GRM5 and Alzheimer disease: Recent evidences have suggested that amyloid beta oligomers (Aβo) in AD mediate synaptotoxic signaling through PrPC and mGluR5, while α-synuclein-PrPC interaction induces cognitive impairment through mGluR5 and NMDAR2B (Um et al., 2013; Hamilton et al., 2015; Beraldo et al., 2016; Ferreira et al., 2017).