Enhanced hippocampal group I mGluR-LTD is a well-described feature of Fmr1 KO mice [35], which eventually led to the hypothesis that such anomalous synaptic plasticity could be related to the intellectual disability in FXS [5], and that treatments targeting mGluR5 could improve the cognitive deficit in FXS [36]. Here, GRM5 is linked to fragile X syndrome.