The cause of anxiety disorders, including GAD, is unknown. However, there is evidence that anxiety disorders tend to run in families, suggesting that either genes or family environment (or both) may play a role in their development. There is some evidence to indicate that genes may play a modest role in GAD specifically. However, it is unlikely that anyone inherits an “anxiety” gene; instead, inheriting certain genes makes the development of GAD more likely to occur. Thus, you can inherit a predisposition to developing GAD, but if the right combination of environmental stresses does not occur in your life, you may never experience GAD.

Researchers are also investigating differences in brain function between people who have GAD and those who do not. Some evidence suggests that there may be differences in areas of the brain that control fear responses among the two groups. Researchers also believe that there may be differences in the brain chemistry of people with GAD. The levels of serotonin and norepinephrine, two chemical signals used in the brain (neurotransmitters), are different in people with anxiety disorders than in people without such disorders. While this research provides evidence that the brains of people with GAD may be working differently than the brains of other people, it does not tell us what causes this difference in the first place. It is most likely a combination of factors including genes and the stresses encountered in the environment.