Blood samples were collected for genetic analyses, and genotypic data were cleaned extensively (Bierut et al., 2007; Saccone et al., 2009; Saccone et al., 2007). We analyzed diplotypes using two distinct genetic variants in nicotinic receptor genes: rs16969968 and rs588765, which are located in the CHRNA5-CHRNA3-CHRNB4 nicotinic receptor subunit gene cluster on chromosome 15 and have previously been shown to be associated with nicotine dependence and function of CHRNA5 nicotinic receptor subunit (Saccone et al., 2009).
