Familial aggregation of anxiety-related quantitative traits in generalized social phobia: clues to understanding "disorder" heritability?

Social phobia, particularly the generalized form, is strongly familial. Given the probable continuity from extremes of normative personality (e.g., shyness) to social phobia to personality disorder (e.g., avoidant personality disorder), it is unlikely that social phobia itself, at the level of an Axis I disorder, is transmitted. Rather, it seems more parsimonious, and in keeping with current notions about the structure and heritability of mental disorders, that one or more temperamental risk factors for social phobia is transmitted. The goal of this study was to explore this possibility by examining relevant quantitative traits in a family study of generalized social phobia (GSP). First-degree (n = 103) relatives of patients with DSM-IV GSP and 65 first-degree relatives of not socially phobic comparison subjects (NC) completed a panel of self-report questionnaires that included measures of trait anxiety, social anxiety, and personality. Regression analysis was used to examine associations between group membership (i.e., whether that family member was a first-degree relative of a GSP proband) and these measures. First-degree relatives of GSP probands scored significantly higher than first-degree relatives of not socially phobic probands on measures of trait anxiety and social anxiety and on the Harm Avoidance subscale of the TPQ. One large factor, accounting for 84% of the variance, was strongly associated with being a first-degree relative of a GSP proband. Quantitative traits elevated in probands with generalized social phobia are also elevated in their first-degree relatives. Future family and genetic studies of social phobia should consider the possibility that one or more traits (or some aggregation thereof) may better approximate the phenotype of interest. More extensive efforts at phenotype refinement should be undertaken before such studies proceed.