All subjects (789 cases and 811 controls) were selected from the Collaborative Genetic Study of Nicotine Dependence (COGEND), a US-based European ancestry sample (St Louis, Detroit, and Minneapolis). Details regarding recruitment and phenotypic assessments are in (Bierut et al., 2007; Saccone et al., 2007). Briefly, a personal interview was administered to assess nicotine dependence using the Fagerström Test for Nicotine Dependence (FTND) (Heatherton et al., 1991) and cases were defined by a current FTND score of 4 or more (maximum score of 10). Control subjects were defined as individuals who had smoked at least 100 cigarettes during their lifetime, yet never became dependent (lifetime FTND=0).
