GRIK1 and glioblastoma: An overall down-regulation of ionotropic receptor expression - NMDA (NR1, NR2A–C, NR3A), AMPA (GluR1–4) and kainate (GluR5,7; KA2) receptor - was observed between the controls and the GBM patients, which was statistically significant as calculated by Student's t-test (p<0.0001).