According to the denominated “metabotropic glutamate receptors (mGluR) theory of fragile X syndrome” proposed by Bear et al. in 2004 [78]: as a consequence of the synthesis of FMRP, this protein acts as an inhibitor of the translation of certain proteins that reduce the internalization of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Here, FMR1 is linked to fragile X syndrome.