A new paper published online in Science on Thursday has failed to confirm a link between a mouse retrovirus called XMRV and chronic fatigue syndrome. Along with the new study, the authors of the controversial original study that first associated the virus with the illness in 2009 published a partial retraction of that work.
For the new study, conducted by the Blood XMRV Scientific Research Working Group, researchers analyzed blood samples from 15 people who had previously tested positive for XMRV or a similar mouse leukemia virus; 14 of these people had chronic fatigue syndrome (CFS) and one person had contact with a patient with the disease. The researchers also looked at 15 blood samples from healthy donors who did not have XMRV or CFS.
The samples were blinded and sent to nine different labs — including the Whittemore Peterson Institute lab and a National Cancer Institite lab, which participated in the 2009 study — for testing for XMRV. Seven labs could not find XMRV or any related viruses in the blood samples. The two labs that were involved in the original research did find the retroviruses, but they didn’t find them in the same people and they were equally likely to find the viruses in controls as well as those who had earlier tested positive. Neither lab was able to replicate its own findings.
The origins of chronic-fatigue syndrome, which causes severe pain, exhaustion and memory and concentration problems, and has no cure, have long been a mystery. Studies have fingered immune system inflammation, the herpes virus and the Epstein-Barr virus as possible culprits. But there is no definitive cause, and many sufferers of the disease say that doctors don’t always believe they’re sick.
When the 2009 paper was published in Science, it came as a great relief to people with CFS — an estimated 1% of the world population — and to the scientists who study it. If a cause could be identified, then it could open the door to potential treatment.
But since that time, the original research has repeatedly come under fire. Seventeen studies have been published since the 2009 paper, showing no link between XMRV and chronic fatigue. One particularly damning study published in May found that the retrovirus found in the original blood samples got there by laboratory contamination.
All 13 of the authors of the 2009 study signed the partial retraction published in Science on Thursday. However, Judy A. Mikovits of the Whittemore Peterson Institute in Reno, Nev., which led the original research team, said the initial work deserved continued follow-up study. The Wall Street Journal reported:
Dr. Mikovits said she stood by the theory that there was a retrovirus associated with chronic-fatigue syndrome, though not necessarily XMRV. “We have to dig in to find the right viruses. We need to keep looking,” she said.
Many other experts, including Kim McCleary, president and CEO of the Chronic Fatigue and Immune Dysfunction Syndrome Association of America, said they thought it was time to move on to other lines of research.
“We share the deep disappointment of many CFS patients and scientists that the initial data did not hold up. Whether you have been diagnosed recently or have been ill for decades, this news comes as a blow to hope for rapid advances in the care available to CFS patients,” McCleary said in a statement.
Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.