DNA was isolated from the blood of each participant using a DNA Maxi kit from Qiagen, Inc. (Valencia, CA). A total of 22 SNPs, with 7 from CHRNA5, 11 from CHRNA3, and 4 from CHRNB4, were selected from either published papers (Berrettini and others 2008; Saccone and others 2007) or the NCBI SNP database (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=snp) on the basis of the potential biological functions of the gene, high heterozygosity with a minor allele frequency (MAF) > 0.15, and association analysis results from other studies (Berrettini and others 2008; Saccone and others 2007), as well as an attempt to obtain uniform coverage of the gene/region. Detailed information about these SNPs (alleles, physical position, allele frequency, and primer/probe information from ABI) is summarized in Table 1.
