Human endogenous retroviruses, or HERVs, are remnants of viral genes found in the human genome. These ancient viruses were embedded in human DNA millions of years ago and have been linked to an increased risk of depression, schizophrenia, and bipolar disorder. A recent study by Timothy Powell and colleagues at King’s College London found that individuals with a higher genetic risk for these mental health conditions also have unusual activity levels in the viral genes.
Retroviruses are a type of virus that inserts its genetic information into the DNA of its host during its life cycle. While HERVs were previously thought to be dormant “fossil viruses,” recent studies have suggested that some of these viral genes may be active and could potentially play a role in neurological conditions like multiple sclerosis.
In their study, Powell and colleagues examined viral proteins in nearly 800 brain samples to investigate the role of HERVs in mental health conditions. Although the donors of the brain samples were not diagnosed with mental health conditions during their lives, the study found that certain genetic variants associated with depression, schizophrenia, and bipolar disorder were linked to altered activity of genes from five different HERVs.
While the study did not quantify the exact increased risk associated with the altered viral gene activity, Powell estimates it to be around a few percent, as most genetic variants only have a small impact on psychiatric risk. The findings do not definitively indicate that altered HERV activity causes these conditions; it could be a consequence instead. Experts like Rachael Tarlinton at the University of Nottingham acknowledge the robust methods used in the study but caution that the significance of these findings is still unclear.
