Neuroticism is characterized by a tendency for emotional instability, psychological distress, low self-esteem and negative emotions such as anxiety and depression. Extraversion is characterized by a tendency for high levels of sociability, activity, sensation seeking and positive emotions. Both traits are predictive of a number of social and behavioural outcomes and of anxiety and depressive disorders.5, 6, 7, 8, 9 For example, high levels of neuroticism are associated with lifetime disorders such as major depressive disorder, generalised anxiety disorder, social phobia, dysthymia and obsessive-compulsive disorder. Low levels of extraversion are associated with social phobia, agoraphobia and dysthymia. Causes of individual differences in both neuroticism and extraversion have been studied extensively using twin and adoption studies, showing heritability estimates ranging from 13 to 58% for neuroticism and from 34 to 57% for extraversion.10, 11, 12, 13, 14, 15, 16, 17, 18 Genetic factors that are related to neuroticism and extraversion may also be genetic risk factors for associated mental disorders.7, 19, 20 Therefore, insight into the genetic architecture of neuroticism and extraversion may shed light on biological mechanisms underlying mental disorders that are associated with these traits.
