Doubts over chronic fatigue syndrome and links to the XMRV virus, thought to be responsible for the condition, have been raised by a new research study.

Results from nine different labs around the United States failed to differentiate patients with chronic fatigue syndrome from healthy controls solely on the basis of whether they tested positive for xenotropic murine leukemia virus-related virus (XMRV).

As per the new study, XMRV virus may not be the cause. The failure in discovering evidence of XMRV infection in some of the same patients involved in the study is raising questions as to whether this virus is the cause of chronic fatigue syndrome.

The study is partially retracting from the authors of the 2009 study that first pointed to XMRV as a probable cause of chronic fatigue syndrome.

When the 2009 paper was published in Science, it came as a great relief to people with CFS - an estimated 1 percent 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.

The new study was published in the September issue of Science. All 13 of the authors of the 2009 study signed the partial retraction published in Science on Thursday.

Severe and continued tiredness that is not relieved by rest and is not directly caused by other medical conditions refers to chronic fatigue syndrome. Symptoms of chronic fatigue syndrome are similar to those of the flu and other common viral infections, and include muscle aches, headache, and extreme fatigue.

An estimated one million Americans suffer from chronic fatigue syndrome.