All SNPs were genotyped in cocaine and opioid addicted subjects using Taqman® SNP Genotyping Assays (Applied Biosystems Inc. (ABI); Foster City, CA, USA). In a modification of the protocol recommended by manufacturers, we increased template DNA in the reaction from 2.5ng to 50ng. The standard Applied Biosystems protocol was otherwise followed. Quality control was maintained by genotyping 10% duplicates, which were checked for genotype concordance across the populations. The duplicate concordance rate for all 4 SNPs was 100%.
