Genomic DNA was collected from buccal cells (cheek swabs) following published procedures.33,34 For the brain samples, genomic DNA was extracted from 5 to 10 mg of the PFC using a commercially available product (DNeasy Mini Kit; Qiagen, Valencia, California) according to the manufacturer’s recommendations. The purity and quantity of DNA were determined by means of spectrophotometric analysis and then adjusted to a concentration of 20 ng/µL. The SNP rs2023239 was assayed using a premade TaqMan genotyping assay (hcv11600616; Applied Biosystems, Foster City, California). The SNP assays were performed using a reaction volume of 15 µL, which consisted of 7.5 µL of TaqMan 2X universal master mix (Applied Biosystems), 0.38 µL of 20X TaqMan predesigned SNP genotyping assay, 6.14 µL of nuclease-free water, and 1 µL of genomic DNA. After polymerase chain reaction amplification per the manufacturer’s recommendations, SNP genotypes were determined by allelic discrimination using a sequence detector instrument (ABI-7500; Applied Biosystems). At least 10% of the samples were repeated, and no error was detected when comparing those samples with the previous samples.
