The majority of FXS cases result from the epigenetic transcriptional silencing of the Fragile X Mental Retardation 1 gene (FMR1), which subsequently prevents the expression of fragile X mental retardation protein (FMRP) (Pieretti et al., 1991; Verkerk et al., 1991; Coffee et al., 1999, 2002; Eiges et al., 2007). Here, FMR1 is linked to fragile X syndrome.