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Ancient Viruses Embedded in Human DNA

a close up of a blue and purple structure

Around 8% of human DNA comprises genetic sequences from ancient viruses, known as human endogenous retroviruses (HERVs), dating back hundreds of thousands to millions of years. Recent research indicates that these viral remnants may influence susceptibility to psychiatric disorders like schizophrenia, bipolar disorder, and major depressive disorder.

HERVs are remnants of infections by ancient retroviruses, which inserted their genetic material into the DNA of infected cells. If these infections occurred in sperm or egg cells, the viral DNA was passed to subsequent generations, becoming part of our genetic lineage. Initially considered “junk DNA,” HERVs are now recognized for their roles in regulating gene expression and contributing to biological functions.

The Role of HERVs in Gene Regulation

Research has shown that HERVs can regulate the expression of neighboring genes, influencing important biological processes. For instance, some HERVs regulate genes involved in modifying connections between brain cells. HERVs can also produce RNA and proteins that perform various functions within the body.

HERVs and Psychiatric Disorders

Given the abundance and potential functions of HERVs in the genome, researchers have investigated whether genetic susceptibility to psychiatric disorders is linked to differences in HERV expression. A study analyzing nearly 800 autopsy brain samples identified DNA variations influencing HERV expression in the brain. Cross-referencing this data with genetic studies of individuals with and without mental health conditions revealed that the expression of four HERVs is associated with major psychiatric disorders. Specifically, two HERVs were linked to schizophrenia, one to both schizophrenia and bipolar disorder, and one to depression.

Implications and Future Research

While HERVs are just one piece of the complex puzzle of psychiatric disorders, this study highlights their significant role in the brain. The precise impact of HERVs on brain cells and their contribution to psychiatric conditions require further investigation. Although the practical applications of these findings are not yet clear, they offer a promising new direction for understanding and potentially treating psychiatric disorders. This research underscores the importance of exploring these ancient viral sequences, which have long been overlooked in genetic studies.

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