The interactions of dopamine D4 receptor and family cohesion or conflict on university students' prosocial tendency

Dopamine D4 receptor (DRD4) has been proved to be closely related to human social behavior. In particular, many studies have found that it interacts with family environment on prosocial behavior. However, there are some critical imperfection in current researches: 1) Most of the related researches focus on DRD4 7 repeat allele (DRD4-7R), while in fact there are great racial differences in the variable number of tandem repeats (VNTR) polymorphism of DRD4. In Asian population, the highest frequency of allele is DRD4 4 repeat allele (DRD4-4R). 2) There are three models to explain the interaction between DRD4 polymorphism and environmental factors on social behavior: diathesis-stress model, differential susceptibility model and vantage sensitivity model. The latter two models are supported by more evidences, but show inconsistent conclusions. 3) The main analysis method of the above interaction is hierarchical regression, which is simple and easy, however, with noticeable disadvantages. This method only focuses on the two ends of environment variables, and does not set quantitative standards for the size of interaction effects. To solve this problem, Roisman et al. proposed the region of significance (RoS) method, and Widaman et al. proposed a re-parameterized regression model. 4) Since gender is the influencing factor of the relationship between DRD4 and social behavior, in the interaction between DRD4 and family factors on social behavior, does gender effect still exist? If it does, is it a gender-contingent effect or a gender-specific effect? This study explored the interaction of DRD4 gene polymorphism and family cohesion or conflict on prosocial tendencies of university students, and analyzed whether the interaction fitted the differential susceptibility model or not, using RoS method and the re-parameterized regression model. Because of the similar function of DRD4-2R and DRD4-7R, the individuals carrying at least one DRD4-2R and the individuals carrying at least one DRD4-7R were combines as DRD4-2R (7R). Thus, there were two family sensitive gene types in this study: DRD4-2R(7R) and non-DRD4-4R. The findings indicated that: 1) For male university students, the interactions between DRD4-2R(7R) and family conflict on altruistic prosocial tendency, non-DRD4-4R and family cohesion on anonymous prosocial tendency, non-DRD4-4R and family conflict on altruistic prosocial tendency, and DRD4-3R(5R/6R) and family cohesion on anonymous prosocial tendency were significant. In other words, compared with non-carriers, family cohesion or conflict could significantly predict the prosocial tendency of male DRD4-2R(7R), non-DRD4-4R or DRD4-3R(5R/6R) carriers. Therefore, there was significant interaction between DRD4 gene polymorphism and family environment on prosocial tendencies of university students, and this interaction was gender-specific. 2) These four interactions fitted the differential susceptibility model whether through RoS method or the re-parameterized regression model. This study will be helpful to promote people's dynamic understanding of the prosocial development of the youth, and has some inspiration to improve the family education environment. Further research should pay attention to the longitudinal research design, the interaction of multiple genes and other environmental factors.