Further support for a role of group I mGluR receptors in the pathogenesis of PD and DLB steams from studies showing that mGluR5 antagonists ameliorate the behavioral alterations in animal model of parkinsonism [38], [39], [40], [41] and are neuroprotective against MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in animals [42], [43]. This evidence concerns the gene GRM5 and Parkinson disease.