Although both de Moor and Verweij failed to find genome-wide association to scales related to personality, there were key differences between these studies. They used different instruments to assess personality, and had very different sample sizes. One cannot rule out that the null results of de Moor et al.15 were due in part to the instrument used. While both the TCI and FFM dimensions are clearly heritable, at a similar magnitude, the locus-specific heritabilities of dimensions of both instruments are unknown and may differ. That is, if the proportion of variance in the TCI that is not accounted for by the FFM has higher locus-specific heritability than the FFM dimensions themselves, it is possible that the TCI will have greater success in genetic mapping. Although the GWAS of Verweij et al.18 used the TCI, the sample was not powered to detect genetic variants of small effect size (<1% of the variance explained). The aim of the current study was to employ meta-analytic techniques to evaluate the possibility of small genetic effects on the TCI. By combining four cohorts totaling over
