Around 30 years ago, researchers in the UK discovered DNA strands of herpes simplex virus 1 in postmortem brain samples of Alzheimer’s patients at much higher levels than in healthy brains, hinting that viral infection could be somehow involved in the disease.
Since then, a string of studies has bolstered the association between Alzheimer’s disease and HSV1, as well as other pathogens, particularly the herpesviruses HHV6A and HHV6B, yet proving causality has remained elusive.
Now, in an extensive screen of hundreds of diseased brains from three separate cohorts, a collaboration of US-based researchers reports no evidence for increased RNA or DNA levels of HHV6A or HHV6B in tissue from people with Alzheimer’s disease relative to that from healthy individuals, contradicting the results of some previous results. The scientists also failed to find an association between transcripts of other viruses that have been linked to Alzheimer’s, such as Epstein-Barr virus and cytomegalovirus, and Alzheimer’s, they report [January 23] in Neuron.
“If their findings are correct, absence of HHV6 would make any involvement in Alzheimer’s disease unlikely,” although not impossible, [Alzheimer’s researcher Ruth Itzhaki] notes.