Our results indicated that dopamine genes are associated with sensation seeking at the system level, that is, at the level of multiple SNPs in multiple dopamine genes. This systems approach had the ability to account for nontrivial variance; 3.9% (corresponding to a correlation of 0.20) of the variance in sensation seeking was explained using only 12 SNPs. Given a heritability of sensation seeking of 58.3% (Fulker & Eysenck, 1980), we were able to account for 6.6% of the heritable variance in sensation seeking. However, our sample was not of sufficient size to allow for cross-validation, and so this effect size estimate may be reduced when replication is attempted. Nevertheless, model fit indices demonstrated that significant independent variance was accounted for by the inclusion of multiple SNPs.
