From twin and family studies we know that heritability estimates for both neuroticism and extraversion are moderate, with no major differences in estimates between the two dimensions. In the current design, however, we observe a larger estimate of variance explained for extraversion compared with neuroticism. A possible explanation for this discrepancy is that the phenotypic and biological complexity underlying neuroticism, is greater than for extraversion, causing diluted associations between genetic polymorphisms and neuroticism.65 The personality dimension of neuroticism includes facets related to both anxiety and depression, which although genetically correlated.66 may imply multiple biological dimensions. Other explanations for the lower estimate of variance explained by SNPs for neuroticism compared with extraversion may reflect differential impact of some of the reasons listed above. However, all explanations are speculative as yet.
