South Middlesex Times

A recent study led by a Rutgers Health professor has revealed that the genetic makeup of adolescent peers may have long-term consequences for individual risks of drug and alcohol use disorders, depression, and anxiety.

“Peers’ genetic predispositions for psychiatric and substance use disorders are associated with an individual's own risk of developing the same disorders in young adulthood,” said Jessica E. Salvatore, an associate professor of psychiatry at the Rutgers Robert Wood Johnson Medical School and lead author of the study published in the American Journal of Psychiatry. “What our data exemplifies is the long reach of social genetic effects,” Salvatore added.

Socio-genomics, which examines how one person’s genotype influences another's observable traits, is an emerging field. Research suggests that peers’ genetic makeup may influence health outcomes among friends. To explore this, Salvatore and colleagues used Swedish national data to assess peer social genetic effects for several psychiatric disorders.

The researchers utilized an anonymized database of over 1.5 million individuals born in Sweden between 1980 and 1998 to Swedish-born parents. They mapped individuals by location and school during their teenage years and then used medical, pharmacy, and legal registries documenting substance use and mental health disorders for these individuals in adulthood.

Models were run to determine whether peers’ genetic predispositions predicted target individuals’ likelihood of experiencing substance abuse, major depression, and anxiety disorder in adulthood. Peers’ genetic predispositions were indexed with family genetic risk scores—personalized measures based on family history—for the same conditions.

Even when controlling for factors such as target individuals’ own genetic predispositions and family socioeconomic factors, researchers found a clear association between peers’ genetic predispositions and target individuals’ likelihood of developing a substance use or psychiatric disorder. The effects were stronger among school-based peers than geographically defined peers.

Within school groups, the strongest effects were observed among upper secondary school classmates, particularly those in vocational or college-preparatory tracks between ages 16 and 19. Social genetic effects for school-based peers were greater for drug and alcohol use disorders than major depression and anxiety disorder.

Salvatore emphasized the need for further research to understand these connections fully.

“The most obvious explanation for why peers’ genetic predispositions might be associated with our own well-being is the idea our peers’ genetic predispositions influence their phenotype or the likelihood that peers are also affected by the disorder,” she said. “But in our analysis, we found that peers’ genetic predispositions were associated with target individuals’ likelihood of disorder even after we statistically controlled for whether peers were affected or unaffected.”

Salvatore highlighted what these findings mean for interventions:

“If we want to think about how to best address these socially costly disorders, we need to think more about network-based and social interventions,” she said. “It’s not enough to think about individual risk.”

This research underscores the importance of disrupting processes and risks extending at least a decade after school attendance. “Peer genetic influences have a very long reach,” Salvatore noted.

Coauthors include Henrik Ohlsson, Jan Sundquist, Kristina Sundquist from Lund University in Sweden; and Kenneth S. Kendler from the Virginia Institute for Psychiatric and Behavioral Genetics at Virginia Commonwealth University.