GRM2 and glioblastoma: It was observed that the majority of invasive gliomas either lack GluR2 expression (Lyons et al. 2007) or GluR2 is expressed at significantly lower levels, as demonstrated in highly malignant pediatric glioblastomas, ependymomas or medulloblastomas (all WHO III or IV) in contrast to low-grade astrocytomas (WHO I or II) (Brocke et al. 2010).