FMR1 and fragile X syndrome: Consistent with this underlying mechanism of mGluR overactivity in FXS, MPEP (2-methyl-6-(phenylethynyl)-pyridine) and other mGluR negative modulators have been shown to reverse multiple phenotypes in the fmr1 knockout mouse, including audiogenic seizures, epileptiform discharges and open field hyperactivity,13, 14 as well as impairments in courtship memory in dfxr mutant Drosophila15 models.