Study participants were selected in the U.S. from a community-based sample participating in the Collaborative Genetic Study of Nicotine Dependence (COGEND) from sites in St. Louis, Detroit and Minneapolis. Participants who reported a lifetime smoking history of 100 or more cigarettes were included. The age range for eligible participants was 25–44 years. An initial telephone screen was used to determine nicotine dependence status based on the Fagerstrom Test for Nicotine Dependence (FTND) (Heatherton et al., 1991). Nicotine dependent cases were defined to have a current FTND scores ≥ 4, while non-nicotine dependent controls had a lifetime FTND scores of zero despite smoking more than 100 cigarettes lifetime. This control group was chosen in order to identify genetic determinants of nicotine dependence based on the original goal of the study. For further study details, see (Bierut et al., 2007; Saccone et al., 2007). The Institutional Review Boards at Washington University, University of Minnesota, and Henry Ford Health Sciences Center approved the protocols for this study. Blood samples collected for extraction of DNA were submitted along with electronic phenotypic and genetic data
