People with ancient viruses in their DNA are more prone to depression, study reveals

Ancient viruses are still lingering in human DNA, but a new discovery has found that some may contribute to psychiatric disorders.

Scientists from King’s College London identified five ‘fossil viruses’ associated with depression, schizophrenia and bipolar disorder.

The ancient viruses, called Human Endogenous Retroviruses (HERVs), have been previously known but were seen as ‘junk DNA’ with no purpose – but could now lead to new treatments for those suffering with such conditions.

Researchers said that the sequences are hundreds of thousands of years old, meaning they could have originated in Neanderthals. 

Dr Timothy Powell, co-senior author, said: ‘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 is made up of just over six billion individual letters of DNA – about the same number as other primates like chimps – spread among 23 pairs of chromosomes.

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To read a genome, scientists first chop up all that DNA into pieces hundreds to thousands of letters long.

Sequencing machines then read the individual letters in each piece, and scientists try to assemble the pieces in the right order, like putting together an intricate puzzle.

The study analyzed data from large genetic studies involving tens of thousands of people, both with and without mental health conditions.

The team also used information from autopsy brain samples from 800 individuals to explore how DNA variations linked to psychiatric disorders affect the expression of HERVs, which make up to eight person of the human genome.

Researcher then found that some genetic risk variants partially affected the expression of HERVs. 

With the five expressions identified, the team found two associated with risk for schizophrenia, one associated with risk for both bipolar disorder and schizophrenia, and one associated with risk for depression. 

The team noted that no HERV expressions were found associated with hyperactivity disorder and autism spectrum conditions.

Dr Rodrigo Duarte, first author, said: ‘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. 

‘Whilst it is not clear yet how these HERVs affect brain cells to confer this increase in risk, our findings suggest that their expression regulation is important for brain function.’