Genetic Underpinnings - What Causes Anxiety: Anxiety Disorder

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Genetic underpinnings

People with a parent or sibling who has had an anxiety disorder are at greater risk of developing one. For many years, experts debated whether this link was due to nature (a genetic predisposition that's passed from one generation to the next) or nurture (anxiety-provoking behaviors that are learned in families or are caused by stressful experiences growing up). It's now clear that these factors often interact.

Still, much is unknown, and the genetic factors are hardly straightforward. Researchers studying families with a history of anxiety disorders have scrutinized their genetic makeup in hopes of finding common features. Several candidates have been identified. Some are variants of genes, while others are regions on chromosomes that seem similar. But none of these genetic traits appears uniformly in people with anxiety disorders. Therefore it's unlikely that there's any single "anxiety gene." Many genes probably work together to induce the disorder.

One anxiety gene uncovered

So far, scientists have identified one anxiety-related gene in humans. This gene, called 5-HTT, regulates serotonin, a neurotransmitter that affects mood. A variation of this gene speeds the metabolism of serotonin by neurons (nerve cells), leaving less of the chemical available in the brain. Low levels of serotonin seem to be characteristic of anxiety disorders, depression, and other mental health disorders. One study found that this genetic variation was more than three times more common in people with generalized anxiety disorder than in people who did not have the disorder. It was also more prevalent in people with obsessive-compulsive disorder.

In a 2000 study in the Journal of Abnormal Psychology, researchers took blood samples from 72 people to see who had the 5-HTT gene variation. The participants then breathed a carbon dioxide–oxygen mix that causes shortness of breath, a sensation that sometimes provokes fearfulness and anxiety. The test provoked fear only among those with the genetic variation. It's important to note that none of the participants — even those with the gene variant — had symptoms of anxiety disorders before the experiment. Thus, the finding suggests that the 5-HTT gene variation doesn't cause anxiety by itself, but sets the stage for anxiety to develop in response to a sufficiently stressful situation.

More genes suspected

Researchers are currently investigating several other genes that may contribute to anxiety. A duplication on a region of chromosome 15 is especially common in families with high rates of panic disorder and phobia, according to a 2001 study in Cell. Potential genetic markers for panic disorder have also been found on chromosomes 1 and 11, and a possible marker for agoraphobia was found on chromosome 3.

Taken together, these findings amount to early evidence of a genetic basis for anxiety disorders. But because the study of genes related to anxiety is in its infancy, the particular genes involved and the ways in which their variations induce anxiety have yet to be uncovered. Thus far, no genetic tests are available to determine whether an individual is at higher risk for anxiety.

Last updated:	September 05, 2008