Human endogenous retroviruses are remnants of viral genes in the human genome
NICOLLE R. FULLER/SCIENCE PHOTO LIBRARY
Ancient viruses that embedded themselves in human DNA millions of years ago may play a role in increasing people’s risk of developing depression, schizophrenia and bipolar disorder. A study finds that viral genes show abnormal levels of activity in people who are at higher genetic risk for developing these psychiatric disorders.
Retroviruses are a large family of viruses whose life cycle includes inserting their genetic information into the DNA of their host. Remnants of such viral genes can be found in the DNA of many animal species, and when these sequences are found in the human genome, they are called human endogenous retroviruses (HERVs).
Until recently, most HERVs were thought to be dormant and referred to as “fossil viruses.” But previous research has shown that some viral genes may actually be active—although not producing infectious virus—and may even play a role in neurological diseases. For example, multiple sclerosis.
In a new study, Timothy Powell Researchers at King’s College London and their colleagues investigated the role these viral remnants might play in mental health conditions by looking at viral proteins in nearly 800 brains donated for medical research.
While the team did not record whether any of the donors had been diagnosed with mental health disorders during their lifetime, they found that some genetic variants known to increase the risk of depression, schizophrenia and bipolar disorder were associated with altered activity in five different HERV genes.
Powell said it’s impossible to estimate how much abnormal viral gene activity is associated with an increased risk of disease, but it’s probably in the range of a few percent because most human gene variants have only a small effect on psychosis risk.
The findings don’t necessarily mean that changes in HERV activity are the cause of these conditions — it could be a consequence, he said.
“The methods used appear to be very reliable,” Rachel Tarrington University of Nottingham, U.K. “The results may well be true that these things are markers of these diseases, but (the researchers) are right to be cautious in saying they don’t know what that means.”
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