Given the findings described above, we hypothesize that affiliation with antisocial peers and CHRM2 genotypes are both likely to differentiate individuals displaying distinct trajectories of externalizing behavior across adolescence, with higher levels of peer group antisocial behavior and additional copies of the risk alleles resulting in increased risk of long-term behavioral problems. In addition, we hypothesize an interaction effect between these two factors in line with a diathesis-stress model of psychopathology, such that the influence of CHRM2 genotypes will increase among adolescents with more exposure to antisocial peers. As such, we will (1) identify discrete trajectories of adolescent externalizing behavior, (2) examine the predictive utility of a contemporaneous measure of antisocial behavior within the peer group and a set of nine correlated single nucleotide polymorphisms (SNPs) in CHRM2, and (3) test for gene-environment interactions between genetic variation in CHRM2 SNPs and peer group antisocial behavior.
