Required to maintain a pool of extrasynaptic AMPA-regulated glutamate receptors (AMPAR) which is necessary for synapse development and function. Regulates basal AMPAR function and synaptic transmission during development but is dispensable at mature hippocampal synapses. Plays a role in regulating basal phosphorylation levels of glutamate receptor GRIA1 and promotes GRIA1 and GRIA2 cell surface expression. . This is the function of PRRT1 (proline rich transmembrane protein 1, ENSG00000204314).