GRM5 and fragile X syndrome: As expected from FXS’s neurobiology, the vast majority of the studies have targeted a core excitatory/inhibitory imbalance in the disorder (italized under M﻿echanism, Table 1) primarily through either mGluR5 antagonists (mavoglurant-AFQ056, basimglurant-RO4917523) or GABA agonists (arbaclofen-GABA-B agonist, ganaxolone-GABA-A agonist, acamprosate-GABA-A/GABA-B agonist).