Genomic DNA was collected and extracted from buccal cells using methods described previously.21 Assays for the DRD4 exon 3 VNTR and SLC6A3 9/10 repeat allele were conducted as described in22, with each DRD4 allele ≥ 7 repeats being considered a risk allele for the AGRS and each 9 repeat allele being a risk factor for SLC6A3. The COMT Val158Met and DRD2 TaqIA genotypes were obtained using the Taqman approach for rs4680 and rs1800497, respectively. Risk alleles for the AGRS were assigned as each copy of the Met COMT allele and each copy of the DRD2 TaqIA allele.
