So what is it going to take to get a proper and robust replication study done? Intense attention to detail. Because patient selection has been a potential confounding factor in the two negative studies, the scientific community must understand the clinical characteristics of the CFS patients who were XMRV positive in the Science paper. CFS is a chronic, heterogeneous illness with many possible subtypes each made even more complex by common co-morbidities such as irritable bowel syndrome, fibromyalgia and depression. The lack of universal subtypes, or staging criteria for severity and duration of illness makes comparisons challenging. Many CFS patients undergo a variety of treatments in order to get relief from this debilitating disease. Treatments, especially those that directly act on the immune system, may also affect the life cycle of XMRV and detection of the virus.
Standardization of testing methods must also progress. As we reported in January (
http://www.cfids.org/cfidslink/2010/010603.asp), the U.S. Department of Health and Human Services Blood XMRV Scientific Research Working Group is developing analytical panels that will allow multiple laboratories to standardize methods to optimize sensitive detection of XMRV proviral DNA and viral RNA. Once methods are standardized, these same laboratories plan to test coded panels of blood samples obtained primarily from healthy blood donors and from CFS patients who have been reported to be positive for XMRV.
Until methods are standardized and the scientific community is provided information about the specific characteristics of the CFS subjects (and controls) who tested positive in the Science paper, be prepared to read more negative studies. Hopefully the Science investigators will make this information available before interest in XMRV being associated with CFS fades and becomes yet another foiled attempt at solving CFS. Achieving scientific consensus on the role of XMRV in CFS certainly warrants more research and greater collaboration, as do so many other important discoveries being made.