mGluR5, which is ubiquitously expressed in the brain, is considered to be partially responsible for memory and learning and plays a key role in regulating neuronal transmission and synaptic strength, and it has been suggested that aberrant mGluR5 signaling is involved in mediating multiple aspects of cognitive deficits associated with AD.47, 54, 55. This evidence concerns the gene GRM5 and Cognitive impairment.