The addiction virus

The retrovirus turned out to be responsible for the propensity of people to drug addiction

Ksenia Murasheva, Naked Science

Retroviruses are RNA–containing viruses that trigger the synthesis of viral DNA in the cell. This happens as follows: after the virus enters the cell, it starts genome replication using the reverse transcription mechanism. One strand of DNA is synthesized on the viral RNA matrix, and then a second strand is completed on the matrix of this DNA, forming a full-fledged molecule. During cell division, when there is no nuclear envelope, the viral DNA is integrated into the DNA of the host cell. Only later, in a new cell, this section of DNA synthesizes new viral RNAs, which, when leaving the cell nucleus, are packed into protein shells and continue to infect new cells. A well–known representative of retroviruses is the human immunodeficiency virus (HIV). It differs from most other retroviruses in that its DNA can penetrate through the nuclear envelope.

In the human genome, there are many "remnants" of the DNA of retroviruses that invaded the cells of the germ line of our ancestors. Among such viruses is HERV-K HML-2 (HK2) – it can still spread in modern humans. Moreover, not everyone has the same retrovirus variants stored in the genome. One of these variants – a very specific HK2 – is located close to the genes responsible for the functioning of the dopaminergic system of the brain, specifically to the RASGRF2 gene. It turned out that such a variation of retroviral DNA is more common in people with drug addiction, from which doctors concluded that there was a certain connection.

Scientists from the University of Oxford and the University of Athens, testing the hypothesis, found that HK2 can indeed influence closely located genes and, thus, affect human behavior – in particular, addiction. They published their research in the journal Proceedings of the National Academy of Sciences.

Scientists analyzed samples obtained from patients diagnosed with hepatitis C (HCV virus) and HIV-infected patients who were infected specifically by injection. It is known that in about 5-10% of the human population, a specific variant of HK2 is embedded in DNA. In their sample, the researchers studied the frequency of such integration. It turned out that people with a pronounced tendency to addictions are two to three times more likely to integrate HK2 into the RASGRF2 gene, as we have already mentioned, which is responsible for dopaminergic brain activity.

Scientists believe that their study for the first time showed a link between the presence of retroviral DNA in the human genome and some complex features of its behavior. However, they recognize that many factors affect the development of addiction in a person.

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