Individuals from the Collaborative Genetic Study of Nicotine Dependence (COGEND) used in these analyses were of European descent (N = 2,062). Recruitment of subjects started with community-based telephone-screening of approximately 50,000 people aged 25–44. The screening identified individuals who had smoked at least 100 cigarettes in their lifetime (smokers). The smokers then answered further questions about their smoking behavior, including the Fagerström Test for Nicotine Dependence (FTND) (Heatherton et al. 1991). This assessment identified nicotine dependent subjects who were current smokers with a score of 4 or higher on the FTND (cases). Non-dependent control subjects smoked at least 100 cigarettes, but were required to have a lifetime FTND score of 0 or 1 even during the heaviest period of smoking. Nicotine dependent cases and non-dependent controls who smoked were invited to participate in this genetic study of smoking. COGEND recruited subjects from three urban areas in the USA: St. Louis (N = 1,434), Detroit (N = 581), and Minneapolis (N = 47). The COGEND study was carried out with approval from the appropriate institutional review boards and with informed consent from all participants.
