GIP and Parkinson disease: There is interest in the potential neuroprotective role of the incretin hormone glucagon-like peptide 1 (GLP-1) in PD based on compelling evidence in vitro, in rodent models, and in humans (Athauda and Foltynie, 2016; Kim et al., 2017; Bayram and Litvan, 2020; Glotfelty et al., 2020; Li et al., 2020; Salles et al., 2020; Zhang et al., 2020; Wang et al., 2021).