title: Genetic and environmental influences on the association between depressive symptom dimensions and smoking initiation among Chinese adolescent twins.
abstract: BACKGROUND
  Extant twin research on the depression-smoking association in adolescents has been conducted in U.S. and European samples and considered depression as a unitary phenotype. This study explored genetic and environmental influences on covariation between smoking initiation and 4 depressive symptom dimensions (positive affect [PA], negative affect [NA], somatic features [SF], and interpersonal problems [IP]) in adolescent Chinese twins.
  
  
  METHODS
  Questionnaires measuring current depressive symptoms and lifetime smoking initiation were administered to 602 twin pairs (M [SD] age = 12.2 (1.93) years, range 9-16 years). Cholesky bivariate decomposition models examined influences on each depressive symptom dimension, smoking initiation, and their covariation using age- and sex-adjusted threshold variables.
  
  
  RESULTS
  Within-twin correlations between smoking initiation and each depressive symptom dimension were significant (|r|s = .29-.61). Bivariate twin modeling showed significant genetic effects on overall depressive symptoms (55% variance), shared environment effects on NA (36%) and PA (53%), and shared environment effects on smoking initiation (46%) unique from PA. No other familial influences on the individual phenotypes (apart from those accounting for smoking-depression covariance) were significant. Relations of smoking initiation to overall depressive symptoms and IP were influenced by familial (shared environment and/or genetic) factors and nonshared environmental factors. The SF-smoking initiation relation was influenced mostly by familial factors. Only shared environment significantly influenced the association of lower PA and higher NA to smoking initiation.
  
  
  CONCLUSIONS
  Relations between each symptom dimension and smoking initiation are of sizeable magnitude in Chinese adolescents. Genetic and environmental factors underlying depression-smoking comorbidity may vary across different depressive symptom dimensions.
authors.affiliation: Department of Preventive Medicine, University of Southern California Keck School of Medicine, Los Angeles, CA 90033, USA. adam.leventhal@usc.edu
authors.forename: Adam M
authors.initials: AM
authors.lastname: Leventhal
authors.forename: Lara A
authors.initials: LA
authors.lastname: Ray
authors.forename: Soo Hyun
authors.initials: SH
authors.lastname: Rhee
authors.forename: Jennifer B
authors.initials: JB
authors.lastname: Unger
mesh_terms: D000293:Adolescent; D002648:Child; D002681:China / Q000453:epidemiology; D003863:Depression / Q000453:epidemiology / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D012907:Smoking / Q000453:epidemiology / Q000523:psychology*