GRIA4 and glioblastoma: Follow-up studies proved the existence of ionotropic GluR1 and GluR4 (Korczak et al. 1995), GluR2/3/4/6/7, KA1 (Yoshioka et al. 1996)], NR1 and NR2C (Casado et al. 1996), or GluR1/2/3/4 in surgical samples of glioblastomas (Ishiuchi et al. 2002) along with various other combinations of subunits in cell lines and CNS tumor samples (Aronica et al. 2001; de Groot et al. 2008).