As expected from FXS neurobiology, the vast majority of the studies have targeted the core excitatory/inhibitory imbalance in the disorder primarily through either mGluR5 antagonists (mavoglurant-AFQ056, NCT01357239, NCT01253629; basimglurant-RO4917523, NCT01517698, NCT01750957) or GABA agonists (arbaclofen-GABA-B agonist, NCT01282268, NCT00788073, NCT01325220; ganaxolone-GABA-A agonist, NCT01725152). Here, GRM5 is linked to fragile X syndrome.