A new study of chronic fatigue syndrome (ME/CFS) sufferers has found no evidence for the presence of xenotropic murine leukemia–related virus (XMRV) in their spinal fluid, casting doubts on findings of other researchers that suggested XMRV may be at least one causative factor in this complex condition.
In 2009, Judy Mikovits Ph.D. and colleagues at the Whittemore Peterson Institute (WPI) in Reno, Nevada, published results showing that a retrovirus, XMRV, was common in ME/CFS patients but not in healthy individuals. The finding brought ME/CFS into the full glare of the media spotlight for the first time; the condition having previously been considered a 'fad' diagnosis by many.
Since the publication of this landmark study from the WPI scientists around the world have been trying to replicate the findings. In 2010 The Food and Drug Administration (FDA) and National Insititutes of Health (NIH) confirmed the WPIs findings, at least to a point. Other scientists, particularly outside the US, have however failed to find any evidence that XMRV is more common in blood samples from chronic fatigue syndrome patients than it is in samples from healthy controls.
The new study was conducted by Steven E. Schutzer, MD and colleagues at the University of Medicine and Dentistry of New Jersey, Newark, and their findings are reported in the Annals of Neurology.
Dr. Schutzer and his team enrolled 43 individuals in their study who met the widely used Fukuda criteria for a diagnosis of ME/CFS. Each study participant had samples of their spinal fluid taken and this was analysed using a technique known as polymerase chain reaction (PCR) which amplifies genetic material and in this case would make detection of viral DNA/RNA easier. No evidence of XMRV or other common viruses were found by the researchers.
The use of spinal fluid as the target for testing in this study can be explained by previous observations that many symptoms of ME/CFS include a neurologic component and spinal fluid may therefore contain relevant pathogens associated with the condition. Another consideration was the fact that the brain and central nervous system (CNS) represent a relatively enclosed system. When viruses are found in the blood it is hard to know whether they are the cause of a disease, or present due to poor immunity resulting from the disease. Many viruses, particularly those of the herpes familly (Epstein-Barr (EBV), Human Herpes Virus 6 (HHV-6)), have been found in ME/CFS previously and suspected to be the cause but this has not turned out to be the case.
According to the researchers, "Spinal fluid is a liquid window to the brain. It is an important area of the body to examine when there is abnormal central nervous system (CNS) function and an infectious or immunologic cause is suspected."
Most previous studies have only looked for XMRV in the blood which may have contributed to some of the contradictory results thus far. This may be the first study to look for the presence of XMRV solely in the CNS through analysis of spinal fluid.
According to Dr. Schutzer, "This latest study was not designed to address the ongoing controversy over possible XMRV in the blood. It was specifically designed to survey the central nervous system for XMRV and, if found, other viruses."
Dr. Schutzer and colleagues say that the detection of viruses and other pathogens is only the first step and recommends further research to validate infection as the cause of ME/CFS. Many researchers and physicians remain a healthy scepticism with regards to a purely infectious cause for the condition. While it is the case that a large proportion of patients report a stubborn viral infection that "never went away" as being the initial trigger for their illness, others say that different factors such as an acute pesticide exposure were to blame.
Dr. Schutzer and his team encourage a prospective search for microbes and other possible causes of chronic fatigue syndrome, with particular attention paid to the CNS. Meanwhile, the debate over the role of XMRV will go on as investigations continue.