• Little is known about the role of familial and genetic factors in the etiology of generalized anxiety disorder (GAD), a new disorder first proposed in DSM-III. We examine this question in 1033 female-female twin pairs from a population-based registry. Both members in each twin pair were "blindly" assessed by structured psychiatric interview. Our results suggest the following: (1) GAD is a moderately familial disorder; (2) the tendency for GAD to run in families seems to be due largely or entirely to genetic factors shared between relatives rather than to the effects of the familial environment; (3) the heritability of GAD, estimated at around 30%, is modest, with the remainder of the variance in liability resulting from environmental factors not shared by adult twins; (4) the heritability of GAD cannot be explained solely by the occurrence of GAD only during episodes of major depression or panic disorder; and (5) the etiologic role of genetic factors is probably similar in GAD with a 1- vs a 6-month minimum duration of illness.
Kendler KS, Neale MC, Kessler RC, Heath AC, Eaves LJ. Generalized Anxiety Disorder in WomenA Population-Based Twin Study. Arch Gen Psychiatry. 1992;49(4):267-272. doi:10.1001/archpsyc.1992.01820040019002