Updated

As scientists race to find a biological cause for chronic fatigue syndrome, long considered by many doctors to exist in patients' heads, the National Institutes of Health could shed new light on the debate at a major scientific workshop on the disorder.

Researchers at the University of Utah and elsewhere are working to create diagnostic tests, based partly on proteins or other markers that appear to show up in greater quantities in patients with chronic fatigue syndrome. Diagnosing the disorder is difficult, in part because symptoms vary among patients

Other scientists are trying to understand why other infections, such as mononucleosis, appear to prompt chronic fatigue syndrome in some patients. And in a program at New York's Columbia University, researchers are seeking to identify pathogens that may appear prominently in patients with the disorder.

Researchers will be testing "for all those agents that we know affect vertebrates on this globe," says Mady Hornig, who heads the Columbia program.

Chronic fatigue syndrome affects between one million and four million Americans. They suffer from memory and concentration problems, debilitating pain and severe fatigue. Unable to identify a cause, doctors often dismissed these patients as complainers.

CFS, also known as ME for myalgic encephalomyelitis, got a boost of attention in 2009 when the journal Science published a study that found the retrovirus XMRV was present in most members of a group of chronic fatigue syndrome patients. The 2009 study divided scientists and led to intense debate about whether the XMRV link is a breakthrough or a result of lab contamination. The study launched a wave of new research.

More than 100 scientists, researchers and advocates are expected to gather at the NIH workshop in Bethesda, Md., attending sessions focused on such medical topics as infectious diseases, systems biology, immunology and neurology. By contrast, the last NIH scientific workshop, in 2003, had more emphasis on the psychological aspects of the disease, including stress, insomnia and depression.

Medical history has other examples of diseases that were not taken seriously but later turned out to have biological causes. Multiple sclerosis was once misdiagnosed as hysteria or chronic alcoholism. Today multiple sclerosis is suspected to be an auto-immune disorder. Stomach ulcers were thought to be caused by stress until two Australian scientists proved the bacteria Helicobacter pylori was the cause, work that won the Nobel Prize in 2005.

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