'Fossil viruses' embedded in the human genome linked to psychiatric disorders

Ancient viral DNA embedded in the human genome may boost people's susceptibility to neuropsychiatric disorders, such as depression, bipolar disorder and schizophrenia.

A study published in May in the journal Nature Communications zoomed in on human endogenous retroviruses (HERVs) — snippets of DNA that form approximately 8% of the modern human genome.

Psychiatric disorders tend to run in families, and studies of twins have also hinted that genetics plays a role in whether people develop them. Estimates suggest that schizophrenia and bipolar disorder may have a heritability as high as 80%, meaning most of the variability seen in these disorders comes down to differences in people's genetics. 

Specific versions of genes, or gene variants, have been tied to these disorders, but not much is known about the iNFLuence of HERVs.

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"We were fascinated by the concept that [HERVs] existed in the human genome and so much was not known about them," study co-author Timothy Powell, a neuroscientist and molecular geneticist at King's College London, told Live Science.

HERVs are bits of viruses that have been woven into the human genome over evolutionary time, with the oldest examples introduced to our ancestors over 1.2 million years ago. Some HERVs are known to be switched on in cancer cells, and they may contribute to the disease; others are active in healthy tissues or play important roles in early development, so they're not necessarily all bad. Some HERVs are even active in the brain, but it's not yet clear what they're up to.