Social Environmental Effects On Externalizing Behavior: Moderating Effects On GABRA2

Introduction. Alcohol use among youth remains a public health concern. Trends suggest high rates of use, decreased average age of initiation and large economic costs for underage drinking (NRC, 2004).  Yet, prevention programs have not demonstrated large-scale success (Ennett et al., 1993). A greater understanding of developmental precursors to alcohol use (e.g., externalizing problems), including biological and social contexts, may enhance prevention efforts.

Genetic variants in candidate genes such as GABRA2 are associated with adult alcohol dependence (Edenberg et al., 2004) and externalizing trajectories (Dick et al., 2009). Yet, few biological processes operate independently of social context (Galea et al., 2004), leading to explorations of genetic and environmental interactions. The peer group is a primary social context for youth and deviant peer affiliation significantly predicts problem behaviors (Haynie & Osgood, 2005). Gene x peer delinquency interactions are investigated with regard to externalizing behavior and a component of that domain, rule-breaking, using GABRA2 SNP rs279826 as the genetic effect. We hypothesized that youth with a genetic risk for alcoholism (G, minor allele) would exhibit greater rule-breaking when exposed to deviant peers. 

Methods. The sample consisted of 244 adolescents in the Michigan Longitudinal Study (30.5% female, 95.1% White) genotyped for GABRA2 SNP rs279826 with available (perceived) peer delinquent involvement and problem behavior data. Peer delinquency was assessed at Wave 4 (ages 12-14) using the peer delinquency component of the Peer Behavior Profile.  Externalizing behavior and rule-breaking (i.e., delinquency subscale) at Wave 5 (ages 15-17) were assessed using the Teacher Report Form (Achenbach & Rescorla, 2001). Separate multilevel linear regression models were estimated for rule-breaking and externalizing with sex and race as covariates.

Results. Peer delinquency moderated the influence of GABRA2 on rule-breaking (p < .05). Specifically, the GABRA2 GG genotype predicted increased rule-breaking among adolescents endorsing high (t = 2.80, p < .01), but not low levels of delinquent involvement.  Perceived peer delinquency also moderated the influence of GABRA2 on externalizing behavior (p <.05). The GABRA2 GG genotype predicted higher externalizing behavior among adolescents endorsing high (t = 2.58, p< .01), but not low delinquent involvement.

Conclusions. Findings provide support for continued research on the role of peer delinquency as a moderator of genetic effects whereby the effect of GABRA2 on problem behavior varies as a function of delinquent involvement. Understanding how social contexts moderate genetic risk for alcoholism has the potential for informing preventive interventions.