FMR1 and fragile X syndrome: The main genetic mutation that causes FXS is a trinucleotide repeat expansion of the sequence cytosine, guanine, guanine (CGG), with 200 or more repeats in the 5’ untranslated promoter region of the fragile X messenger ribonucleoprotein 1 (FMR1) gene (>200 repeats represents full mutation [FM]), which encodes the FMRP protein and is located on the X chromosome [2, 3].