Thousands of DNA sequences resulting from ancient viral infections are active in the brain, and some of them contribute to susceptibility to psychiatric disorders such as schizophrenia, bipolar disorder and depression. This was revealed by a study by King’s College London published in Nature Communications.
8% of our genome is composed of sequences called Human Endogenous Retroviruses (HERVs), which are products of ancient viral infections that occurred hundreds of thousands of years ago. Until recently, it was thought that these “fossil viruses” were simply junk DNA, without any important function in the body. However, scientists have discovered where these fossil viruses are located in our DNA, allowing us to better understand when they are active and what functions they might have.
The new study is the first to demonstrate that a specific set of HERVs active in the human brain contributes to susceptibility to psychiatric disorders, marking a step forward in understanding the complex genetic components that foster these conditions.
The study analyzed data from large genetic studies involving tens of thousands of people, both with and without mental health conditions, as well as information from autopsy brain samples of 800 individuals, to explore how DNA variations linked to psychiatric disorders influence the activity of HERVs. The researchers found that certain genetic risk variants for mental disorders preferentially affected HERV activity. The researchers reported five HERV activity profiles 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.
Psychiatric disorders have a substantial genetic component, with many parts of the genome contributing to increased susceptibility. The study identifies five ‘fossil’ genetic sequences relevant to psychiatric disorders. While it is not yet clear how these HERVs influence brain cells to confer this increased risk, the findings suggest that regulation of their activity is important for brain function.
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