GLP-1 and GIP receptors are expressed on neurons in the CNS in the cortex and other key brain areas relevant to AD and PD (Usdin et al., 1993; Merchenthaler et al., 1999; Nyberg et al., 2005; Hamilton and Hölscher, 2009; Cork et al., 2015; Graham et al., 2020). Here, GCG is linked to Parkinson disease.