GRM5 and fragile X syndrome: However, overexpression of mGluR5 secondary to absence of FMRP may lead to reduced 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl)propanoic acid/N-methyl-D-aspartate receptors as well as alterations in several other signaling molecules; thus, FXS is currently considered a disease of dysregulated neuronal signaling [5].