Additional studies have reported linkages between genes regulating glutamate transmission (GRIN1, GRIN2A, GRIN2B, GRM3, and GRM4), the stress response (ND4, NDUFV2, XBP1, and MTHFR), inflammation (PDE4B, IL1B, IL6, and TNF), apoptosis (BCL2A1 and EMP1), and oligodendrocyte-mediated myelination of white-matter tracts (eIF2B) in bipolar disorder (42, 59–62). Here, GRM4 is linked to bipolar disorder.