Pituitary adenylate cyclase-activating polypeptide (PACAP) in peripheral blood is associated with PTSD symptoms in females, while a single nucleotide polymorphism in the PAC1 receptor gene (ADCYAP1R1) is associated with PTSD symptoms in females, and shows fear- and estrogen-induced expression [6]. This evidence concerns the gene ADCYAP1 and post-traumatic stress disorder.