Peer victimization and internalizing and externalizing problems among early adolescents: The longitudinal between × within moderation role of the FKBP5 gene.

Although many studies have demonstrated associations between peer victimization and internalizing and externalizing problems that may be moderated by genes, it remains unclear whether these links also apply to the within-person level. The present study investigated within-person associations between peer victimization and internalizing and externalizing problems, as well as the moderating effect of between-person differences in the FKBP5 gene. A total of 915 Chinese youth (43.9% girls; M _age = 10.34 years, SD = 0.94) participated in a three-wave longitudinal study with six-month intervals. A random intercept cross-lagged panel model was used to test the hypothesized moderation effects, enabling the examination of time-invariant moderators and the between × within interaction. Results revealed that peer victimization was bidirectionally associated with internalizing and externalizing problems at the within-person level. The FKBP5 gene moderated the within-person pathways from peer victimization to both internalizing and externalizing problems. These findings suggest that individuals with greater genetic susceptibility were more likely to develop internalizing and externalizing symptoms in response to peer victimization. These results highlight gene-environment interactions at the within-person level and underscore the importance of tailored interventions aimed at preventing internalizing and externalizing problems in adolescents.