A Note on XMRV
In 2009, researchers from the Whittemore Peterson Institute (WPI) published a study in the journal Science that suggested a link between XMRV, a newly discovered retrovirus, and ME/CFS. They found XMRV in about 67% of blood samples from ME/CFS patients. They also detected it in 3% of healthy controls.
However, subsequent studies failed to confirm the link, including a large study involving the WPI's primary researcher. Other studies suggested means by which contamination may have created false positives in the original study. By late 2011, the XMRV theory had been all-but abandoned.
Immune System Abnormalities
Several studies have shown irregularities in the immune systems of people with ME/CFS, but researchers have not found a consistent pattern of abnormalities. Among the most common are allergies and an overactive immune system.
Some studies have reported that a majority of ME/CFS patients are allergic to things including pollen, foods and metals such as nickel and mercury. That's led to a theory that allergens may trigger a series of immune abnormalities which then lead to ME/CFS. One theory is that allergies, stress and infection may combine to deplete a chemical called adenosine triphosphate (ATP), which stores energy in cells. Some ME/CFS patients show evidence of decreased ATP production.
Some ME/CFS patients have high levels of a substance called cytokines, which scientists theorize could cause symptoms of ME/CFS, including fatigue and muscle aches. Various studies have reported T cell imbalances in people with ME/CFS, but other studies have not confirmed the T cell and cytokine abnormalities.
While chronic fatigue syndrome appears to have a few features in common with autoimmune diseases such as lupus or multiple sclerosis, in which the immune system mistakenly attacks healthy parts of the body, most researchers now believe ME/CFS is probably not caused by autoimmunity. Tests of people with ME/CFS do not show markers of the organ damage generally associated with autoimmune disease.
Stressful Conditions
Researchers believe your psychological makeup, personality and social situation can impact whether you'll develop ME/CFS, but they don't yet fully understand the complex relationship between them. While these factors are probably not a primary cause of ME/CFS, they're likely to play a role in making you susceptible.
Note: ME/CFS is not considered a primary psychological illness, nor does having ME/CFS mean someone is psychologically weak or unable to cope with things. While it is sometimes linked to clinical depression, ME/CFS is a distinct condition.
Chemicals and Environmental Toxins
In one subgroup, chronic fatigue and pain are associated with exposure to various chemicals and environmental toxins. These can include solvents, pesticides or heavy metals. However, because most of us have been exposed to these types of chemicals at some point, it's difficult to track down which ones might be causing problems. A condition called multiple chemical sensitivity (MCS) causes many of the same symptoms as ME/CFS, and the two are believed to be overlapping conditions.
Sources:
2006 Centers for Disease Control and Prevention. "Possible Causes"
Dr. J.K.S. Chia. Copyright 2005 Co-Cure. All rights reserved. "The role of enterovirus in chronic fatigue syndrome"
Kaiser J. Science. 2011 Jan 7;331(6013):17. Chronic fatigue syndrome. Studies point to possible contamination in XMRV findings.
Lombardi VC, et al. Science. 2009 Oct 23;326(5952):585-9. Detection of an infectious retrovirus, XMRV, in blood cells of people with chronic fatigue syndrome
Nater UM, et al. Journal of clinical endocrinology and metabolism. 2008 Mar;93(3):703-9. Attenuated morning salivary cortisol concentrations in a population-based study of persons with chronic fatigue syndrome and well controls.
Simmons G, et. al. Science. 2011 Nov 11;334(6057):814-7. Failure to confirm XMRV/MLVs in the blood of patients with chronic fatigue syndrome: a multi-laboratory study.
Vernon, S. Pharmacogenomics, April 2006; vol 7: pp 345-354. The challenge of integrating disparate high-content data: epidemiological, clinical and laboratory data collected during an in-hospital study of chronic fatigue syndrome.
