Could Contemporary Psychiatric Disorders Be Linked to Ancient Viruses?

Ancient remnants of viral infections persist within the human genome, according to DNA researchers.

A recent study has uncovered that these ancient viruses still influence the brain and may contribute to contemporary psychiatric disorders.

Researchers at King’s College London have found that this ancient viral DNA increases vulnerability to conditions such as schizophrenia, depression and bipolar disorder.

Published in Nature Communications, the study reveals that approximately eight percent of the human genome comprises ancient viral fragments known as Human Endogenous Retroviruses (HERVs).

Previously considered "junk DNA," these viral fragments' locations and expressions in the genome, particularly in the brain, can now be precisely identified thanks to modern technology.

The study shows that specific HERVs expressed in the human brain contribute to susceptibility to mental health issues. The human genome, which contains 20,000 to 25,000 genes arranged along the DNA molecule, provides the genetic blueprint for our body's structure and function.

These genes are responsible for our inherited traits, physical characteristics, disease susceptibility and some behavioral traits.

Scientists from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London analyzed genetic data from tens of thousands of individuals with and without mental health conditions. They also examined 800 brain autopsies to find links between psychiatric disorders and HERV expression in DNA.

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While most genetic risk variations for psychiatric disorders affect genes with known biological functions, the researchers found that some of these risk factors specifically influence the expression of ancient viral DNA in the brain.

Five HERV expression signatures were linked to psychiatric disorders: two to schizophrenia, one to both bipolar disorder and schizophrenia, and one to depression.

“This study uses a novel and robust approach to assess how genetic susceptibility for psychiatric disorders impacts the expression of ancient viral sequences in the modern human genome. Our results suggest these viral sequences play a more significant role in the human brain than previously thought, with specific HERV expression profiles associated with increased susceptibility to some psychiatric disorders,” said Dr. Timothy Powell, co-senior author and senior lecturer at the IoPPN.