title: Educational attainment, smoking initiation and lifetime nicotine dependence among male Vietnam-era twins.
abstract: BACKGROUND
  Smoking initiation and persistence are clearly associated with factors commonly thought to be environmental in origin, including socio-economic status. However, twin models that incorporate gene-environment correlation and gene x environment interaction have not been applied to elucidate the genetic or environmental role that socio-economic status plays in smoking initiation and nicotine dependence.
  
  
  METHODS
  Twin structural equation modelling was used to examine gene-environment correlation and gene x environment interaction of one index of socio-economic status, educational attainment, with smoking initiation and nicotine dependence among 5119 monozygotic and 4295 dizygotic male-male Vietnam-era twins from the Vietnam Era Twin Registry, a national registry of twin pairs who served in the military during the Vietnam era.
  
  
  RESULTS
  Educational attainment correlated significantly with smoking initiation (r=-0.27, p<0.001). Additive genetic (p=0.011), shared environment (p=0.002) and unique environment (p=0.027) components contributed to the correlation between educational attainment and smoking initiation. Educational attainment also significantly moderated the variance in smoking initiation (p<0.001), suggestive of gene x environment interaction, although the interaction with the additive genetic, shared environmental and unique environmental components could not be resolved due to multi-collinearity. In contrast, educational attainment neither correlated with nor moderated nicotine dependence, once smokers had initiated.
  
  
  CONCLUSIONS
  Our study suggests that educational attainment is associated with smoking initiation, in part due to gene-environment correlation and gene x environment interaction. However, once smoking initiation is taken into account, there are no effects--be they gene-environment correlation or gene x environmental interaction--of educational attainment on nicotine dependence.
authors.affiliation: Centers for Behavioral and Preventive Medicine, Brown Medical School and The Miriam Hospital, Providence, RI 02903, USA. Jeanne_McCaffery@brown.edu
authors.forename: J M
authors.initials: JM
authors.lastname: McCaffery
authors.forename: G D
authors.initials: GD
authors.lastname: Papandonatos
authors.forename: M J
authors.initials: MJ
authors.lastname: Lyons
authors.forename: K C
authors.initials: KC
authors.lastname: Koenen
authors.forename: M T
authors.initials: MT
authors.lastname: Tsuang
authors.forename: R
authors.initials: R
authors.lastname: Niaura
mesh_terms: D000328:Adult; D015331:Cohort Studies; D004200:Diseases in Twins / Q000453:epidemiology / Q000523:psychology; D004522:Educational Status; D020022:Genetic Predisposition to Disease / Q000453:epidemiology* / Q000523:psychology*; D006801:Humans; D008297:Male; D012042:Registries; D012907:Smoking / Q000523:psychology*; D012931:Social Environment; D012959:Socioeconomic Factors; D013997:Time Factors; D014029:Tobacco Use Disorder / Q000453:epidemiology* / Q000523:psychology*; D014481:United States / Q000453:epidemiology; D047829:Vietnam Conflict