The Collaborative Genetic Study of Nicotine Dependence (COGEND) is a multi-center case-control study designed to identify genes that contribute to nicotine dependence (Saccone et al., 2007). Community based recruitment enrolled participants ages 25–45 years old. Cases were required to be current smokers and have an FTND score of 4 or more. Controls were required to have smoked at least 100 cigarettes and have a lifetime maximum FTND score of 0 or 1. For this analysis, only subjects who self-reported as being of European ancestry were examined (previous analyses using EIGENSTRAT have shown a high correspondence with genetic ancestry groups; Saccone et al., 2009). Genotyping of variants to calculate the metabolism metric in COGEND has been previously described (Bloom et al., 2012). We focused on the subsample of 377 COGEND young adults ages 25–30 that overlapped with the ages of the primary COGA sample. From this group, 335 (89%) reported smoking every day or nearly every day for at least 2 months and were considered daily smokers. Replication sample characteristics of these daily smokers are described in Table 1.
