GRIA4 and major depressive disorder: GRIA4 encodes a subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors that underlie excitatory synaptic transmission and activity-dependent synaptic plasticity (Bettler and Fakler, 2017) and has been implicated in a range of human phenotypes, including schizophrenia (Marshall et al., 2017), substance use, and major depression.