Monday, August 23, 2010

Study: MLV Found In CFS Patients



# 4828



For years hundreds of thousands of people in the United States, and around the world, have been afflicted with a mysterious illness dubbed Chronic Fatigue Syndrome or CFS.  Symptoms vary, but usually include debilitating fatigue, fibromyalgia,  and often severe `brain fog’.


CFS first gained notoriety in the early 1990s, but has remained a difficult and controversial diagnosis.  It is basically a diagnosis of exclusion. 


If a patient has the right symptoms . . . and no other cause can be determined . . .they get lumped into the CFS pile.


Unfortunately, many doctors have refused to accept CFS as a legitimate illness, because no causative agent or pathogen has been identified.


Over the past year there have been several reports linking XMRV ( Xenotropic murine leukemia virus-related virus) - a retrovirus - to CFS patients, but that link has been tenuous and not borne out by every study.


Today, we’ve an announcement of a new study that found MLV Murine Leukemia Virus Related Gene Sequences – which are closely related to XMRV - in the blood of 87% of CFS patients tested, as opposed to just 7% of a control group.


While not proof of being the cause of CFS, this is a strong statistical link, which will doubtless give many CFS patients (and their doctors) reason to hope that perhaps our knowledge of this syndrome may be about to improve.



All of this, of course, means that more research is needed.   This study was embargoed until 3:00 EDT today, but already several media outlets have stories out on it.



Nature Blog has some background on this study, including why its publication was delayed for several months, in Delayed chronic fatigue syndrome paper to be published - August 23, 2010


The Wall Street Journal has additional coverage of this story with Study Finds Retroviruses in Chronic Fatigue Sufferers


The FDA news release on this story is below, followed by links to the PNAS article, and several media reports.


For Immediate Release: August 23, 2010

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:



The PNAS abstract has now appeared, and you may read it at:



Detection of MLV-related virus gene sequences in blood of patients with chronic fatigue syndrome and healthy blood donors

  1. Shyh-Ching Lo, Natalia Pripuzova  , Bingjie Li, Anthony L. Komaroff, Guo-Chiuan Hung, Richard Wang and Harvey J. Alter