title: Defining nicotine dependence for genetic research: evidence from Australian twins.
abstract: BACKGROUND
  Whether current criteria used to define nicotine dependence are informative for genetic research is an important empirical question. The authors used items of the DSM-IV and of the Heaviness of Smoking Index to characterize the nicotine dependence phenotype and to identify salient symptoms in a genetically informative community sample of Australian young adult female and male twins.
  
  
  METHODS
  Phenotypic and genetic factor analyses were performed on nine dependence symptoms (the seven DSM-IV substance dependence criteria and the two Heaviness of Smoking Index (HSI) items derived from the Fagerström Tolerance Questionnaire, time to first cigarette in the morning and number of cigarettes smoked per day). Phenotypic and genetic analyses were restricted to ever smokers.
  
  
  RESULTS
  Phenotypic nicotine dependence symptom covariation was best captured by two factors with a similar pattern of factor loadings for women and men. In genetic factor analysis item covariation was best captured by two genetic but one shared environmental factor for both women and men; however, item factor loadings differed by gender. All nicotine dependence symptoms were substantially heritable, except for the DSM-IV criterion of 'giving up or reducing important activities in order to smoke', which was weakly familial.
  
  
  CONCLUSIONS
  The salient behavioral indices of nicotine dependence are similar for women and men. DSM-IV criteria of tolerance, withdrawal, and experiencing difficulty quitting and HSI items time to first cigarette in the morning and number of cigarettes smoked per day may represent the most highly heritable symptoms of nicotine dependence for both women and men.
authors.affiliation: Department of Psychiatry, Washington University School of Medicine, St Louis, MO, USA. Christina.lessov@sri.com
authors.forename: Christina N
authors.initials: CN
authors.lastname: Lessov
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Martin
authors.forename: Dixie J
authors.initials: DJ
authors.lastname: Statham
authors.forename: Alexandre A
authors.initials: AA
authors.lastname: Todorov
authors.forename: Wendy S
authors.initials: WS
authors.lastname: Slutske
authors.forename: Kathleen K
authors.initials: KK
authors.lastname: Bucholz
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Heath
authors.forename: Pamela A F
authors.initials: PA
authors.lastname: Madden
mesh_terms: D000328:Adult; D001315:Australia / Q000453:epidemiology; D039721:Diagnostic and Statistical Manual of Mental Disorders; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics*; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008297:Male; D010641:Phenotype; D015995:Prevalence; D012720:Severity of Illness Index; D014029:Tobacco Use Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*