All subjects (1032 cases and 995 controls) were selected from the Collaborative Genetic Study of Nicotine Dependence (COGEND), a US-based community sample aged 25–44 years of age from Detroit and St. Louis, recruited through telephone screening. The Institutional Review Board approved the study and all subjects provided informed consent to participate. Blood samples were collected from each subject for DNA analysis and submitted together with electronic phenotypic data to the NIDA Center for Genetic Studies (http://www.nidagenetics.org/). All subjects self-identified as being of European descent (30). See Table 1 for the sample characteristics.
