ADCYAP1R1 and post-traumatic stress disorder: In humans, the PTSD-related PAC1R risk allele is associated with enhanced startle to threat-related cues, impaired fear and safety discrimination, and altered hippocampal and amygdala reactivity in fear conditioning (Ressler et al., 2011; Jovanovic et al., 2013; Stevens et al., 2014).