GRIN2B and Alzheimer disease: A few studies have reported that levels of both GluN2A and GluN2B NMDA receptor subunit mRNA and protein were decreased in AD brain (Bi and Sze, 2002; Hynd et al., 2004), while levels of GluN2C and GluN2D mRNA did not differ from that of controls (Hynd et al., 2004).