Specific glutamatergic effects probed in humans with FXS have included antagonism of group I metabotropic glutamate receptors (mGluRs), particularly mGluR5 (ClinicalTrials.gov Identifiers: NCT01253629, NCT01357239, NCT01517698, NCT01015430, NCT01750957), the N-methyl-D-aspartate (NMDA) receptor, stimulation of GABA(B) receptors (NCT01325220, NCT00788073, NCT01282268), and modulation of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptor (AMPAR; NCT00054730). This evidence concerns the gene GRM5 and fragile X syndrome.