Abstract

Background: Women report higher rates of major depression (MD) than men.Although genetic factors play an important etiologic role in MD, we are uncertain whether genetic factors are of equal importance in men and women, and whether the same genetic factors predispose men and women to MD. Methods:We obtained, by telephone interview, a lifetime history of MD, defined by the DSM-III-R, from 3790 complete male-male, female-female, and male-female twin pairs, identified through a population-based registry.Results were analyzed using probandwise concordance, odds ratios, and biometrical twin modeling. Results:The odds ratios (plus tetrachoric correlations) for lifetime MD were as follows: (1) male-male monozygotic, 3.29 (+0.37); (2) male-male dizygotic, 1.86 (+0.20); (3) female-female monozygotic, 3.02 (+0.39); (4) female-female dizygotic, 1.59 (+0.18); and (5) malefemale dizygotic, 1.39 (+0.11).In the best-fitting twin