The findings of the current study show that large-scale collaborative studies with combined sample sizes on the order of thousands or ten thousands still have difficulties in identifying common genetic variants that influence complex phenotypes such as personality traits. It could be that the effects of many SNPs are even smaller than the 0.2% that we were able to detect in this study at a genome-wide significance level. Larger GWA studies may reveal these variants, as has been already successfully demonstrated for human height in a large meta-analytic GWA study of over 180 000 individuals, in which at least 180 loci were identified together explaining about 10% of the variation in height.70 In addition, a recent paper using a novel technique to estimate the genetic variance explained by all SNPs, without focusing on genome-wide significance of individual SNPs, showed that common SNP variation explained about half of the heritability of human height.71 These papers are consistent with the notion that common SNP variation is important in explaining complex highly polygenic traits. It also suggests that the meta-analytic GWA study that we present here was only able to detect the top few SNPs with the largest effect sizes related to personality.
