Am J Psychiatry 1994; 151:1605-1614
Copyright © 1994 by American Psychiatric Association
Sources of individual differences in depressive symptoms: analysis of two samples of twins and their families
KS Kendler, EE Walters, KR Truett, AC Heath, MC Neale, NG Martin and LJ Eaves
Department of Psychiatry, Medical College of Virginia/Virginia Commonwealth University, Richmond 23298-0710.
OBJECTIVE: Self-reported symptoms of depression are commonly used in mental
health research to assess current psychiatric state, yet wide variation in
these symptoms among individuals has been found in both clinical and
epidemiologic populations. The authors sought to understand, from a
genetic-epidemiologic perspective, the sources of individual differences in
depressive symptoms. METHODS: Self-reported symptoms of depression were
assessed in two samples of twins and their spouses, parents, siblings, and
offspring: one sample contained volunteer twins recruited through the
American Association of Retired Persons and their relatives (N = 19,203
individuals) and the other contained twins from a population-based twin
registry in Virginia and their relatives (N = 11,242 individuals). Model
fitting by an iterative, diagonal, weighted least squares method was
applied to the 80 different family relationships in the extended
twin-family design. RESULTS: Independent analyses of the two samples
revealed that the level of depressive symptoms was modestly familial, and
familial resemblance could be explained solely by genetic factors and
spousal resemblance. The estimated heritability of depressive symptoms was
between 30% and 37%. There was no evidence that the liability to depressive
symptoms was environmentally transmitted from parents to offspring or was
influenced by environmental factors shared either generally among siblings
or specifically between twins. With correction for unreliability of
measurement, genetic factors accounted for half of the stable variance in
depressive symptoms. CONCLUSIONS: Depressive symptoms in adulthood partly
reflect enduring characteristics of temperament that are substantially
influenced by hereditary factors but little, or not at all, by shared
environmental experiences in the family of origin.
