Ancient viruses still linger in human DNA, and a recent discovery suggests that some may contribute to psychiatric disorders. Scientists from King’s College London identified five ‘fossil viruses’ linked to depression, schizophrenia, and bipolar disorder. These ancient viruses, known as Human Endogenous Retroviruses (HERVs), were previously considered ‘junk DNA’ with no functional purpose. However, this new understanding could pave the way for novel treatments for individuals suffering from these conditions.
The sequences of these ancient viruses are hundreds of thousands of years old, potentially dating back to Neanderthals. Dr. Timothy Powell, co-senior author of the study, explained, “This study uses a novel and robust approach to assess how genetic susceptibility for psychiatric disorders imparts its effects on the expression of ancient viral sequences present in the modern human genome. Our results suggest that these viral sequences probably play a more important role in the human brain than originally thought, with specific HERV expression profiles being associated with an increased susceptibility for some psychiatric disorders.”
The human genome consists of over six billion individual letters of DNA, similar to other primates like chimpanzees, spread across 23 pairs of chromosomes. To analyze a genome, scientists first chop the DNA into pieces hundreds to thousands of letters long. Sequencing machines then read the individual letters in each piece, and scientists assemble the pieces in the correct order, akin to solving an intricate puzzle.
The study analyzed data from large genetic studies involving tens of thousands of individuals, both with and without mental health conditions. The researchers also examined autopsy brain samples from 800 individuals to explore how DNA variations linked to psychiatric disorders affect the expression of HERVs, which make up about eight percent of the human genome. They found that some genetic risk variants partially influenced the expression of HERVs.
The five HERV expressions identified included two associated with schizophrenia, one linked to both bipolar disorder and schizophrenia, and one connected to depression. No HERV expressions were found to be associated with hyperactivity disorder or autism spectrum conditions.
Dr. Rodrigo Duarte, the study’s first author, remarked, “We know that psychiatric disorders have a substantial genetic component, with many parts of the genome incrementally contributing to susceptibility. In our study, we were able to investigate parts of the genome corresponding to HERVs, which led to the identification of five sequences that are relevant to psychiatric disorders. While it is not yet clear how these HERVs affect brain cells to confer this increase in risk, our findings suggest that their expression regulation is important for brain function.”
