August 13, 2008

Gene Linked To Anxiety Issues

A gene may be to blame in explaining why some people are more apt for anxiousness, according to a new study.

Known as COMT, this gene regulates the brain chemical dopamine. It also controls an enzyme that helps break down that chemical.

German researchers found that people with a particular, common variant of the gene tend to have an exaggerated "startle" response, which is a trait that could make them more vulnerable to anxiety disorders.

The findings came from the journal Behavioral Neuroscience. The study supports past studies that have found a link between the gene variant and a higher risk of anxiety disorders.

"This single gene variation is potentially only one of many factors influencing such a complex trait as anxiety," lead researcher Dr. Christian Montag, of the University of Bonn.

"Still," he added, "to identify the first candidates for genes associated with an anxiety-prone personality is a step in the right direction."

The researchers hope they can improve treatments by understanding the genetic underpinnings of anxiety and other psychiatric disorders.

Montag's team recruited 96 young German women who were an average of 22 years old to examine the relationship between COMT gene variants and the startle reflex.

There are two major variations of the COMT gene, one known as Val158 and the other Met158.

About half of the population carries one copy of each variant; the other half carries two Val copies (about 25 percent) or two Met copies (about 25 percent).

Those who carry two Met variants have the lowest activity in the COMT gene. That means they break down dopamine more slowly and therefore have higher levels of the chemical in emotion-regulating centers of the brain.

Based on the new findings, these individuals also have a stronger startle response.

To measure the startle reflex, Montag and his colleagues outfitted the women with electrodes that measured activity in their eye muscles as they viewed different computer images; some images were pleasant -- babies and animals, for instance -- some were emotionally neutral, and some were unpleasant -- such as pictures of weapons or injury victims.

During the experiment, a loud white noise would randomly sound as the women viewed the images. It elicited a startle reflex -- here measured as activity in the eye muscles.

Montag's team found that when women viewed an unpleasant image, those with two Met gene variants had a stronger startle response than those who carried at least one Val variant.

The researchers hypothesized that higher dopamine levels in the brain may make Met carriers feel more vulnerable to environmental threats or may make them less able to divert their attention from perceived threats.

According to Montag, the Met variant is seen only in humans, and not in other primates.

He speculates that the gene variant gives humans a level of "wariness" to protect them in a threatening world.

"It was an advantage to be more anxious in a dangerous environment," he noted.


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