A new study published on bmj.com today casts doubt on recent claims that a human retrovirus known as XMRV is linked to chronic fatigue syndrome or ME (myalgic encephalitis).
This is the third study to refute the original US study reporting the link.
Chronic fatigue syndrome is a debilitating condition that affects millions of people worldwide with disabling physical and mental fatigue that does not improve with rest. Its causes remain unclear, but many people say their illness started after a viral infection.
A recent study from the United States detected XMRV in two thirds of patients with chronic fatigue syndrome, but could not conclusively prove a direct (causal) link between the virus and the disease.
In January 2010, another research team found no evidence of XMRV in 186 patients with chronic fatigue syndrome in the United Kingdom. A third study, published earlier this month, also failed to identify XMRV in 170 patients.
So a team from the Netherlands, led by Professors Frank van Kuppeveld and Jos van der Meer, investigated whether this link could be confirmed in an independent European group of patients with chronic fatigue syndrome.
They examined the DNA from XMRV in the blood cells of 32 Dutch patients with chronic fatigue syndrome and 43 healthy controls, matched by age, sex and geographical area. Two highly sensitive tests were performed on two different target genes.
They found no evidence of XMRV in any of the patients or the controls, adding to the negative evidence in the two previous studies.
"Although our patient group was relatively small and we cannot formally rule out a role of XMRV, our data cast doubt on the claim that this virus is associated with chronic fatigue syndrome in the majority of patients," say the authors.
One reason why these results contradict the original findings may be that the US study involved patients from a specific outbreak of chronic fatigue syndrome in the mid-80s that has already been linked to several viruses, explain the authors. It is possible that XMRV is implicated in this outbreak, but does not play a substantial role in most cases of chronic fatigue syndrome elsewhere, they conclude.
To reconcile these different findings, other US laboratories are currently investigating XMRV and chronic fatigue syndrome, and the results are eagerly awaited, say researchers from Imperial College London and King's College London in an accompanying editorial.
"If the link fails to hold up, it will be another bitter disappointment to affected patients. Nonetheless, the current debate will still bring critical attention to the causes of chronic fatigue syndrome, and XMRV may turn out to be important in the pathogenesis of other diseases," they conclude.