2.2. Genotyping
As described in our previous report (Noohi et al., 2014), we collected participants’ saliva sample swith Oragene DNA self-collection kits.We identified the single nucleotide polymorphisms (SNPs) of COMT (rs4680), DRD2 (rs1076560), and BDNF (rs6265) genes for the provided DNA samples. Table1 presents that the distribution of alleles for each gene within the two age groups was in accordance with Hardy-Weinberg equilibrium. Taking the COMT-met, DRD2-G, and BDNF-val alleles as the “high performance” alleles, we defined a polygene index representing the Number of High Performance Alleles (NHPA) that each individual carries. As depicted in Table2, the total number of high performance alleles (i.e.NHPA score) can vary between 0 and 6. None of the subjects in our sample of young adults were carriers of 0 or 1 NHPA; only two older adult subjects were carriers of 0 (n=1) and 1(n=1) NHPA. To keep the consistency of comparisons across the two age groups, and to avoid the confounding effects of outliers, we did not include these two subjects in the final analyses.