In summary, a significant proportion of the phenotypic variance of neuroticism and extraversion can be explained by unknown causal variants in LD with common SNPs. This means that some of the so-called missing heritability of neuroticism and extraversion can be found in many common variants of small effects. The remaining discrepancy between our estimates from all the SNPs and the reported estimates of narrow sense heritability from pedigree studies might be attributed to (i) a large (er) role of rare variants, (ii) nonadditive effects (dominance and epistasis), and/or (iii) environmental influences that are included in the heritability estimate from pedigree studies but not in the heritability based on SNP data. Large samples with genome-wide sequencing data that are likely to become available with current developments in sequencing technologies may reveal the contribution of rare variants to the heritability of neuroticism and extraversion. Applying the current method to sequencing data could not only allow quantification of the contribution of rare variants, it should also be more conclusive about the total contribution of additive genetic effects to phenotypic variation in personality traits.
