A total of 1,249 unrelated European-Americans (EAs) and 1,790 unrelated African-Americans (AAs) were genotyped and included in analysis. The number of included subjects across the five recruiting sites are 1233, 1226, 310, 249 and 21 for UConn, Yale, MUSC, UPENN and McLean, respectively. Subjects were considered “affected” based on smoking behavior as defined by a DSM-IV diagnosis of ND and the Fagerstrom Test of ND (FTND). Lifetime, as opposed to current, measures were considered. Cigarettes smoked per day (CPD) was also tested for genetic association as a quantitative trait. Never-smokers are included in the current study. The diagnosis of DSM-IV ND was made using a computerized algorithm that applied the DSM-IV diagnostic criteria for the disorder (American Psychiatric Association, 1994). The FTND score (Heatherton et al., 1991) (range 0–10) was derived from the SSADDA, in which the FTND questions were embedded. Based on prior work (Saccone et al., 2009b), we dichotomized FTND scores as follows: and FTND score ≥4 was defined as a “case”, an FTND score ≤1 was defined as a “control,” and subjects with scores in-between those values
