GRM2 and Down syndrome: The results of this study are consistent with previous studies that have shown increased expression or activation of glutamate receptors in the acute neurotoxicity rodent [43] and primate [64] models of PD and in other neurodegenerative disorders with protein accumulation such as Amyotrophic lateral sclerosis (mGluR5; [65]), Down's syndrome (mGluR5; [66]), and AD (mGluR2/3; [32], [67], [68], [69]).