Our model of aggregating multiple SNP effects from across genes within a single system is consistent with an additive model of genetic influence (the model of genetic influence employed for heritability estimates of sensation seeking; Fisher, 1918). The aggregation of multiple SNP effects into a genetic risk score is also well-aligned with current thinking on the nature of genetic influence on complex continuous traits. It is likely that numerous (e.g., thousands of) genetic polymorphisms, each with a small effect, contribute to the wide variation in observable human traits (e.g. Maher, 2008). The construction of theory-driven genetic risk scores (as in the candidate system approach demonstrated here) provides a promising direction for predicting phenotypic variation. Future work should focus on refining the genetic risk score, by using larger samples that would allow for greater accuracy in SNP selection and cross-validation.
