Anxiety may be partly genetic
Variations in a gene may help explain why horror movies shock some people and entertain others, say German scientists.
People with one version of the COMT gene startled more dramatically to unpleasant images than others, the researchers found.
The work in Behavioural Neuroscience suggest inborn differences make some prone to extreme anxiety and stress.
Anxiety treatments could be tailored to fit these genes, the authors suggest.
The COMT gene weakens the effect of a signalling chemical (dopamine) in the brain linked to emotion.
Dr Martin Reuter and his colleagues at the University of Bonn measured the "startle response" of 96 women with different variations of the gene by attaching electrodes to their eye muscles.
When a person is startled upon emotional arousal the eyes automatically blink.
The women were shown sets of pictures that were emotionally pleasant (such as animals or babies), neutral (such as an electric plug or hair dryer) or aversive (such as weapons or injured victims at a crime scene).
A loud noise was made at random while they watched to startle the volunteers.
In the genes
The women who carried the two copies of the Met158 variation of the COMT gene startled more easily than those carrying two copies of the Val158 variation.
The Met158 carries also scored higher on anxiety on standard personality tests.
Met158 is found in about half the population but it exerts its effect on the one in four people who have inherited both copies of it from their parents, say the researchers.
Co-researcher Dr Christian Montag said: "This single gene variation is potentially only one of many factors influencing such a complex trait as anxiety.
"Still, to identify the first candidates for genes associated with an anxiety-prone personality is a step in the right direction."
He added: "It might be possible to prescribe the right dose of the right drug, relative to genetic makeup, to treat anxiety disorders."
Dr George Fieldman, Psychologist at Buckingham New University and member of the British Psychological Society, said possessing the Met158 variation could be beneficial from an evolutionary perspective.
"Natural selection codes for survival, not comfort. This gene, although uncomfortable, could be beneficial to survival."
It can be advantageous to be more anxious in a dangerous environment, he said.