Genetic variation of the serotonin transporter (SCL6A4, 5-HTT) has been associated with fear- and anxiety-related behaviors, while a polymorphism in exon III of the D4 dopamine receptor gene (DRD4) has been linked to novelty seeking.
These results demonstrate genetically driven variation in the response of brain regions underlying human emotional behavior and suggest that differential excitability of the amygdala to emotional stimuli may contribute to the increased fear and anxiety typically associated with the short SLC6A4 allele.