The Burrill Report


When researchers had discovered a virus to help explain a perplexing illness known as chronic fatigue syndrome, it provided hope for diagnosing and treating the disease. But a new study says that the research was wrong. It concludes the cell samples used to determine that the virus XMRV was connected to the disease were contaminated.

The new research, published in the journal Retrovirology, doesn’t rule out the possibility that a virus causes chronic fatigue syndrome, only that XMRV is not the culprit. It says the source of the XMRV in samples used to link the disease to the virus were actually mouse cells or mouse DNA rather than infection. XMRV is present in the mouse genome. An October 2009 study first linked XMRV to chronic fatigue syndrome. The virus has also been identified previously in samples from certain prostate cancer patients.

“All our evidence shows that the sequences from the virus genome in cell culture have contaminated human chronic fatigue syndrome and prostate cancer samples,” says Greg Towers, a Wellcome Trust senior research fellow at University College London. “It is vital to understand that we are not saying chronic fatigue syndrome does not have a virus cause–we cannot answer that yet–but we know it is not this virus causing it.”

The team, from University College London, Wellcome Trust Sanger Institute and University of Oxford, showed that the experimental design of previous studies would pick up sequences that resembled XMRV. They say, however, by using improved techniques they could prove that the signal was from contamination by a laboratory cell line or mouse DNA. They also showed that the existing methods would indicate that one in 50 human cell lines they examined were infected with XMRV-related viruses. They showed that contamination of human tumor cells with XMRV-related viruses is common and that a principal prostate cancer line used is contaminated.

“When we compare viral genomes, we see signs of their history, of how far they have travelled in space or time,” says Dr Stéphane Hué, a post doctoral researcher at UCL. “We would expect the samples from patients from around the world, collected at different times, to be more diverse than the samples from within a cell line in a lab, where they are grown under standard conditions. During infection and transmission in people, our immune system would push XMRV into new genetic variants.”

The authors propose that more rigorous methods are used to prevent contamination of cell and DNA samples. They also suggest that consistent and considered standards are needed for identifying viruses and other organisms as the cause of a disease.

“Increasingly, we are using DNA-based methods to accelerate our understanding of the role of pathogens in disease,” says Paul Kellam, virus genomics group leader from the Wellcome Trust Sanger Institute. “These will drive our understanding of infection, but we must ensure that we close the circle from identification to association and then causation.”


December 22, 2010
http://www.burrillreport.com/article-chronic_fatigue_alleged_culprit_questioned.html