GRIK4 and glioma: In addition to AMPA receptor, other ionotropic glutamate receptor genes are also used in the 17-gene set, including N-Methyl-D-aspartate (NMDA) receptor [GRIN3A (Marco et al., 2013), GRIN2C (Collingridge et al., 2009)], kainate receptor [GRIK4 (Arora et al., 2018)], and non-classical glutamate receptor such as glutamate delta-1 receptor [GRID1 (Gupta et al., 2015)], suggesting that other ionotropic glutamate receptors also perform important functions in gliomas.