Table 2 shows that eight of our twelve significant SNPs were located in DDC, and two were located in COMT. To examine whether these SNPs could be expected to explain unique variance in sensation seeking, we estimated the intercorrelations among all significant SNPs located within a single gene. In our sample, the two COMT SNPs (rs174699 and rs933271) had an r-squared value of 0.03, suggesting that linkage disequilibrium (LD, i.e., correlation between SNPs) was not responsible for the significant association of both with sensation seeking. Among the eight DDC SNPs significantly associated with sensation seeking, three (rs11575522, rs11575542, and rs11575543) were highly intercorrelated (r2 = 0.95–0.98). Nevertheless, even including these highly intercorrelated SNPs, the median r-squared value among the significant DDC SNPs was 0.04, indicating that linkage disequilibrium was likely not driving the inclusion of a relatively large number of DDC SNPs in our aggregate score.
