GRM1 and atypical Rett syndrome: Collectively, these data demonstrate that non-ionotropic mNMDAR signaling strongly modulates the intracellular consequences of activating mGluR1/5, which have been linked to pathophysiology in several NDDs that, in addition to fragile X, include TSC,42,69SYNGAP1 haploinsufficiency,46 Rett syndrome,70 chromosome 16p11.2 microdeletion syndrome,71 and autism.72