Virus That Infected Our Ancestors May Play a Role in Addiction

By Paul Gaita 09/28/18

Researchers studied whether the retrovirus played a part in promoting addiction in some individuals.

scientist holding a test tube

A virus that infected a human-related species more than 250,000 years ago may be the key as to why some individuals are more likely to develop dependencies towards drugs or alcohol.

A recent study found that traces of an ancient retrovirus—a virus that inserts its genetic code into its host's DNA—known as HK2 was 2.5 times more likely to be found in the genetic makeup of individuals who had contracted either HIV or hepatitis C through intravenous drug use than individuals who had become infected through other means, such as sexual intercourse.

Traces of the HK2 virus are believed to exist in approximately 5 to 10% of the global population.

The study—conducted by researchers from the University of Athens in Greece and Oxford University in London, England—was published in the journal Proceedings of the National Academy of Sciences and was comprised of two parts; the Greek research group analyzed the genes of more than 200 individuals with HIV, while the English group looked at the DNA of approximately 180 individuals infected with the hepatitis C virus. 

The Greek researchers found that the members of their study group that contracted HIV from intravenous (IV) drug use were 2.5 times more likely to have traces of the HK2 retrovirus in their genetic makeup than those who became infected through intercourse or other means.

The English researchers found similar results in their study group, with those who contracted hepatitis C through IV drug use and were long-time drug users 3.6 times more likely to have traces of the retrovirus in their genes than those who were infected in another manner.

As Live Science noted, when HK2 is found in an individual's DNA, it is found in a gene called RASGRF2, which is involved in the release of dopamine—the neurotransmitter linked to the brain's pleasure circuitry and the chemical released by the brain in large amounts during drug use which scientists believe causes the repetition of such experiences.

The second part of the study yielded less concrete results: scientists inserted traces of HK2 into the RASGRF2 gene in human cells that did not already contain it. While they discovered that the virus changed the means in which DNA created proteins, it remained unclear as to its direct connection to addictive behaviors.

According to co-senior study author Aris Katzourakis, professor of evolution and genomics at the University of Oxford, the study is "the first time that researchers have shown that an ancient viral insertion that's variably present in the population has a measurable, in this case detrimental, effect on our biology"—though as CNN noted, the RASGRF2 gene was associated with binge-drinking in a 2012 study.

The next step is to determine how HK2 influences dependent behaviors, with the end goal being a "drug to target" where the retrovirus has infiltrated the gene.

Doing that may allow science to "help people recovering from this kind of behavior," said Katzourakis.

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Paul Gaita lives in Los Angeles. He has contributed to the Los Angeles Times, Variety, LA Weekly, and The Los Angeles Beat, among many other publications and websites.