FXS is due to loss of function of the RNA-binding protein FMRP (Bagni et al., 2012, Bassell and Warren, 2008), which regulates dendritic targeting of mRNAs (Dictenberg et al., 2008) and controls protein synthesis and mRNA decay in neuronal soma and at synapses (Bassell and Warren, 2008). This evidence concerns the gene FMR1 and fragile X syndrome.