A twin study of DSM-III-R anxiety disorders.

The prevalence of anxiety disorders was studied in a sample of 20 monozygotic (MZ) and 29 dizygotic (DZ) co-twins of anxiety disorder probands. A comparison group of co-twins of 12 MZ and 20 DZ twin probands with other non-psychotic mental disorders was also studied. All subjects were personally interviewed with the Structured Clinical Interview for DSM-III-R Axis I (SCID-I). Panic disorder was significantly more prevalent in co-twins of panic probands. Generalized anxiety disorder (GAD) was more prevalent in co-twins of GAD probands with a history of mood disorder (NS). Post-traumatic stress disorder was significantly more prevalent in co-twins of anxiety probands and was more prevalent in MZ than in DZ co-twins. The prevalences of social and simple phobia were equal in co-twins of anxiety and comparison probands. For both panic disorder and generalized anxiety disorder the MZ:DZ concordance ratio was more than 2:1. The results support the hypothesis of a genetic contribution in the etiology of panic disorder, generalized anxiety disorder and post-traumatic stress disorder. The hypothesis that simple and social phobia are mainly caused by environmental experiences was also supported.