A 55–200 expanded CGG nucleotide repeats in the 5′-UTR of the fragile X mental retardation one gene (FMR1) constitutes the genetic hallmark of premutation carriers (OMIM#300623), whereas >200 repeats give rise to Fragile X syndrome (FXS; OMIM#300624), the leading inherited form of cognitive impairment (Kogan et al., 2008; Tassone et al., 2012; Battistella et al., 2013). Here, FMR1 is linked to fragile X syndrome.