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Ancient viral DNA in the human genome is linked to major psychiatric disorders
Last reviewed: 02.07.2025
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A new study led by King's College London has found that thousands of DNA sequences derived from ancient viral infections are expressed in the brain, some of which contribute to susceptibility to mental disorders such as schizophrenia, bipolar disorder and depression.
The work was published in the journal Nature Communications.
About 8% of our genome is made up of sequences called human endogenous retroviruses (HERVs), which are the products of ancient viral infections that occurred hundreds of thousands of years ago. Until recently, these “viral fossils” were thought to be simply “junk” DNA that had no important function in the body. However, thanks to advances in genomic research, scientists can now determine where these viral fossils are located in our DNA, allowing us to better understand when they are expressed and what functions they may serve.
This new study builds on these advances and shows for the first time that a set of specific HERVs expressed in the human brain contribute to susceptibility to mental disorders, marking a step forward in understanding the complex genetic components that contribute to these conditions.
Dr Timothy Powell, co-author of the study and senior lecturer at the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King's College London, said: "This study uses a new and robust approach to assess how genetic susceptibility to psychiatric disorders is influenced by the expression of ancient viral sequences present in the modern human genome. Our findings suggest that these viral sequences are likely to play a more important role in the human brain than previously thought, with specific HERV expression profiles associated with increased susceptibility to some psychiatric disorders."
The study analyzed data from large genetic studies involving tens of thousands of people with and without mental disorders, as well as information from brain samples taken at autopsy from 800 people, to examine how DNA variations associated with mental disorders influence the expression of HERVs.
Although most genetic risk variants associated with psychiatric diagnoses affected genes with well-known biological functions, the researchers found that some genetic risk variants preferentially affected the expression of HERVs. The researchers reported five robust HERV expression patterns associated with psychiatric disorders, including two HERVs associated with risk of schizophrenia, one with risk of both bipolar disorder and schizophrenia, and one with risk of depression.
Dr Rodrigo Duarte, first author and IoPPN Research Fellow at King's College London, said: "We know that mental disorders have a significant genetic component, with many parts of the genome progressively contributing to susceptibility. In our study, we were able to examine the parts of the genome corresponding to HERVs, leading to the identification of five sequences that are relevant to mental disorders. While it is not yet clear how these HERVs influence brain cells to cause increased risk, our findings suggest that regulating their expression is important for brain function."
Dr Douglas Nixon, co-author of the study and an investigator at the Feinstein Institutes for Medical Research at Northwell Health, US, said: "Further research is needed to understand the precise function of most HERVs, including those identified in our study. We believe that a better understanding of these ancient viruses and the genes known to be involved in mental disorders could revolutionise mental health research and lead to the development of new treatments or diagnostics for these conditions."