Abstract:

The majority of studies on the gene by environment interaction have focused on family factors and stressful life events as environments, while research including peer contexts as environmental factors is rare. However, whether and how peer environments interact with gene on adolescent depression are less well understood, especially during early adolescence, a crucial period for examining the role of peer experiences in psychosocial adjustment. Peer victimization experience may result in negative self-evaluations, and in turn lead to anxiety and depression. However, the genetic makeup involved in the dopaminergic pathway could determine the degree to which a person is influenced by the peer environment. In this study, one of the most widely studied functional polymorphism (TaqIA) in the dopamine receptor D2 (DRD2) gene was used to test whether DRD2 gene moderates the effect of peer victimization on depression. Despite the extensive evidence supporting DRD2 by environment interaction on depression, the actual patterns of gender differences observed are inconsistent across studies. It also remains unknown whether gender moderates the way that TaqIA polymorphism interacts with peer environments. One thousand and sixty three adolescents of grade 6 (mean age 12.32 ± 0.49 years old at the first time point) from 40 classes of 14 primary schools in Jinan were assessed twice with an interval of two years. During each assessment, the participants completed self-reported questionnaires on experience of peer victimization and on depressive symptoms. All measures showed good reliability. DNA was extracted from saliva. Genotyping at TaqIA polymorphism in the DRD2 gene was performed for each participant in real time with MassARRAY RT software version 3.0.0.4 and analyzed using the MassARRAY Typer software version 3.4 (Sequenom). To examine whether TaqIA polymorphism moderates the effects of peer victimizations on adolescent depressive symptoms and whether this potential moderating effect differs between boys and girls, hierarchical regression analyses were conducted on males and females separately. Scores on physical and relational victimization and depressive symptoms were square-root transformed to eliminate skew before analysis. We also tested above questions by recoding peer victimizations into categorical variables (individuals had never experienced any victimization vs. individuals had experienced victimization) and conducted ANOVA analyses within each gender. The findings indicated that the two forms of victimization (physical and relational victimization) had no main effect on later depressive symptoms after controlling for social economic status and previous depressive symptoms. No main effect of DRD2 on depressive symptoms was found. The TaqIA polymorphism interacted with both forms of peer victimization in predicting male adolescent depression at age 14. Specifically, male adolescents with A2A2 genotype exhibited higher levels of depression when encountered with peer physical and relational victimization, compared to their counterparts with at least one A1 allele. However, such an interactive effect was not observed among females. In addition, the results of analyses of ANOVA replicated the associations among TaqIA polymorphism, peer victimizations and early adolescent depressive symptoms. These findings highlight the importance of investigating the moderating effect of peer context in the association between gene and depressive symptoms, especially during early adolescence. Besides, the associations among TaqIA genotype, peer physical and relational victimization and depressive symptoms in community populations differ substantially by gender.

Key words: DRD2 gene TaqIA polymorphism, peer victimization, depression, gender difference