SNPs chosen for genotyping included those in the neuronal nicotinic acetylcholine receptor genes CHRNA3, CHRNA4, CHRNA5, CHRNA6, CHRNB2, CHRNB3, and CHRNB4 with p<0.05 in a recent study of nicotine dependence (7, 8). Additional haplotype-tagging SNPs were chosen using the method of Gabriel et al. (16) and HapMap data available for Caucasians (CEPH) in July, 2006 (data release 21/phase II). SNPs which failed assay design were replaced by SNPs in high LD with the problematic SNPs. These selection criteria resulted in a total of 61 SNPs being chosen for genotyping. An additional 200 SNPs were selected and genotyped across the genome and used for the assessment of population stratification in these samples (17).
