GRM5 and Alzheimer disease: Aβ oligomer interactions with mGluR5-PrPC may function to accelerate Aβ production through the FMRP dependent signaling pathway, suggesting that a positive feedback loop may exist in AD, whereby translation of APP results in increased substrate for amyloidogenic processing and generation of Aβ which then stimulates mGluR5 signaling to induce further synaptic synthesis of APP (Westmark and Malter, 2007; Westmark, 2013) (Figure 1B).