Several mGluR5 NAMs have been investigated for the treatment of drug addiction (Gass et al., 2009), FXS (Bear et al., 2004), Parkinson’s disease L-dopa-induced dyskinesia (Dekundy et al., 2006; Johnston et al., 2010; Grégoire et al., 2011), and depression (Palucha and Pilc, 2007), showing promising results in animal models. Here, GRM5 is linked to fragile X syndrome.