The GLP-1 receptor agonist Exendin-4 prevents 6-hydroxydopamine (6-OHDA)-induced death of dopaminergic neurons in neuronal culture (Li et al., 2009; Athauda and Foltynie, 2016), and intraventricular administration protects mice from MPTP-induced dopaminergic cell loss and improves motor function in animal models of PD (Li et al., 2009). This evidence concerns the gene GLP1R and Parkinson disease.