Friends' genetic traits may influence your behaviour

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by Dr Jenny Lange

The genetic predisposition for psychiatric and substance abuse disorders of a person's peer group may have long-term effects on their own risk of developing these disorders.

Sociogenomics is an emerging field that studies if a person's genetic makeup can affect the observable traits of another person. Using an anonymised database with information collected from 1.5 million people born in Sweden between 1980 and 1998 to Swedish parents, researchers used computer modelling to calculate genetic risk scores. They then assessed whether a person's genetic susceptibility could affect their peers' likelihood of experiencing depression, anxiety or substance abuse disorders themselves.

'We find that the genetic predispositions of peers, especially school-based peers in later adolescence, are associated with risk for developing psychiatric and substance use disorders in young adulthood,' Dr Jessica Salvatore, associate professor at the Rutgers Robert Wood Johnson Medical school, New Jersey, and lead author of the study, said.

In the study published in the American Journal of Psychiatry, the researchers mapped geographic and school location during teenage years, and referred to medical, pharmacy and legal registries to collect data on psychiatric conditions and substance abuse disorders. Peer family genetic risk scores appeared to increase the risk of a person developing the same condition; which was more pronounced for substance abuse disorders than major depressive disorder or anxiety. School environment had a greater impact than geographic location, and within school groups the strongest effects were observed in upper secondary school peers. People with a higher family genetic risk score appeared to be more susceptible to their peers' influence.

Family genetic risk scores were calculated based on the prevalence of these conditions within a person's relative circle. However due to the anonymised nature of the data cohort, no actual genetic information was collected and genetic predisposition could not be confirmed. While socioeconomic factors were accounted for, the lack of confirmed genetic risk variants within the cohort does not exclude social determinants in the family history of the psychiatric disorders studied.

'There's no reason to claim that genes are responsible for this... genes are like a musical score – our health and our activities are the music, and this is strongly dependent on the environment in which we live,' said Professor David Ussery from the University of Arkansas, who is not affiliated with the study. 'The "music of life" is played and controlled not 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 pre-determined.'

Due to the nature of the study, it does not address the complex interplay of genetics, epigenetics and social factors. More research is needed to gain an understanding of what drives the connections between peer genetic predisposition and psychiatric disorders, and confirm the long-term impact on health outcomes. This could have implications on health interventions and the need for these to be based within social networks.