In the present study, we have investigated gene–gene interactions of the three dopaminergic genes, DRD2/ANNK1, COMT and DBH. We genotyped seven SNPs of the three loci in a Chinese predominantly adult cohort that had been exposed to the 2008 Whenchuan earthquake and identified DRD2/ANNK1–COMT interaction that was associated with PTSD. The gene discussed is DBH; the disease is post-traumatic stress disorder.