In addition, common anti-diabetic treatments such as dipeptidyl peptidase-4 (DPP4) inhibitors, glucagon-like peptide-1 (GLP-1) agonists and metformin have shown promise in the treatment of PD and cognitive impairment in human and animal models of PD (Ashraghi et al., 2016). This evidence concerns the gene DPP4 and Parkinson disease.