Are herpes and Alzheimer's linked?

Henrietta Strickland
June 22, 2018

Instead, scientists say further work will test whether herpes virus activity is one of the causes of Alzheimer's.

A new study from a team at the Icahn School of Medicine at Mount Sinai has revealed an unexpected correlation between Alzheimer's disease and high levels of human herpes virus DNA.

"We know from several large population-based studies that nutrition is a key factor in the development of Alzheimer's disease, but attempts to identify an exact combination of nutrients that can positively impact on brain health have failed up until now", he said.

Joel Dudley, a geneticist and genomic scientist at the Icahn School of Medicine at Mount Sinai and senior author of the new paper, had not meant to investigate this theory when his lab began working on the newly published study in 2013. The brain is shown here as a complex network of interactions, with disruption of connections by the key viral species (HHV-6A, HHV-6B, HHV-7) identified in this study.Ben Readhead et al. The strains have been linked to encephalitis and other chronic conditions.

"I look at this paper and it makes me sit up and say, 'Wow,"' said Alzheimer's Association scientific programs director Keith Fargo. Something needs to activate the viruses, which causes them to begin replicating. While the findings are not causative, they do suggest an interaction between viral DNA sequences and the molecular, genetic, and clinical characteristics of AD. But the researchers, who published their findings Thursday in the journal Neuron, emphasize that their research doesn't prove that the viruses cause the onset or progression of Alzheimer's. Among the many challenges facing researchers is the fact that the earliest effects of the disease on vulnerable brain regions occur 20 or 30 years before memory loss, confusion, mood changes and other clinical symptoms appear.

"I don't think we can answer whether herpesviruses are a primary cause of Alzheimer's disease", says Dudley.

For the new study, which was broadly created to map and compare genetic, transcriptional, and protein networks underlying AD, the team analyzed whole exome DNA and RNA sequencing data from 622 brain donors with early- and later-stage clinical and neuropathological features of AD, and another 322 brains from donors without the disease, generated through the National Institutes of Health (NIH)-sponsored Accelerated Medicines Partnership for Alzheimer's Disease (AMP-AD). But the viruses also can get into the brain, where they may remain inactive for decades. But we were able to perform a more sophisticated computational analysis using multiple levels of genomic information measured directly from affected brain tissue.

This is especially true because HHV-6A and HHV-7 are extremely common and often latent or asymptomatic: in North America, nearly 90% of children have one of these viruses circulating in their blood by the time they're a few years old. In fact, in North America it is estimated that 90 percent of children have at least one of these viruses in their blood early in life. It usually causes a fever and sometimes a rash and rarely causes complications, although it can cause a unsafe brain inflammation called encephalitis.

The herpes viruses also seem to trigger an immune response in certain brain cells, Hodes says.

Herpes viruses 6 and 7 are widely present in humans, but poorly understood.

Researchers say their findings suggest that a controversial hypothesis that viruses are involved in dementia may be correct.

It's nearly certainly the case that these viruses have been in the bodies of the affected people for a long time, said Fargo.

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

Other reports by Click Lancashire

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