The genetic epidemiology of irrational fears and phobias in men

Background: Much of our knowledge of the role of genetic factors in the eti ology of phobias comes from one population-based sample of female twins. We examined the sources of individual differences in the risks for phobias an d their associated irrational fears in male twins. Methods: In personal interviews with bo th members of 1198 male-male twin p airs (707 monozygotic [MZ] and 491 dizygotic [DZ]) ascertained from a popul ation-based registry, we assessed the lifetime history of agoraphobia and s ocial, animal, situational, and blood/injury phobias as well as their assoc iated irrational fears. Twin resemblance was assessed by means of probandwi se concordance, odds ratios, tetrachoric correlations, and univariate and m ultivariate biometrical model fitting. Results: The suggestive results obtained by analysis of phobias only were s upported by analyzing both fears and phobias. All 5 phobia subtypes aggrega te within twin-pairs. This aggregation is due largely or solely to genetic factors with heritability of liabilities ranging from 25% to 37%. Multivari ate analysis revealed a common genetic factor, genetic factors specific to each subtype, and a common familial-environmental factor. Conclusions: In male subjects, genetic risk factors. which are partially co mmon across all subtypes and partially subtype specific, play a moderate ro le in the etiology of phobias and their associated irrational fears, Family environment probably has an impact on risk for agoraphobia and social phob ia. The genetic liability to blood/injury phobias is not distinct from thos e of the more typical phobias.