FXS is caused by a Cytosine-Guanine-Guanine (CGG) repeat expansion of over 200 on the 5′ untranslated region of the Fragile X messenger ribonucleoprotein 1 gene (FMR1) on the X chromosome, inhibiting the production of Fragile X messenger ribonucleoprotein 1 (FMRP), an essential protein for several aspects of brain development (22, 23). Here, FMR1 is linked to fragile X syndrome.