title: Developmental Changes in Genetic and Shared Environmental Contributions to Smoking Initiation and Subsequent Smoking Quantity in Adolescence and Young Adulthood.
abstract: BACKGROUND
  Few studies examining the genetic architecture of cigarette smoking have focused on adolescents or examined developmental changes in additive genetic, shared environment, and unique environmental influences on liability to initiate cigarette smoking and quantity of cigarettes smoked. The aim of this study was to add to the literature on liability to initiate and use cigarettes during adolescence using a nationally representative sample.
  
  
  METHODS
  Data for this study came from adolescent and young adult twin pairs (aged 14-33 years) from the National Longitudinal Study of Adolescent to Adult Health. We ran a series of developmental causal-contingent-common pathway models to examine whether additive genetic, shared, and unique environmental influences on liability to the initiation of cigarette use are shared with those on smoking quantity, and whether their contributions change across development.
  
  
  RESULTS
  We found evidence for a developmental shift in genetic and shared environmental contributions to cigarette use. Early in adolescence, genetic and environmental influences work independently on liability to cigarette smoking initiation and quantity of cigarettes smoked, but liability to these behaviors becomes correlated as individuals age into young adulthood.
  
  
  CONCLUSIONS
  These findings provide insight into the causal processes underlying the liability to smoke cigarettes. With age, there is greater overlap in the genetic and environmental factors that influence the initiation of cigarette smoking and quantity of cigarettes smoked.
authors.affiliation: School of Social Work,Virginia Commonwealth University,Richmond,VA,USA.
authors.forename: Cristina B
authors.initials: CB
authors.lastname: Bares
authors.affiliation: Department of Psychiatry,Virginia Commonwealth University,Richmond,VA,USA.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
authors.affiliation: Department of Psychiatry,Virginia Commonwealth University,Richmond,VA,USA.
authors.forename: Hermine H
authors.initials: HH
authors.lastname: Maes
mesh_terms: D000293:Adolescent; D000328:Adult; D004777:Environment; D005260:Female; D059647:Gene-Environment Interaction; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D012307:Risk Factors; D012907:Smoking / Q000235:genetics*; D055815:Young Adult
keywords: adolescents; cigarette smoking; development; environmental influences; genetic influences