title: A population-based twin study in women of smoking initiation and nicotine dependence.
abstract: BACKGROUND
  The development of drug dependence requires prior initiation. What is the relationship between the risk factors for initiation and dependence?
  
  
  METHODS
  Using smoking as a model addiction, we assessed smoking initiation (SI) and nicotine dependence (ND) by personal interview in 1898 female twins from the population-based Virginia Twin Registry. We developed a twin structural equation model that estimates the correlation between the liability to SI and the liability to ND, given SI.
  
  
  RESULTS
  The liabilities to SI and ND were substantially correlated but not identical. Heritable factors played an important aetiological role in SI and in ND. While the majority of genetic risk factors for ND were shared with SI, a distinct set of familial factors, which were probably partly genetic, solely influenced the risk for ND. SI was associated with low levels of education and religiosity, high levels of neuroticism and extroversion and a history of a wide range of psychiatric disorders. ND was associated with low levels of education, extroversion, mastery, and self-esteem, high levels of neuroticism and dependency and a history of mood and alcohol use disorders.
  
  
  CONCLUSIONS
  The aetiological factors that influence SI and ND, while overlapping, are not perfectly correlated. One set of genetic factors plays a significant aetiological role in both SI and ND, while another set of familial factors, probably in part genetic, solely influences ND. Some risk factors for SI and ND impact similarly on both stages, some act at only one stage and others impact differently and even in opposite directions at the two stages. The pathway to substance dependence is complex and involves multiple genetic and environmental risk factors.
authors.affiliation: Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Medical College of Virginia Commonwealth University, Richmond 23298-0126, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Kendler
authors.forename: M C
authors.initials: MC
authors.lastname: Neale
authors.forename: P
authors.initials: P
authors.lastname: Sullivan
authors.forename: L A
authors.initials: LA
authors.lastname: Corey
authors.forename: C O
authors.initials: CO
authors.lastname: Gardner
authors.forename: C A
authors.initials: CA
authors.lastname: Prescott
mesh_terms: D000328:Adult; D004777:Environment; D005260:Female; D006801:Humans; D011159:Population Surveillance; D012307:Risk Factors; D012907:Smoking; D013997:Time Factors; D014029:Tobacco Use Disorder / Q000175:diagnosis* / Q000235:genetics*; D014427:Twins / Q000235:genetics* / Q000523:psychology