Dopamine-related genes were identified from a search of the relevant candidate-gene literature. Only genes located on autosomal (i.e. non-sex) chromosomes that have definite and direct effects on the dopaminergic system were included. SNPs in each of these genes (identified from dbSNP; Database of Single Nucleotide Polymorphisms, build 129) that were available on the Illumina Human 1M Bead Chip were then selected. Functionality of each SNP was identified using dbSNP. A total of 273 SNPs were chosen for inclusion in our analyses. Table 1 reports the genes included in our analyses, the number of SNPs available in each gene from the SAGE genotype data, and the general function of each gene as it relates to dopamine. (Note. No SNPs from the DRD5 gene were included in our analysis, because the single SNP available in this gene on the Illumina 1M platform did not pass genotyping quality control procedures in the SAGE sample. In addition, our sample did not include genotyping of rs1800955, or a reasonable proxy, a SNP in DRD4 showing significant association with impulsivity-related personality traits in a recent meta-analysis by Munafò and colleagues, 2008.)
