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The temporal relationship of the onsets of alcohol dependence and major depression: using a genetically informative study design

Published online by Cambridge University Press:  31 May 2006

PO-HSIU KUO
Affiliation:
Virginia Institute for Psychiatric and Behavioral Genetics, Department of Psychiatry, Virginia Commonwealth University, Richmond, VA, USA
CHARLES O. GARDNER
Affiliation:
Virginia Institute for Psychiatric and Behavioral Genetics, Department of Psychiatry, Virginia Commonwealth University, Richmond, VA, USA
KENNETH S. KENDLER
Affiliation:
Virginia Institute for Psychiatric and Behavioral Genetics, Department of Psychiatry, Virginia Commonwealth University, Richmond, VA, USA Department of Human Genetics, Virginia Commonwealth University, Richmond, VA, USA
CAROL A. PRESCOTT
Affiliation:
Department of Psychology, University of Southern California, Los Angeles, CA, USA

Abstract

Background. Although alcohol dependence (AD) and major depression (MD) are highly co-morbid, their causal relationship is unclear. In this longitudinal study, we used a genetically informative population-based twin sample to examine the age-at-onset distributions and the temporal relationship of AD and MD.

Method. Our sample included 7477 twins, whose diagnoses of AD and MD and age-at-onset information were obtained from structured interviews. Individual-level survival analyses were conducted based on 2603 monozygotic (MZ) twins, and co-twin diagnosis was included in models as an index of familiar liability to AD and MD.

Results. The age-at-onset distributions of AD and MD differed substantially. Most onsets of AD were in young adulthood, whereas MD had a flatter distribution across age. Most subjects, especially women, had an onset of MD preceding AD. Prior MD significantly affected risk for developing AD, and this risk decreased over time. By contrast, preceding AD had negligible effects on the risk for future MD. Familial risk was transmitted within disorders but there was little evidence of additional familial liability shared across disorders.

Conclusions. Risk for developing AD was substantially increased by a prior episode of MD. The association was only partially accounted for by familial factors, providing support for a direct causal effect such as self-medication. The etiologic path from AD to MD was insignificant.

Type
Original Article
Copyright
© 2006 Cambridge University Press

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