FMR1 and fragile X syndrome: In summary, increased mGluRI signaling in Fmr1 KO mice: (1) is caused by a molecular mechanism that has not been yet fully elucidated; (2) it has never been shown to be true in human neuronal tissue; in vivo or in vitro; (3) it has failed to provide an effective drug target to ameliorate FXS; and (4) it has been shown to exist in many other mouse models of intellectual disability and ASDs, regardless of the Fmr1 KO mutation.