Genetic contribution to the relationship between personality and depressive symptoms among older women.

BACKGROUND: Prior studies suggest that certain types of personality are at higher risk for developing depressive disorders. This study examined the relationship between old age depressive symptoms and two middle-age personality dimensions, neuroticism and extraversion. METHOD: The present study is part of the Finnish Twin Study on Aging, where altogether 409 female twins who had completed the Eysenck Personality Inventory at the age of 38-51 years were studied for depressive symptoms 28 years later using Center for the Epidemiologic Studies Depression Scale. Logistic regression analysis suitable for dependent data and univariate and Cholesky models for decomposing the genetic and environmental factor were used. RESULTS: Middle age extraversion protected from later depressive symptoms while neuroticism increased the risk. Twin modeling indicated that the association between neuroticism and depressive symptoms resulted from shared genetic risk factors common to both traits. However, a substantial proportion of the genetic vulnerability was specific to old age depressive symptoms and was not shared with neuroticism. Middle age extraversion had no genetic relationship with old age depressive symptoms. CONCLUSIONS: The relationship between middle age neuroticism and old age depressive symptoms is strong but only partly the result of genetic factors that predispose to both neuroticism and depressive symptoms. Extraversion, by contrast, has no genetic relationship with depressive symptoms experienced in old age.