Based on previous research that metabotropic glutamate receptor 5 (mGluR5) signaling is altered in FXS [95,96], the authors investigated the effects of a selective mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) on neuronal differentiation in FXS hiPSC-derived NPCs and Fmr1-KO mouse NPCs [62]. This evidence concerns the gene GRM5 and fragile X syndrome.