Since our prior finding of reduced cerebral mGluR5 expression in cortical and subcortical regions of men with FXS has been confirmed [41,63], we sought expand the previous protocol of cerebral mGluR5 expression alone with a more refined measure tool to include simultaneous FRMP levels and cerebral mGluR5 expression for clinical trials of FXS. This evidence concerns the gene GRM5 and fragile X syndrome.