A recent research paper that linked a retrovirus to chronic fatigue syndrome was fully retracted Thursday, following more than a year of growing doubts and incremental backpeddling by researchers and journals alike.

Subsequent studies by others and even retests by the original research team (led by Vincent Lombardi, of the Whittemore Peterson Institute in Reno) failed to replicate the finding, published in October 2009 in Science, which had pointed to the presence of XMRV (xenotropic murine leukemia virus–related virus) in blood samples from patients.

The validity of linking XMRV to chronic fatigue syndrome first attracted controversy less than a year after the paper's publication. A July 2010 paper in Retrovirology that failed to support the virus-syndrome link forced the researchers behind a newer replicating study that had been set for publication in Proceedings of the National Academy of Sciences (PNAS) to give their data another close look. The journal's decision to delay seemed only to raise more eyebrows, and PNAS Editor in Chief Randy Schekman said he was flooded with requests to publish the findings.

Then, two papers published in May in Science also failed to find the virus in other chronic fatigue patients, sounding a death knell for the theory. Editors at the journal issued a partial retraction of Lombardi's 2009 paper in September. Several of the original paper's authors agreed to rescind, but editors at the journal began to suspect "that a retraction signed by all of the authors is unlikely to be forthcoming."

The original findings were likely a result of contamination with mouse material. According to the retraction notice (pdf), "there is evidence of poor quality control in a number of specific experiments in the Report." Additionally, "the authors acknowledged to Science that they omitted important information" pertaining to one of the paper's key figures; the researchers had also failed to provide details about all of the substances with which they had treated patients' blood samples.

Retrovirologist Jonathan Stoye, of the National Institute for Medical Research in London, told a reporter at Nature magazine that "the writing's been on the wall for a long time."

For the million or so people in the U.S. who suffer from the elusive syndrome, the possibility that a retrovirus was to blame offered both an answer and the potential for treatment. Some doctors had already started putting patients on antiretrovirals, and the Red Cross had begun banning people with the disease from giving blood, to prevent potential contamination of supplies with the retrovirus.

The full retraction, published without all of the authors' consent, now once again casts wide open the search for causes behind chronic fatigue syndrome. And some researchers are already forging ahead in search of effective treatments for the difficult-to-diagnose condition. A study published in March in The Lancet found that a regimen of guided exercise and cognitive behavior therapy could "moderately improve outcomes for chronic fatigue syndrome."