovascular autoregulation. It can be argued that at least some of these changes could arise from astrocyte dysfunction."

In other words, there were strong correlations between CFS symptoms and pathological changes in the brain. The authors conclude:

"These results are consistent with an insult to the midbrain at fatigue onset that affects multiple feedback control loops to suppress cerebral motor and cognitive activity and disrupt local CNS homeostasis, including resetting of some elements of the autonomic nervous system (ANS)."

How might such neurodegenerative changes come about? A paper published earlier in Autoimmunity Reviews discusses the autoimmune component of CFS:

"The current concept is that CFS pathogenesis is a multifactorial condition. Various studies have sought evidence for a disturbance in immunity in people with CFS. An alteration in cytokine profile, a decreased function of natural killer (NK) cells, a presence of autoantibodies and a reduced responses of T cells to mitogens and other specific antigens have been reported. The observed high level of pro-inflammatory cytokines may explain some of the manifestations such as fatigue and flu-like symptoms and influence NK activity. Abnormal activation of the T lymphocyte subsets and a decrease in antibody-dependent cell-mediated cytotoxicity have been described. An increased number of CD8+ cytotoxic T lymphocytes and CD38 and HLA-DR activation markers have been reported, and a decrease in CD11b expression associated with an increased expression of CD28+ T subsets has been observed."

The main point: practitioners and patients should not be seduced by the wish for a 'magic bullet' treatment of a single linear cause for complex conditions that require a systems biology perspective. In the case of chronic fatigue syndrome, the brain-immune axis comes to the fore, with all its multifaceted considerations for functional assessment and treatment.