Genetic and hormonal sensitivity to threat: testing a serotonin transporter genotype × testosterone interaction.

BACKGROUND Striking parallels are observed when comparing the literature on the 5-HTTLPR of the serotonin transporter gene (SLC6A4) to the testosterone (T) literature on measures of stress reactivity and neural activity. Short (S) allele carriers and individuals higher in testosterone levels show exaggerated stress responses, amygdala hyperactivity, and reduction of amygdala-prefrontal cortex coupling when exposed to threat. METHODS Three studies tested the hypothesis that higher T, S carriers would show increased cortisol responses to threat. RESULTS Supporting the hypothesis, a T × 5-HTTLPR interaction was obtained across all studies. Threats to status via social exclusion (Study 1), cognitive/perceptual failure (Study 2), and physical competence (Study 3) all produced elevated cortisol levels in S carriers with higher T levels. An unexpected result was that 5-HTTLPR long (L) allele homozygotes with higher T showed lower cortisol levels in response to threat-a pattern of response that closely parallels that reported for psychopathic individuals. Finally, combining effect sizes across studies showed that the likelihood that these effects were due to Type 1 errors was quite low. CONCLUSIONS What emerges from these studies is a novel yet reliable, and synergistic relationship between 5-HTTLPR genotype and testosterone on stress reactivity, possibly conferring vulnerability for multiple neuropsychiatric disorders.