Using the pons as the reference region in ROI analysis, we found significantly reduced mGluR5 availability in the hippocampus (SUVr: 1.18 ± 0.11 vs. 1.01 ± 0.13, p < 0.001) and parahippocampal gyrus (SUVr: 1.13 ± 0.11 vs. 1.01 ± 0.08, p < 0.001) in AD patients (Fig. 1A). This evidence concerns the gene GRM5 and Alzheimer disease.