The G × G ADCYAP1R1-FKBP5 interaction (rs2267735 × rs1360780) was associated with PTSD severity (beta = −1.31 and P = 0.049) based on all subjects, and the G × G ADCYAP1R1-CRHR1 interaction (rs2267735 × rs242924) was correlated with PTSD severity in men (beta = −4.72 and P = 0.023). The gene discussed is FKBP5; the disease is post-traumatic stress disorder.