The authors put the accent on the evidence that nigrostriatal denervation in PD leads to increased glutamatergic transmission in the basal ganglia and that glutamate receptor stimulation is involved in the pathogenesis of levodopa-induced motor complications in PD and glutamate receptor subtypes, such as mGlu5 and NMDA receptors, are potential selective targets for treatment of these adverse effects. The gene discussed is GRM5; the disease is Parkinson disease.