Dashing the hopes of many people with chronic fatigue syndrome, an eagerly awaited study coordinated by government health agencies has not confirmed a link between the illness and a virus called XMRV or others from the same class of mouse leukemia viruses.
Two research groups had earlier reported an
association between chronic fatigue syndrome and the group of viruses, known as
murine leukemia viruses, or M.L.V.’s, raising hopes that a treatment or cure
could be found. But later studies did not substantiate the link, and many
researchers suggested that that the initial findings were the result of
contamination of laboratory samples or equipment.
The new multilab
study, published online Thursday in the journal Science, was designed to answer
some of the questions about these unusual viruses and determine whether they
posed a risk to the blood supply.
Results from another
government-sponsored study of M.L.V.’s, with a much larger sample size, are
expected early next year. But Thursday’s report appeared to leave little room
for continued optimism.
Of the nine labs that received blinded blood
samples from 15 people previously reported to have been infected with M.L.V.’s
and 15 healthy controls, only two reported finding evidence of the viruses in
any of the samples. And the results from those two labs — which were the only
two to find positive results in the original studies — contradicted not only
each other this time, but some of their own earlier findings as well.
“These results indicate that current assays do not reproducibly detect
XMRV/M.L.V. in blood samples and that blood donor screening is not warranted,”
reported the new study, written by researchers participating the Blood XMRV
Scientific Working Group.
But the scientists also said they could not
“definitively exclude” the possibility that levels of viral markers in the blood
might fluctuate over time and become undetectable at certain periods.
Also on Thursday, researchers from the original study linking XMRV to
chronic fatigue syndrome, which was published in Science in October 2009,
retracted a portion of their data — but not their conclusions — because of
evidence of contamination in one lab involved in the study.
Racaniello, a microbiology professor at Columbia University who has covered the
controversy on his popular virology blog, said the XMRV/M.L.V. hypothesis was
now dead. “It’s clearly time to move on in the study for the origin of this
disease,” he wrote in an e-mail message.
An estimated one million
Americans suffer from chronic fatigue syndrome. Countless studies have
documented immunological, neurological and other physiological abnormalities.
Despite the name of the illness, patients have long reported that simple fatigue
is not their cardinal symptom but rather what researchers call postexertional
exhaustion — a profound depletion of energy after even minimal exercise or
Recently, a panel of top researchers proposed a new definition
of the illness that requires the presence of postexertional exhaustion, rather
than the six months of unexplained fatigue required under the standard
The group also recommended changing the name to myalgic
encephalomyelitis, a virtually identical illness long recognized by the World
Dr. Nancy Klimas, an immunologist at the University
of Miami, said that the two-year debate over M.L.V.’s had raised the profile of
the disease and brought attention to the likely role of infectious agents in
chronic fatigue syndrome.
“Internationally recognized experts have
looked at the immune data and concluded that there very well may be a pathogen
or pathogens involved in the persistence of this illness,” Dr. Klimas wrote in
an e-mail message.
The new findings will also be presented Friday in
Ottawa at the annual conference of the International Association for Chronic
Fatigue Syndrome/ME, a leading scientific organization