chronic fatigue syndrome (CFS) | Press Announcements > Study: Presence of murine leukemia virus found in CFS Patients, others

FDA Note to Correspondents

For Immediate Release: August 23, 2010
Media Inquiries: Shelly Burgess, 301-796-4651, shelly.burgess@fda.hhs.gov
Consumer Inquiries: 888-INFO-FDA



Study: Presence of murine leukemia virus related gene sequences found in CFS patients


Researchers have found murine leukemia viruses (MLV) related gene sequences in blood samples collected from patients diagnosed with chronic fatigue syndrome (CFS) and some healthy blood donors, according to a study published online today by the scientific journal Proceedings of the National Academy of Sciences (PNAS).

Investigators from the U.S. Food and Drug Administration’s Center for Biologics Evaluation and Research and the National Institutes of Health Clinical Center, in collaboration with a physician scientist at Harvard Medical School, examined blood samples from 37 patients diagnosed with CFS and from 44 healthy blood donors.

MLV is a type of retrovirus known to cause cancer in mice. Several different MLV gene sequences were identified in samples from 32 of the 37 patients with CFS (87 percent) and 3 of the 44 (7 percent) healthy blood donors. Investigators performed DNA sequencing on all positively amplified samples to confirm MLV like gene sequences.

This study supports a previous investigation [Lombardi et al. Science October 23, 2009 326: 585] that showed XMRV, a genetic variant of MLV-like viruses, to be present in the blood of people with CFS. The study demonstrates a strong association between a diagnosis of CFS and the presence of MLV-like virus gene sequences in the blood. The study also showed that MLV-like viral gene sequences were detected in a small fraction of healthy blood donors. Although the statistical association with CFS is strong, this study does NOT prove that these retroviruses are the cause of CFS. Further studies are necessary to determine if XMRV or other MLV-related viruses can cause CFS.

A previous study, published in 2009, reported finding XMRV infections in a high percentage of CFS patients and a small percentage of healthy blood donors. However,
several other studies from the United States (including a recent report from the Centers for Disease Control and Prevention), the United Kingdom, and the Netherlands have found no evidence of XMRV or other MLV-like viruses in the blood of people with CFS.

For more information:

► Murine Leukemia Virus Gene Sequence Study - Questions and Answers1
Safety & Availability (Biologics) > New study on the detection of murine leukemia virus-related virus gene sequences in the blood of patients with chronic fatigue syndrome (CFS) and healthy blood donors - Questions and Answers
Safety & Availability (Biologics) > New study on the detection of murine leukemia virus-related virus gene sequences in the blood of patients with chronic fatigue syndrome (CFS) and healthy blood donors - Questions and Answers


►► Xenotropic Murine Leukemia Virus-related Virus - Overview2 (CDC)
CDC - XMRV Home - XMRV


►►► Xenotropic Murine Leukemia Virus-related Virus - Questions and Answers3 (CDC)
CDC - Questions & Answers - XMRV


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Press Announcements > Study: Presence of murine leukemia virus found in CFS Patients, others


►► Xenotropic Murine Leukemia Virus-related Virus

XMRV is a newly identified human retrovirus that is similar to a group of mouse retroviruses (called murine leukemia viruses, or MLVs) scientists have known about for years. XMRV refers to xenotropic murine leukemia virus-related virus. It was first identified in 2006 in tissue samples from men with prostate cancer.

In a study published in the journal Science in October 2009, scientists reported a potential association of XMRV with chronic fatigue syndrome (CFS). In this study, XMRV was detected in approximately two-thirds of patients diagnosed with CFS. They also identified DNA of XMRV in the blood cells of some healthy persons and suggested a potential for XMRV transmission by transfusion or transplantation.

However, other recent studies, including a July 2010 research report from CDC scientists and colleagues at two other institutions, found no evidence of XMRV in CFS patients and in controls (see Updates).

More recently, investigators from the Food and Drug Administration (FDA), the National Institutes of Health (NIH), and Harvard Medical School published a report that presents evidence of MLVs in blood samples from CFS patients and healthy blood donors. The authors state that although they found a broader group of MLVs, rather than XMRV, their results support the 2009 report in Science. The FDA /NIH paper was published online August 23, 2010, in the Proceedings of the National Academy of Sciences.

The reporting of different findings from different studies is not uncommon. Various factors may have contributed to the differences in these studies, including selection criteria for inclusion of CFS patients, clinical complexities of CFS, and possible variations in XMRV and MLV infection rates among populations in different regions. Moreover, XMRV is a recently discovered virus and much remains to be learned about this and MLV-like viruses. As additional studies are done, it is possible that new findings may emerge that differ from what has been previously reported.

The potential role of XMRV and MLVs in causing diseases such as prostate cancer and CFS remains unknown at this time. Additional research is needed to further evaluate a possible link of XMRV and MLVs with negative health outcomes, including prostate cancer and CFS. If it is determined that XMRV and MLVs may have a role in causing disease and illness, prevention recommendations can be made.

Although it is presumed that XMRV can be transmitted through blood transfusion, no such transmission event has been identified, and there is no known evidence of XMRV or MLV infection or related illness or disease in transfusion recipients. Agencies within the Department of Health and Human Services (HHS) are conducting studies to determine the prevalence of XMRV in the blood donor population.

CDC, FDA, and NIH investigators have been collaborating with scientists from other agencies and groups with regard to XMRV and MLV research, and they will continue to do so. HHS agencies will keep the public updated and informed as more information becomes available.

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