Etiological heterogeneity of symptom dimensions of adolescent depression Jie Chen, 1 Jing Yu, 2 Leilei Zhang, 3 Xinying Li, 1 and Jianxin Zhang 1 1 Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, Beijing, China, 2 Department of Psychology, University of Maryland, Baltimore County, USA, 3 University of Chinese Academy of Sciences, Beijing, China Abstract: The aim was to investigate the underlying factor structure of adolescent depression and etiological heterogeneity in the symptom dimensions of adolescent depression. The sample included 842 pairs of same-sex adolescent twins, among which 613 pairs were monozygotic twins and 229 pairs were dizygotic twins. The ages of the participants ranged from 11 to 17 years (M = 13.64, SD = 1.80). Adolescents’ depressive symptoms were assessed using the self-reported Children’s Depression Inventory. Exploratory and confirmatory factor analyses were used to explore the factor structure of youth depression and twin genetic analyses were employed to estimate genetic and environmental influences on the derived dimensions. Results showed that adolescent depression encompassed five correlated dimen- sions: dysphoria mood, somatic symptoms, study and externalizing problems, anhedonia symptoms, and cognitive symptoms. These five symptom dimensions had heterogeneous etiologies: Dysphoria mood, somatic symptoms, and cognitive symptoms were moderately heritable (heritability ranged from 33 to 40%), whereas study and externalizing problems, and anhedonia symptoms were mainly environ- mentally influenced with minimal genetic basis. Our findings supported the multidimensionality of adolescent depression and the etiological heterogeneity of these symptom dimensions. Keywords: adolescent depression; etiological heterogeneity; genetic and environmental influences; multi-dimensionality Correspondence: Assistant Professor Jie Chen, 16 Lincui Road, Chaoyang District, Beijing 100101, China. Email: chenjie@psych.ac.cn Received 26 January 2014. Accepted 21 May 2014. Depression is a complex psychological disorder with an underlying heritable component (Belmaker & Agam, 2008). Family studies have identified a high familial tendency of depression and twin studies have demonstrated heritability estimates of 31–42% (Sullivan, Neale, & Kendler, 2000). However, there has been a lack of consistency in findings regarding the candidate genes associated with depression (Cohen-Woods, Craig, & McGuffin, 2013). Recent efforts to find new genes via genome-wide association studies using a case-control design have also largely been unsuccess- ful (Bosker et al., 2011; Kohli et al., 2011; Rietschel et al., 2010; Sullivan et al., 2008; Wray et al., 2012). In addition, one recent genome-wide association study com- prising 34,549 individuals found no loci significantly asso- ciated with continuous depressive symptoms (Hek et al., 2013). The heterogeneous nature of depression may, in part, con- tribute to these null or conflicting findings (Cohen-Woods et al., 2013; Flint & Kendler, 2014). Substantial evidence has supported the existence of subtypes of depression. For example, Sharpley and Bitsika (2013, 2014) suggested four clinical content subtypes of depression that supposedly pos- sessed different neurobiological pathways: depressed mood, anhedonic depression, somatic depression, and cognitive depression. Psychometric investigation of depression scales has also supported the multidimensionality of depression. For example, the factor analysis conducted by Quilty, Zhang, and Bagby (2010) supported the three-factor structure of the Beck Depression Inventory: affective, cognitive, and somatic depressive symptoms. Phenotypic heterogeneity indicates potentially distinct etiologies of the subtypes or symptom dimensions of depression. From the perspective of etiology, PsyCh Journal •• (2014): ••–•• DOI: 10.1002/pchj.62 © 2014 The Institute of Psychology, Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd