FMR1 and Neurodevelopmental delay: FXS is a genetic neurodevelopmental disorder (NDD) caused by a trinucleotide expansion (>200 CGG repeats), the hypermethylation of the 5′UTR end of the fragile X messenger ribonucleoprotein 1 (Fmr1) gene, and consequent absence of the encoded protein, FMRP [11,12,13,14,15].