Abstract

Studies of the association between polymorphisms of the serotonin transporter gene and fear learning have produced inconsistent results, raising questions about the strength of the rela-tionship and the methodological conditions under which the relationship occurs. We conducted a meta-analysis of existing studies to provide an integrated statistical measure of the effect of the polymorphic region of the serotonin transporter gene (5-HTTLPR) in aversive associative learning (acquisition and extinction) in humans and rodents. The included studies were gathered through scientific database search engines. Selection criteria included experimental studies in which 5-HTTLPR and any measure of fear were considered as main variables. An effect size was calcu-lated for each relevant experiment. 30 articles, with 33 experiments were included, 28 for acquisition, 13 for extinction. The integrated effect size (random effects model) for acquisition of fear was d = 0.33, 95 % CI [0.20, 0.50]. For extinction, the integrated effect size was d = 0.63, 95 % [CI 0.26, 1.00]. Test for publication bias was not significant neither for acquisition nor extinction. Thus, a medium but consistent effect was found between having the S allele of 5-HTTLPR and fear. The finding suggests a genetic vulnerability to anxiety in carriers of the polymorphism of the serotonin transporter that should be considered in future research.