Over 200 CGG repeats in the 5′-UTR of FMR1 cause Fragile X syndrome (FXS) [16], the most common inherited form of intellectual disability, due to transcriptional silencing induced by DNA methylation of the CGG trinucleotides and loss of the FMRP protein which has roles in synaptic plasticity. The gene discussed is FMR1; the disease is Intellectual disability.