Another study finds no link between mouse virus and chronic fatigue syndrome

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For the second time in as many months, researchers have been unable to replicate a controversial study which showed that many patients with chronic fatigue syndrome carry a virus that might be linked to the disease. Researchers are now trying to figure out whether the discrepancies result from studying different patient populations or from fundamental problems between the laboratories involved.

Chronic fatigue syndrome, also known as chronic fatigue and immune dysfunction syndrome (CFIDS), is thought to affect at least 1 million Americans and more than 17 million worldwide. It is characterized by debilitating fatigue, chronic pain and depression, in addition to other symptoms. Many doctors, however, have argued that it is not a real disorder because there are no characteristic biochemical markers that define it. The only effective treatments have been behavioral changes and antidepressants, and they have been of limited benefit.

Sufferers were overjoyed last October, therefore, when researchers from the Whittemore Peterson Institute for Neuro-Immune Disease in Reno reported in the journal Science that they found a mouse virus called xenotropic murine leukemia virus-related virus, or XMRV, in blood from 68 of 101 patients with chronic fatigue syndrome, but in only eight of 218 healthy patients. In a separate study, researchers reported that they found the virus in about a quarter of prostate cancer patients. At last, it seemed, science was moving toward finding a cause for the perplexing disorder.

In January, however, a team from University College London reported in the journal PLoS One that they could find no trace of the virus in blood samples from 186 chronic fatigue patients. Critics charged that the lab’s assays were not sensitive enough to identify the virus.

Now, virologist Kate Bishop of the MRC National Institute for Medical Research (Britain’s equivalent of the U.S. National Institutes of Health) and her colleagues have reported in the journal Retrovirology that they too could not find the virus, this time in 170 chronic fatigue patients and 395 controls. Outside researchers agreed that their tests should have been sensitive enough to detect the virus if it was present.

The contradictions have left many experts confused. Virologist Suzanne D. Vernon, scientific director of the CFIDS Assn. of America, argues that part of the problem may lie in the type of patients chosen. The new study used patients who had been diagnosed for less than four years and whose disease was relatively mild. The first study, in contrast, involved patients who had suffered longer and had more serious forms of the disorder. She also argues that more standardization between laboratories needs to be achieved. Until that occurs, she says, confusion will continue to reign.

-- Thomas H. Maugh II