FXS is caused by silencing of the Fmr1 gene coding for Fragile X Mental Retardation Protein (FMRP) (Pieretti et al., 1991), an mRNA binding protein that functions as a regulator of protein translation (Laggerbauer et al., 2001; Bechara et al., 2009). The gene discussed is FMR1; the disease is fragile X syndrome.