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.
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