Saliva samples (~2 mL) were collected in an Oragene OG-500 DNA kit (DNA Genotek, Ottawa, ON). DNA was extracted per manufacturer’s instructions. The OPRM1 A118G variant (rs1799971) was genotyped using the C___8950074_1_ TaqMan pre-designed assay (LifeTechnologies, Burlington, ON). For each reaction, 20 ng genomic DNA were amplified as per manufacturer’s directions scaled to a total volume of 10 µL in an Applied Biosystems (AB) 2720 thermal cycler. Post-amplification products were analyzed on the ViiA™ 7 Real-Time PCR System. Genotype calls were determined manually by comparison to six No Template Controls. Genotyping of 10% of samples from each run were replicated for quality control. DNA was unavailable for two participants, leaving a sample of 38 participants for analyses involving OPRM1. Genotype frequencies did not diverge from expected distributions under Hardy-Weinberg equilibrium (AA = 28, GA = 9, GG = 1, (χ2[1]= 0.07, p = 0.79). The GG participant was grouped with GA participants to compare 118G carriers to 118A homozygotes. Genotype groups did not differ significantly by sex, race, or substance use (Table 1).
