Thus, it is possible that mGlu5 NAMs may exert antiparkinsonian effects as a monotherapy especially in early PD prior to extensive nigrostriatal degeneration, or they may prove useful as an adjunct to dopamine replacement therapies, allowing for lower doses of dopaminergic drugs, which may delay or prevent the development of dyskinesias known to be related to dose and duration of treatment [49]. This evidence concerns the gene GRM5 and Parkinson disease.