We first examined the expression levels of the genes encoding the mGlu3 and mGlu5 receptors (GRM3 and GRM5, respectively) in GBM samples from 83 patients and in samples of lower-grade gliomas from 15 patients; the overall analysis showed a greater expression of both mGlu3 and mGlu5 receptors in GBM with respect to lower grade gliomas (p = 0.0018 and p = 0.0221 respectively). This evidence concerns the gene GRM5 and central nervous system cancer.