Athauda et al. conducted a randomized controlled trial (RCT) testing exenatide, a GLP-1 agonist, on moderate PD patients by subcutaneous injection once weekly for 48 weeks, its findings showed improvement in the exenatide group over the placebo group in the motor function assessed by MDS-UPDRS III at OFF-medication state with adjusted mean difference of − 3.5 points (Athauda et al. 2017). This evidence concerns the gene GCG and Parkinson disease.