Fragile X syndrome (FXS) is caused solely by loss of fragile X mental retardation protein (FMRP), which binds mRNAs to mediate transcript stability and trafficking, and acts as a negative regulator of translation (Laggerbauer et al., 2001; Li et al., 2001; Zhang et al., 2001; Lu et al., 2004; Muddashetty et al., 2007; Tessier and Broadie, 2008). Here, FMR1 is linked to fragile X syndrome.