In FXS, CGG triplet expansion in the fragile X mental retardation gene (Fmr1) prevents the synthesis of the fragile X mental retardation protein (FMRP) (De Rubeis and Bagni, 2010), causing anatomical and functional alterations, such as abnormal dendrite spines morphology and dysfunctions in synaptic plasticity (Zalfa et al., 2006). Here, FMR1 is linked to fragile X syndrome.