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Alzheimer’s disease may be triggered by herpes virus, scientists suspect

Sarah Knapton
Researchers found large amounts of viral DNA in key areas of the brains of Alzheimer's patients  - Redhead et al

Alzheimer’s disease may be triggered by the herpes virus, a new study suggests, leading to hopes that antiviral medication could help prevent dementia.

Around 850,000 people are living with dementia in Britain, and the majority of people have Alzheimer’s which occurs when sticky plaques of amyloid build up in the brain, killing brain cells.

But new research has found that the brains of people who have died of Alzhiemer’s have almost double the level of HHV-6A and HHV-7 herpes virus as non-diseased brains, suggesting it is playing a role in the condition.

Researchers in the US believe that the disease may trigger an immune ‘cascade’ which encourages the growth of amyloid plaques.

It raises hopes that cases could be prevented through antiviral drugs.

How herpes in the brain could trigger Alzheimer's 

The team did not set out to study the impact of herpes, but were looking for anything which might be different in six key brain regions in people with Alzheimer’s compared to those who were dementia free.

They began by sequencing DNA from the dead patients to find out information about inherited genes, followed by their RNA to find out how those genes were expressed.

“We didn't go looking for viruses, but viruses sort of screamed out at us,” said lead author assistant research professor Ben Readhead of Arizona State University.

“We saw a key virus, HHV 6A, regulating the expression of quite a few Alzheimer’s risk genes and genes known to regulate the processing of amyloid, a key ingredient in Alzheimer’s neuropathology."

The study authors say the findings suggests that Alzheimer’s could be ‘collateral damage’ caused by the brain's response to the virus.

Both HHV 6A, and 7 are common herpesviruses and most people are exposed to them early in life. It is different from the Herpes-simplex virus which causes cold sores and genital herpes.

The level of the virus in the brain also correlated with clinical dementia scores before death. Those with more viral DNA performed worse in tests.

“I don't think we can answer whether herpesviruses are a primary cause of Alzheimer's disease,” said study senior author, Dr Joel Dudley, Director of the Institute for Next Generation Healthcare at the Icahn School of Medicine at Mount Sinai. 

“"But what's clear is that they're perturbing and participating in networks that directly underlie Alzheimer's.

"This study represents a significant advancement in our understanding of the plausibility of the pathogen hypothesis of Alzheimer's

 "If it becomes evident that specific viral species directly contribute to an individual's risk of developing Alzheimer's or their rate of progression once diagnosed, then this would offer a new conceptual framework for understanding the emergence and evolution of Alzheimer's at individual, as well as population, levels."

Commenting on the study Prof Clive Ballard, Professor of Age-Related Diseases, University of Exeter Medical School, said: “This new study is a vital step forward as it highlights specific disease related mechanisms.  

“This now gives the potential to investigate the impact of viruses more directly in experimental studies, so that we can really understand whether there may be important implications for treatment or prevention.”

Prof Ruth Itzhaki, Professor Emeritus of Molecular Neurobiology at the University of Manchester, and Honorary Senior Research Fellow at the University of Oxford, added: “A picture is building up showing strong links between herpes viruses and the likelihood of developing Alzheimer’s disease.  

“We now need more research to establish whether these viruses are causally linked to Alzheimer’s, and whether using that information we might be able to develop treatments.”

The research was published in the journal Neuron.

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