In FXS, reduced GLT-1 and GLAST-1 increase glutamate levels [91,103] lead possibly to a depression of the synaptic transmission by mGluR5-mediated LTD, or are causative, at least to some extent, for the hyperexcitability that has been widely described in FXS [138,139,140]. The gene discussed is SLC1A2; the disease is fragile X syndrome.