GCG and Parkinson disease: Various synthetic incretin analogs, such as exendin-4, liraglutide, lixisenatide, semaglutide, (Val8)GLP-1-Glu-PAL, NLY01, or GLP-1R/GIPR dual agonists, were shown to prevent the atrophy of dopaminergic neurons in the SN and striatum (Oh et al., 2006; Bertilsson et al., 2008; Harkavyi et al., 2008; Kim et al., 2009; Li et al., 2009; Liu et al., 2015a; Zhang et al., 2015, 2018, 2020; Cao et al., 2016; Ji et al., 2016; Jalewa et al., 2017; Yun et al., 2018; Lv et al., 2021; Zhang L.Y. et al., 2021) and preserve dopaminergic fibers in PD animal models (Bertilsson et al., 2008; Kim et al., 2009).