DPP4 and Parkinson disease: In comparison with DPP4 inhibitor nonusers, both the patients with DDD greater than 0.32 and DDD less than 0.32 showed a significant decrease in PD incidence (aHR, 0.50; 95% CI 0.35–0.71 and aHR, 0.53; 95% CI 0.36–0.77, respectively).