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Ancient viral remnants persist in the human genome. Although their presence isn’t surprising to scientists, new research indicates that these viruses may influence the brain and contribute to contemporary psychiatric disorders.

Ancient viral DNA increases risk of psychiatric disorders

A team at King’s College London has found that ancient viral DNA in our genome increases the risk of conditions such as depression, schizophrenia, and bipolar disorder. According to their study in Nature Communications, about 8% of the human genome consists of Human Endogenous Retroviruses (HERVs). Once considered “junk DNA,” these viral fragments have now been shown to be expressed in the brain and to play a role in mental health issues.

The human genome comprises the entirety of genetic information found in almost all human cells, totaling around 20,000 to 25,000 genes. Genes are distinct DNA segments responsible for protein synthesis, essential for cell structure and function, organized in a predetermined sequence along the DNA molecule, creating a readable genetic code.

The human genome, comprising around three billion DNA base pairs, determines our physiological makeup, including inherited traits, physical attributes, disease susceptibilities, and certain behaviors.

Scientists from King’s College London’s Institute of Psychiatry, Psychology & Neuroscience (IoPPN) examined genetic data and conducted 800 brain autopsies to investigate the association between psychiatric disorders and the expression of HERVs in DNA.

Risk variations linked to psychiatric disorders impact genes

The majority of genetic risk variations associated with psychiatric disorders impact genes with established biological functions. However, researchers also discovered certain risk factors affecting the expression of ancient viral DNA in the brain. Five HERV expression signatures were identified, correlating with the onset of psychiatric disorders. Among these, two were associated with schizophrenia, one with both bipolar disorder and schizophrenia, and one specifically influenced the risk of depression.

Co-senior author Dr. Timothy Powell, the study utilizes a unique method to examine the impact of genetic vulnerability to psychiatric disorders on the expression of ancient viral sequences in the human genome. Findings indicate that these viral sequences likely have a significant influence on the human brain, particularly in relation to psychiatric disorder.