Comment; Fascinating!  A human DNA retrovirus that could be backloading genetic information that predisposes addiction into the genome of some people.  What are the predisposing factors/behaviors/genetics?  So much more to study!

By Kat Eschner September 24, 2018

Addiction is much more complex than a few bits of junk DNA—but that doesn’t mean they don’t play a part.

Millions of Americans struggle with substance abuse and tens of thousands die each year, according to the American Society of Addiction Medicine. Though treating addiction has become a vast (and at times abusive) industry, the underlying causes of drug or alcohol dependency—and how to successfully treat these debilitating conditions—are still poorly understood by science. Now, researchers think they’ve found the germ of an answer in our genetic past.

In this study, researchers from several institutions including Oxford University and the National-Kapodistrian University of Athens looked at an ancient retrovirus that’s present in the genes of only some humans, and found that HK2, the retrovirus, is present in people who use injection drugs in both Greece and Scotland at a higher rate than in the general population. They believe that their results offer evidence for a physical cause of addiction, although they don’t currently know the exact mechanism by which it works.

Human endogenous retroviruses are ancient retrovirus DNA that hangs around in our genes, passed from generation to generation as part of our genetic code. Mostly, they seem to just hang around as junk DNA, not doing much, but studies have posited a link between some HERVs and autoimmune disorders and other conditions, including some cancers. However, a formal link between a HERV and a human disease state has not been established. This research is a step toward demonstrating that an unusual HK2 integration present in just five to 10 percent of the population might actually contribute to addiction. In this integration, genetic information from the HK2 retrovirus is present in a gene involved in regulating your brain’s dopamine levels. Dopamine is a neurotransmitter that signals pleasure and reward in your brain—good feelings, when felt in small amounts, but associated with addiction when the brain becomes dependent on higher and higher levels provided by drug use.

To do their study, researchers first looked at two different groups of people who use injection drugs. Both groups had gotten a disease as a result of their injection drug use. In Greece, the cohort studied had been infected with HIV, and in Scotland, the cohort had been infected with Hepatitis C. The researchers used a basic genetic screening technique to analyze how many people had the rare HK2 integration. They also looked at people with the same infections who had contracted the diseases in other ways, and looked for the HK2 integration.

The drug users studied were between 2 and 3 times more likely than the control population to have the HK2 integration. Although there’s no proof of a causal relationship between HK2’s integration into the RASGRF2 gene and addiction, there is a “strong” correlation, says study author Gkikas Magiorkinis. They used the two populations, whose data can’t be compared, because “we wanted our study to be as robust as possible. The replication from two cohorts suggests that the finding is highly unlikely to be random,” he wrote in an email to Popular Science.

In future work, they hope to actually study the molecular mechanisms of action by which the presence of HK2 affects dopamine and demonstrate how the retrovirus DNA might influence drug abuse. But that won’t be simple work. How molecules provoke dopamine release has only recently been isolated in mice, who can be euthanized and studied during experiments. Studying the human brain in action requires less invasive measures, which makes it much more difficult. But “technologies like the functional MRI have made a real difference,” Magiorkinis says.


Dr. Raymond Oenbrink
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