| According to the latest world health statistics report of WHO,mental disorders occur in all regions and cultures of the world.The most prevalent of these disorders are depression,which are estimated to affect nearly one in 10(676 million)people(WHO,2016).Adolescence is a crucial stage for the etiology of depression,with both the incidence rates of depression and levels of depressive symptoms increasing dramatically during this period(Avenevoli,Swendsen,He,Burstein,& Merikangas,2015;Hankin,2015).Depression is a highly prevalent disorder estimated to affect 8%~20% of adolescents globally before the age of 18(Naicker et al.,2013).The severity of depression reach the peak in mid-adolescence and close to adult depression(Natsuaki,Biehl,& Ge,2009;Twenge & Nolen-Hoeksema,2002).Thus,it is important to explore the etiology of depression.In the field of depression,accumulating research has documented that both gene and environment contribute to the development of depression.However,most of the extant studies have typically been conducted using a single polymorphism as the genetic risk index.It should be noted that the evidence that depression is highly polygenic has been ignored.In addition,the gene-brain/endphenotype-behavior framework has been raised for years,but a few studies has employed it or considered the role of environment in this process.Furthermore,most studies have investigated depression in adults,whereas few studies have focused on adolescence—one of the most important periods for onset of depression.Therefore,the current study aims to extend previous studies by employing a polygene design to examine the combined effect of multiple genes of dopaminergic systems and multiple peer environment factors,on adolescent depression and its underlying mechanisms.The specific research questions are:(1)how do polygene effects jointly impact the development of early adolescent depression(including analysis of multigene interactions and polygenic scores);(2)does adolescents’ temperament mediate the effect of polygene on early adolescent depression;(3)does peer experience moderated the indirect and direct effects of polygene on adolescent depressive symptoms;(4)does the A moderated mediation of multilevel peer experience contribute to a integration model.Participants with gene data were 1010 adolescents(Mage = 13.32 at T1,498 male)from The Dynamic Influence of Polygene and Environment on Early Adolescent Depression and the Mediation Mechanism hold by Prof.Zhang.Participants were originally recruited from Jinan Shandong Province when adolescence promoted to a junior middle school.Participants have completed 3 waves of data collection when adolescents were 13,14,15 years of age.Participants completed self-reported questionnaires on experience of peer victimization,temperament and on depressive symptoms.Peer nomination was used to measure adolescents’ peer rejection and acceptance.All measures showed good reliability.DNA was extracted from saliva.Genotyping at 4 locus(COMT Val158 Met,DAT1 rs27072,DRD2 Taq IA,DRD2 A241G)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).SPSS 21.0,R 3.2.2 and Mplus 7.0 were used to analyze the data.The main findings of this dissertation were as follows:1.In regarding to the polygenic effect on depression,this study showed that:(1)The levels of depressive symptoms increased with age.At 14 ~ 15 years of age,the growth rate slowed down.There was no gender difference on the level of depressive symptoms level significant gender differences.The prevalence of depression also increased,but the incidence rates of depression were less than 10%.(2)The dopamine genetic risk score was significantly associated with depression at three waves,with hingher genetic risk scores corresponding to greater levels of depression.This result lends support to the monoamine hypothesis.(3)There were no gender difference or age differences were found in the effect of polygene.2.In regarding to the polygenic effect on depression: the mediation of temperment,this study showed that:(1)The higher level of frustration and the higher level of fear were the risk factors of depression which supported motivational theories of depression.(2)Frustration mediated the association between dopamine genetic risk score and depressive symptoms,with greater polygenic score predict higher level of frustration,and in turn increased the risk of depression.(3)Frustration did not mediated the association between dopamine genetic risk score and depressive symptoms,suggested that the BAS plays a more important role than the BIS in affecting depression.3.In regarding to the moderated mediation model of the roles of polygenic risk score,frustration,and peer environment,this study showed that:(1)The main effects of polygenic risk score,peer acceptance/rejection,physical/relational victimization were significant.The peer acceptance was a protective factor of depression,whereas other peer experience were risk factors of depression.(2)The polygenic risk score interacted with relational victimization in predicting adolescent depression at age 15.Specifically,adolescents with higher polygenic risk score exhibited higher levels of depression when encountered with peer relational victimization,compared to their counterparts with lower polygenic risk score.The present result provides strong support for the diathesis-stress hypothesis.There were on significant interaction between polygenic risk score and other types of peer experience.(3)Peer acceptance were not moderated the indirect effects of polygenic risk score on adolescent depressive symptoms.(4)Peer rejection moderated the indirect effects of polygenic risk score on adolescent depressive symptoms,such that rejected adolescents with higher level of frustration were at an increased risk for depressive symptoms compared to non-rejected adolescents with higher level of frustration.The interaction was in consisted with diathesis-stress model.(5)Physical victimization were not moderated the indirect effects of polygenic risk score on adolescent depressive symptoms.(6)Relational victimization moderated the indirect effects of polygenic risk score on adolescent depressive symptoms,such that victimized adolescents with higher polygenic risk score were at an increased risk for higher level of frustration compared to non-victimized adolescents carrying higher polygenic risk score.The interaction was in consisted with diathesis-stress model.4.In regarding to the integration model,this study showed that:Peer rejection and relational victimization moderated the indirect effects of polygenic risk score on adolescent depressive symptoms.Peer rejection and relational victimization played different role in the mediation process.In addition,the direct effects of polygenic risk score on adolescent depressive symptoms were not moderated by peer experience.This study is expected to shed light on the polygenic underpinnings of adolescent depression,and the role of temperament as an underlying mechanism,as well as the complex moderated mediation among polygene,temperament and environments.In this way,the present study makes a novel contribution to the “gene-endphontype-behavior” framework.Furthermore,this study suggested that peer experience from different level play distinct roles in the polygenic process and also offer important implications for diagnosis,intervention and prevention of early adolescent depression. |
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