The aggregate additive effect of all SNPs accounted for a little less than 30% of the variance in P3 amplitude and the genetic factor score, which is between 40% and 60% of the heritable variation in these measures. Approximately half the heritable variation thus appears to be due to common genetic variants. Nevertheless, we did not obtain any statistically significant associations between endophenotypes and individual SNPs, and the association with MYEF2, despite being genome-wide significant, has no precedent in the literature and awaits replication. Moreover, although the P3 genetic factor score, because it specifically reflects the additive genetic variance in P3 amplitude, would seem to be advantageous in GWAS, its usefulness consisted primarily in allowing us to assess the degree of correspondence between analysis results for the two endophenotypes.
