What is the genetic relationship between anxiety and depression?

Anxiety and depression share a long, close history in psychiatric nosology and treatment. The anxiety disorders, individually and as a group, exhibit remarkably high rates of comorbidity with each other and with major depression. Analyses done in large-scale epidemiologic surveys have identified major patterns of phenomenological overlap between these conditions. Researchers have tested hypotheses of shared genetic etiologies as a potential basis of this relationship. In general, available family studies have found mixed evidence for co-aggregation of anxiety and depressive disorders, while twin studies more definitively indicate that shared genetic risk factors largely account for this comorbidity. Some of this appears to be accounted for by genetic variation in personality traits that broadly predispose to anxiety and depression. Molecular genetic studies of these conditions, though too early to draw firm conclusions, thus far provide tentative support for specific genetic loci that may generally influence susceptibility across the anxiety-depressive spectrum.