By testing a patient early on to see if they have the gene, they could then receive more targeted treatment and be fast-tracked for the most powerful medications.

London - The debilitating condition ME is not caused by viruses, according to a study which claims to dismiss this theory “once and for all”.

Hopes for a treatment were raised three years ago when researchers sensationally claimed that most cases of the illness – also known as chronic fatigue syndrome – may be triggered by little-known bugs in the blood.

Now experts say the latest study – which involved many of the same US researchers – provides conclusive evidence that this theory was wrong.

The research, at Columbia University in New York, found no evidence that sufferers are infected with the rare viruses XMRV or pMLV, which are distantly related to HIV.

It is believed that the 2009 study suggesting the link, which was published in a prestigious scientific journal, may have been flawed.

Similar studies at King’s College London and in the Netherlands have also failed to find evidence of the viruses in the blood of sufferers.

Co-author of the latest study Ian Lipkin, a professor of epidemiology, said: “We went ahead and set up a study to test this thing once and for all and determine whether we could find footprints of these viruses.

“We found no evidence of infection with XMRV and pMLV. These results refute any correlation between these agents and disease.” ME, or myalgic encephalomyelitis, affects 250,000 people in Britain and symptoms include extreme fatigue and muscle pain.

Some sufferers become so weak they are bedridden or confined to a wheelchair.

It was dismissed as “yuppie flu” in the Eighties and the lack of a clear cause led to scepticism it was a genuine illness. It was only properly recognised in 2002 when then chief medical officer Sir Liam Donaldson said ME was a “debilitating and distressing condition”.

In 2009 “spectacular” findings published in the journal Science pinned 70 percent of cases on the rare viruses, usually found in mice.

It is now thought these results may have been contaminated and the journal has retracted the research from the Whittemore Peterson Institute in Nevada.

This time researchers took “extraordinary care” to eliminate contamination in the chemicals used in the study, which tested the blood of 147 ME patients and a similar sized group of healthy volunteers.

Speaking of the findings, published in mBio, the journal of the American Society for Microbiology, Professor Lipkin said: “We’ve tested the XMRV/pMLV hypothesis and found it wanting.

“But we are not abandoning the patients. We’re not abandoning the science.”

Experts believe there may be a genetic cause for ME, or it may be triggered by a traumatic event or a weakness in the immune system. - Daily Mail