The genome-wide significant SNP for Conscientiousness (rs2576037) is located in an intron of the KATNAL2 gene on chromosome 18q21.1 (P = 4.9 × 10−8, explained variance 0.21%.). The second-most significant SNP for Conscientiousness (rs7233515) is a non-synonymous SNP in the same gene (lowest P = 7.9 × 10−8, the r-squared with rs2576037 ranges between 0.92 and 1 across studies, Figure 1b). Variation in this SNP leads to a N88S amino acid change, suggesting a biologically relevant variation. In eight studies the direction of the effect for rs2576037 was the same (Figure 2b). In spite of this, there was nominal significant heterogeneity in the regression coefficients across studies (χ2 = 17.98, df = 9, P = 0.04). To test which study caused the observed heterogeneity, we reran the meta-analysis multiple times, by each time excluding one of the individual studies. Two studies seemed to account for the heterogeneity. Excluding the Finnish HBCS study (with the largest effect), heterogeneity was no longer significant (χ2 = 11.30, df = 8, P = 0.19) and the pooled p-value became 4.3 × 10−6. When excluding
