The genetics of fear: Study suggests specific genetic variations contribute to anxiety...( Polymorphisms are variations in gene...)

Polymorphisms are variations in genes which can result in changes in the way a particular gene functions and thus may be associated with susceptibility to common diseases. In a new study in Psychological Science, a journal of the Association for Psychological Science, psychologist Tina B. Lonsdorf and her colleagues from the Karolinska Institutet in Sweden and the University of Greifswald in Germany examined the effect of specific polymorphisms on how fear is learned and how that fear is subsequently overcome.

Many symptoms of anxiety disorders are thought to be learned and research on fear conditioning (a method of learning to fear a particular stimulus) shows that individuals diagnosed with anxiety disorders are quick to learn to fear a stimulus but have a difficult time getting rid of that fear. In this study, the researchers focused on polymorphisms in two genes thought to play a role in anxiety disorders: the serotonin transporter gene and the gene for the enzyme COMT.

Serotonin is a brain chemical involved in mood regulation. The serotonin transporter, which is the target of selective serotonin reuptake inhibitors (SSRI) used to treat anxiety and depression, harbors a common polymorphism in its gene. This polymorphism can come in two different versions that differ in their length. The shorter version of the gene leads to less serotonin being cleared away and is also associated with higher neuroticism scores and anxious behavior. The COMT enzyme is involved in breaking down dopamine, a brain chemical important for learning, motivation and seeking rewards. A specific polymorphism in this gene results in higher levels of extracellular dopamine in the prefrontal cortex, leading to enhanced working memory but also greater levels of anxiety.

In this experiment, volunteers were shown a picture (A) and then immediately received a mild electric shock. They were also shown another picture (B) that was never associated with a shock.
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