All individuals (N = 2772) were recruited by the Collaborative Genetic Study of Nicotine Dependence (COGEND), a United States multi-site project. All cases and controls reported smoking ≥100 cigarettes lifetime, the threshold classically used to define a smoker [26]. In recruitment of new subjects, cases were nicotine dependent, defined by current FTND≥4, and controls were required to have lifetime FTND of 0 or 1. The AA genetic sample in COGEND consists of 461 cases and 249controls. The EA genetic sample of 1063cases and 999 controls consists of 454 new subjects (266 cases, 188 controls) together with 1608 original COGEND EA individuals previously analyzed in [9, 10] (797cases (FTND≥4), 811 controls (FTND=0)).
