FMR1 and fragile X syndrome: Thus, because of the technical advantages, we tried to test the ‘mGluR theory of FXS' by investigating the impact of a specific mGluR negative modulator, Fenobam, on the behavior of mice lacking FMRP (‘fragile X mental retardation 1 knockouts' or ‘Fmr1 KO mice’) using the multifunctional, motor-cognitive assay on the Erasmus Ladder.