Defining nicotine dependence for genetic research: evidence from Australian twins

Background. Whether current criteria used to define nicotine dependence are informative for geneticresearch is an important empirical question. The authors used items of the DSM-IV and of theHeaviness of Smoking Index to characterize the nicotine dependence phenotype and to identifysalient symptoms in a genetically informative community sample of Australian young adult femaleand male twins.Method. 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 Fagerstro¨m Tolerance Questionnaire, time to first cigarette in the morningand number of cigarettes smoked per day). Phenotypic and genetic analyses were restricted to eversmokers.Results. Phenotypic nicotine dependence symptom covariation was best captured by two factorswith a similar pattern of factor loadings for women and men. In genetic factor analysis item covariationwas best captured by two genetic but one shared environmental factor for both womenand men; however, item factor loadings differed by gender. All nicotine dependence symptomswere substantially heritable, except for the DSM-IV criterion of ‘ giving up or reducing importantactivities 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 timeto first cigarette in the morning and number of cigarettes smoked per day may represent the mosthighly heritable symptoms of nicotine dependence for both women and men