Post-traumatic stress disorder is associated with PACAP and the PAC1 receptor. (2011).  The ‘CC’ allele was most robustly associated with total PTSD symptoms and among subscales, hyperarousal symptoms were the most strongly associated with rs2267735. Notably, even after controlling for childhood trauma history and adult trauma, age and race, the rs2267735 ‘CC’ allele was associated with higher levels of PTSD hyperarousal symptoms compared to ‘G’ carriers in women (p = 0.0008), but not men (p=0.51). ... Hyperarousal is the most robustly associated symptom with rs2267735 genotype (p = 0.0009). Fear discrimination (CS+ Startle minus CS− Startle) is impaired in females with rs2267735 ‘CC’ genotype. Dark enhanced startle (StartleDark – StartleLight) is significantly increased in females with rs2267735 ‘CC’ genotype.