The once-promising belief that 2 retroviruses that cause leukemia in mice are potential causes of chronic fatigue syndrome in humans has been dismissed by findings from the most rigorous study to date on the link. In the study, published today in mBio, researchers found no evidence of infection with either xenotropic murine leukemia virus–related virus (XMRV) or polytropic murine leukemia virus (pMLV) infection in 147 patients with chronic fatigue syndrome.
Chronic fatigue syndrome is a disabling disorder characterized by persistent unexplained fatigue in association with impaired memory or cognition, muscle or joint pain, headache, sore throat, tender lymph nodes, and night sweats. In the United States, an estimated 42 people out of 10 000 have the condition, which results in annual direct medical costs as high as $7 billion.
For years, the existence of the condition has been met with skepticism by some in the medical community because of a lack of biological explanation for the disorder. An explanation, proposed in a 2009 article published in Science that linked XMRV to the syndrome, gave hope to those with the condition that it might be treated with drugs that are used to treat HIV, another infection cause by a retrovirus. Another study, published in early 2010 in the Proceedings of the National Academy of Sciences (PNAS), reported detecting pMLV in patients with chronic fatigue syndrome, which further bolstered the theory that the condition might be caused by a mouse virus. But the inability of other laboratories and the original researchers to replicate the XMRV or pMLV association with chronic fatigue syndrome lead to the Science article being retracted in December 2011.
In the mBio study, researchers (including some who worked on the original Science and PNAS studies) recruited 147 patients with chronic fatigue syndrome and 146 matched controls from 6 sites across the United States. The patients with chronic fatigue syndrome were between the ages of 18 and 70 years; had never suffered from another neurologic or psychiatric illness; had symptoms of a viral infection prior to the syndrome’s onset; had reduced quality of life; and were not pregnant, lactating, or less than 3 months postpartum. Blood samples from those with chronic fatigue syndrome and the control group were collected for blinded analysis of XMRV, pMLV, or both using molecular, culture, and serological methods. The study was commissioned by the National Institute of Allergy and Infectious Diseases.