Genotyping was conducted across 140.2 kb in the chromosome 4 region that contains GABRA2, and extending 63.1 kb 3′ towards the region where GABRG1 is located and 8 kb 5′. The intergenic region 3′GABRA2-5′GABRG1 was included based on previous literature showing association of SNPs in this region with AD (Covault et al., 2004; Covault et al., 2007). Twenty-six SNPs were selected from those already characterized in the literature as associated with AD and those identified in the region by the International HapMap Project (http://www.hapmap.org), which includes SNPs that have also been registered in The National Center for Biotechnology Information (NCBI) database (http://www.ncbi.nih.gov). Individual SNPs had to show a minor allele frequency > 0.05. Linkage disequilibrium (LD) between neighboring SNPs was taken into account by selecting SNPs that pair wise showed an r2 of <0.8. Table 1 lists the characteristics of the SNPs examined in the current study.
