FMR1 and fragile X syndrome: Extensive studies with two FXS animal models, the fmr1 knockout mouse and dfmr Drosophila (fruit fly) mutant, have demonstrated abnormalities in metabotropic glutamate (mGluR) [3] and γ-aminobutyric acid (GABA) [17] receptor signaling due to loss of normal inhibitory control of dendritic translation in the absence of FMRP.