Anxiety Disorders
Population Genetics
Family Studies
Family studies provide evidence that some anxiety disorders may be transmitted separately from one another. This is best established for panic disorder and least so for generalized anxiety disorder (GAD). Observations on the increased familial risk for anxiety disorders have been recorded in the literature for over 100 years. Family studies of panic disorder are often complicated by comorbidity with social phobia and GAD. One family study of pure panic disorder probands found a significantly higher risk for panic among first-degree relatives compared to relatives of controls. There was also a fivefold increase in risk for any anxiety disorder. Similarly, an increased risk for agoraphobia (11.6%) has been reported for the relatives of agoraphobic probands, compared to 1.9% for relatives of panic disorder probands and 1.5% for relatives of control probands. A study of simple phobia found an increased risk for simple phobia (31%) among relatives of probands with that diagnosis (but no other anxiety disorder) compared to relatives of control probands (11%). A family history study of social phobia demonstrated that relatives of phobic probands were at increased risk for this disorder (6.6%), compared to relatives of panic disorder probands (0.4%) or relatives of control probands (2.2%).
Distinctly separate genetic transmission is not well established for GAD. A family study found that relatives of GAD probands had a greater risk of GAD than relatives of control probands, but this risk was not greater than the risk for relatives of panic disorder probands. Conversely, a separate study reported similar risks for GAD among relatives of panic disorder probands and relatives of probands with GAD. Thus although some evidence suggests familial transmission of GAD, the transmission may not be specific.
Twin Studies
In a Norwegian sample, the concordance of all anxiety disorders for MZ twins (34.4%) was significantly greater than that for DZ twins (17.0%).
Linkage Studies
A study of 26 families with multiple cases of panic disorder included 77 persons with definite or probable panic disorder. Screening of the entire genome for linkage is now in progress in this and other samples. No definite linkage findings have been reported, but current interest centers on chromosome 7.
