The genetics of fear

Monday August 11 2008

Scientists have identified a “Horror film gene that makes some scream while others laugh”, The Daily Telegraph reports. Results from a study of 96 women in Germany found that women who had two copies of one version of a gene called COMT “were significantly more startled by frightening images” than women who didn’t, the newspaper says.

This study used a test to measure how women responded to a startling burst of noise when shown pleasant, unpleasant or neutral images. Although this test is an accepted way of testing fear response, it is not clear how closely it resembles real-life fearful situations, or even watching horror movies. As the authors of the study point out in the news reports, anxiety and fear are complex emotions which will be affected by more than one genetic variation. Environmental factors will also play an important role.

Where did the story come from?

Drs Christian Montag, Martin Reuter and colleagues from the University of Bonn and other universities in Germany, Denmark and the US carried out this research. No sources of funding were reported for this study. It was published in the peer-reviewed scientific journal: Behavioural Neuroscience .

What kind of scientific study was this?

This was a cross-sectional study looking at the association between a genetic variation in the COMT gene and people’s brain activity when processing fear. The COMT gene encodes a protein that breaks down one of the chemicals used to communicate by nerve cells in the brain. The main genetic variation that the researches were interested in leads to a change in the 158th amino acid (building block) in the chain that makes up this protein, changing it from an amino acid called valine (Val158) to an amino acid called methionine instead (Met158). The Met158 variation means that the protein cannot breakdown the communication chemical as effectively, and this has been found to be associated with anxiety in some studies, although not others.

The researchers selected 101 white female participants of German origin (average age 22 years) from their database of healthy people who had volunteered to take part in behavioural research. In order to be included on the database, the volunteers had to report no symptoms of mental health disorders or neurological diseases. All database participants provided cheek swabs for extraction of DNA, and the DNA was tested for known genetic variations thought to be potentially related to behavioural traits, including the COMT variation.

The researchers selected people who had two, one or no copies of the COMT Met158 variation (each person has two copies of the COMT gene). The selected participants then took part in the “affective startle response modulation” test or ASRM. The ASRM was reported to be a standard test of fear processing, and other studies have shown that people with anxiety disorders and those with anxious temperament have enhanced responses on the ASRM. The test investigates the participants’ response to a stimulus designed to startle them (a loud burst of noise) while they look at pictures which should evoke different emotional responses. For the ASRM test, the participants sat in front of a computer screen wearing headphones and had sensors attached under their left eye that measured the electrical changes associated with eye blinking.

The researchers first tested the women’s response to loud bursts of noise through the headphones, with no pictures on the computer screen. The five women who did not show any eye blink response to this test were excluded from the study, leaving 96 participants. The researchers then tested the remaining women’s responses to the noise while they looked at 12 pleasant, 12 unpleasant and 12 neutral (neither pleasant or unpleasant) pictures on the screen. The pictures were shown in a random order. Pleasant pictures showed babies, animals or families; neutral pictures showed things such as power outlets or hair dryers; unpleasant pictures were threatening or fear-inducing, for example, injured victims at crime scenes or weapons. The researchers then compared the strength of the eyeblink response when looking at the different pictures in the women with two, one or no COMT Met158 variations.

What were the results of the study?

The researchers found that exposing the women to pictures increased their startle response to the loud noise, with no difference between the different types of pictures shown. When shown unpleasant pictures, women who carried two COMT Met158 variants showed a greater startle response than women who did not. There was also a trend for these women to show greater startle response when looking at neutral pictures, although this difference did not reach statistical significance. There was no difference in startle response in women who carried two COMT Met158 variants and those who didn’t when shown pleasant pictures.

What interpretations did the researchers draw from these results?

The researchers concluded that the COMT Met158 variation regulated fear processing, and this supports findings from previous studies that have found this variation to be associated with anxiety disorders.

What does the NHS Knowledge Service make of this study?

This study has a number of limitations that must be borne in mind:

  • Although the test used may be a standard way of measuring fear response, it is not clear how well this replicates what would happen in response to real-life situations that might induce fear.
  • The study uses a standard set of images to induce particular emotions; however, images that may be pleasant or unpleasant for one person may not be perceived in this way by others.
  • It included only relatively young women with no reported symptoms of mental health disorders, and therefore cannot be extrapolated to people with anxiety disorders, to men or to older populations.
  • The study was relatively small, and therefore its findings are more susceptible to occurring by chance than the findings of a larger study would be.

Analysis by Bazian
Edited by NHS Choices