Genetics of fear? 19/7/02. By the Public Health Genetics Unit A paper published in Science magazine reports the results of a study on the relationship between a genetic polymorphism in the gene encoding a protein that functions as a transporter of the neurotransmitter serotonin, and the response of a part of the brain called the amygdala to 'fearful stimuli'.

Two groups of 14 subjects each were matched for factors such as age, racial group, sex and handedness. Subjects in one group (s) had either one or two copies of the s (short) promoter allele of the serotonin transporter gene, while subjects in the second group (l) had two copies of the l (long) promoter allele.

These different forms of the serotonin transporter gene have been shown to be associated with different activity levels of the serotonin neurotransmitter, which plays a part in the physiological processes involved in fear and anxiety.

A magnetic resonance imaging technique was used to record the activity of the amygdala when the subjects were given a task in which they were asked to say which of two faces matched the emotion (anger or fear) on a simultaneously-shown target face. As a control, the subjects also completed a working memory task.

When carrying out the face-matching task, subjects with the s allele showed a greater response of the right amygdala than those homozygous for the l allele, but brain activity was the same for both groups during performance of the working memory task. The right amygdala is thought to be involved in the processing, by the brain, of angry or fearful facial expressions.

The authors conclude that the s/l serotonin transporter polymorphism plays a role in determining the brain response to fearful stimuli: those with the s allele have stronger reactions of fear and anxiety.

Public Health Genetics Unit comment: The polymorphism studied fulfils the criterion that there is a biologically plausible mechanism for its proposed effect: a considerable body of work supports a role for serotonin activity in emotional responses. However, with only 14 subjects in each group, the study was very small, and P values for measured differences between the groups were modest (0.02-0.05). At this stage, it seems premature for Science to bill this paper with the headline "Genetics of fear".

Article courtesy of the Public Health Genetics Unit .

Image credit: Matthew Herring

Further reading

Hariri AR, et al. Serotonin transporter genetic variation and the response of the human amygdala. Science 2002 297(5580):400-3. Abstract