GRM5 and Alzheimer disease: Hippocampal mGluR5 binding remained significantly lower in AD than in CN participants with GM masking (BPND = 1.30 ± 0.33 vs. 1.78 ± 0.61, p = 0.011) and PVC (BPND = 2.19 ± 0.45 vs. 2.69 ± 0.88, p = 0.0499).