Scientists: Risky Behavior Gene Predicts Marijuana Use

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Photo: Stephen Keable/Book of Odds

​A group of sociologists and geneticists trying to unravel the roots of human behavior heard from colleagues Saturday about research which indicates teenage boys who have two copies of a particular gene variant engage in fewer “risky behaviors” — including marijuana use — than their peers who carry at least one copy of another version of the same gene.

Interestingly, the “no-risk” gene appears to be greatly influenced by laws. Genetic protection against risky behaviors appeared only at ages when such acts were illegal, such as prior to age 21 for drinking alcohol, according to researcher Dr. Guang Guo of the University of North Carolina.


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University of North Carolina
Dr. Guang Guo led a team which concluded marijuana use and other “risky behavior” among young people is related to genetic structure

​Dr. Guo’s team analyzed data on 822 white males from a larger national sample, reports Bruce Bower at Science News. Participants were first interviewed in 1994, at ages 12 to 18. Follow-ups tracked the same participants for the next eight years.
Carriers of two copies of one common variant of the dopamine transporter gene showed generally lower rates of 10 “risky behaviors” than males with at least one copy of a different common version of that gene.
These self-reported behaviors included using marijuana, using cocaine, having multiple sex partners, binge drinking of alcohol, regularly smoking cigarettes, not wearing seat belts in cars, attacking others with weapons and other forms of delinquency.
Age — and law — played a big role in Guo’s findings. As boys reached ages at which alcohol and cigarette use became legal, the two genetic groups reportged using these substances at almost the same rates.
Thus the “risk gene” appears to avoid legal risk more avidly than it avoids physical risk, since obviously alcohol and tobacco are physically dangerous at any age.
A “protective” effect of the critical gene form appeared at all ages for marijuana and cocaine use, both of which remain illegal for recreational adult use throughout the United States.
Boys carrying the protective gene strapped on their seat belts while driving or riding in cars significantly more often than their non-protective gene carrying male peers did, beginning at ages 16 to 17, when they became legally able to drive.
Findings for all risky behaviors held after statistically accounting for participants’ physical maturity, verbal intelligence, popularity with peers, grade point average and church attendance, Guo reported.
Still, noted Kristen Springer of Rutgers University, it’s possible that carriers of the protective gene variant “mature out” of tendencies to engage in risky behaviors more quickly than their peers do, rather than relaxing when those acts became legal due to their ages.
Researchers said they need to replicate Guo’s provocative findings, a process than has proven elusive for previous gene/environment interaction studies, remarked Jeremy Freese of Northwestern University.
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