Mood disorders and personality traits are partly influenced by genetic risk factors. Heritability estimates are ∼40% for MDD, 50% for personality traits and between 60 and 90% for BD.10, 11, 12, 13, 14, 15, 16 This raises the question whether associations between personality and mood disorders are explained by shared genetic risk factors. So far, this has only been investigated for MDD. Twin studies have provided considerable support for overlapping genetic risk factors influencing N and MDD (reviewed in Middeldorp et al.17). Fewer twin studies have investigated the association with other personality traits and MDD suggesting a smaller, but significant genetic correlation between C and O and MDD,18 but not between E and MDD.19, 20, 21, 22
