It has been revealed that the expression of mGluR5 is increased in the dopaminergic brain region of PD, and this mGluR5 is also known to interact and boost the activity of ionotropic NR2B containing NMDAR by phosphorylating the NR2B subunit, leading to Ca2+ imbalance and neurotoxicity [117,139,140]. Here, GRM5 is linked to Parkinson disease.