Blood samples were collected for genetic analyses. Initial genotyping was performed by Perlegen Sciences using custom arrays as previously detailed and follow up genotyping was done by the Center for Inherited Disease Research (CIDR) using Illumina Golden Gate technology (14, 15, 30). For this study, we focused on two SNPs, rs16969968 and rs3743078 (a proxy for rs578776), located in CHRNA5 and CHRNA3 respectively.
