Pharmaco-epidemiological evidence also points to potential mechanistic links: longitudinal analysis indicates that use of dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists is associated with reduced PD incidence (incidence rate ratios [IRRs] of 0.64 and 0.38, respectively) [5]. This evidence concerns the gene DPP4 and Parkinson disease.