Aug. 7 (UPI) — Knowing that the genes of your high school friends may influence your risk of substance abuse and psychiatric disorders later in life may help you intervene before these problems arise, a new study finds.
The study, led by a researcher at Rutgers Robert Wood Johnson Medical School in New Brunswick, N.J., was published Wednesday in the American Journal of Psychiatry.
According to researchers, the genes of friends can have a domino effect on their peers, increasing the likelihood of drug and alcohol addiction, as well as serious depression and anxiety disorders in the long term.
“We found that the genetic makeup of peers, particularly peers who enter school later in adolescence, is associated with the risk of developing psychiatric and substance use disorders in young adulthood,” said Jessica Salvatore, lead author of the study.
Salvatore is an associate professor and director of the Genes, Environments and Neurodevelopment in Addictions program at Robert Wood Johnson Medical School.
“People who are genetically predisposed to these disorders are extra sensitive to the social genetic effects they experience from their peers,” she said.
Sociogenomics – the influence of one person’s genetic makeup on the observable traits of another – is an emerging field.
Other research has shown that the genetic makeup of peers can affect the health outcomes of their friends. To test this theory, Salvatore and her collaborators used Swedish national data to evaluate “social genetic peer effects” for several psychiatric disorders.
Researchers used a database of more than 1.5 million anonymous people born in Sweden between 1980 and 1998 to Swedish-born parents. They then mapped the individuals based on location and school during their teenage years.
They then consulted medical, pharmaceutical, and legal records that documented these people’s substance use and mental disorders in adulthood.
Researchers used computer models to assess whether the genetic makeup of peers predicted whether individuals would develop substance abuse, major depression and anxiety disorders in adulthood.
They classified the genetic predisposition of peers based on personalized measures of genetic risk, based on family history of the same conditions.
Even when researchers took into account variables such as people’s genetic predispositions and socioeconomic factors in the family, they found a clear link between the genetic susceptibility of their peers and the individuals’ likelihood of developing a substance abuse or psychiatric disorder. The effects were more pronounced among peers in school than among peers who lived geographically close to each other.
Within school groups, researchers observed the strongest effects among upper-secondary school classmates, particularly those who were in the same vocational or college-preparatory program between the ages of 16 and 19. These effects for school-age peers were more significant for drug and alcohol use disorders than for major depression and anxiety disorders.
According to Salvatore, more research should clarify why these correlations exist. He added that the findings are still compelling.
“When we think about genetic risk for a condition, we often think about how our own genes influence that risk,” she says.
“What the results of our study show is that the genetic makeup of social partners also matters. This should be considered as part of preventive intervention efforts.”
The research shows that parents have reason to be concerned if their teens are hanging out with the “wrong crowd” who come from families with drug and alcohol abuse or depression and anxiety, said Dr. Paul Appelbaum, a psychiatrist at Columbia University Irving Medical Center in New York City. He was not involved in the study.
“A distinction is usually made between genetic and environmental factors when it comes to influences on behavior,” said Appelbaum, whose research focuses on the ethical, legal and social implications of developments in genetics.
“This study is a creative attempt to illustrate that the effects of environment — in this case, the impact of one’s peers — can itself be linked to genetics. It suggests a much broader scope for genetic influences than is commonly appreciated.”
He noted that the conclusions remained the same even when the researchers looked at larger groups of peers: people who lived nearby and other students at school, especially those in the same major.
“That suggests that the broader environment in which someone lives has an impact, without even looking at someone’s immediate circle of friends,” Appelbaum said.
With this study, researchers have “brought us closer to the robust understanding that the genetics of a person’s social support system” can influence behavior, said Robbee Wedow, assistant professor of sociology and data science at Purdue University in West Lafayette, Indiana.
Their research “underscores the importance of the social networks one is part of, by uniquely linking the social and genetic components of behavior,” said Wedow, who is also an associate professor of medical and molecular genetics at the Indiana University School of Medicine in Indianapolis.
Still, it’s common and not surprising for friends to see similarities in their behavior, says David Ussery, a professor in the Department of Biomedical Informatics at the University of Arkansas for Medical Sciences in Little Rock.
“There is no reason to say that genes are responsible for this,” Ussery said, adding that “genes are like a piece of music: our health and our activities are the music, and it is very much dependent on the environment in which we live,” Ussery said.
“The ‘music of life’ is not played and controlled by our genes, but instead in the larger context of our cells and how they interact with each other, and influenced by our life history and events. It is not predetermined.”
Still, it’s surprising that a friend with a genetic predisposition to drinking could influence a peer to start drinking as well, even if the first person had not yet started drinking heavily at the time they met, says Alexander Urban, an associate professor of psychiatry, behavioral sciences and genetics at Stanford Medicine in Palo Alto, California.
“This was a somewhat unexpected result that requires further investigation,” Urban said.