APP and Alzheimer disease: mGluR5 have been implicated in the toxic effects of amyloid Aβ pathology in AD, where mGluR5 stimulation can increase the expression of the amyloid precursor protein APP (Westmark and Malter 2007), and Aβ oligomers engage the mGluR5-PrP complex to initiate toxic signaling events (Hamilton et al. 2015; Renner et al. 2010; Um et al. 2013).