FMR1 and fragile X syndrome: Methylation and transcriptional silencing of the Fragile X Messenger Ribonucleoprotein 1 (Fmr1) gene, due to the abnormal expansion of the trinucleotide CGG repeats in the promoter to over 200, leads to loss of encoded protein (FMRP), resulting in Fragile X syndrome (FXS) [19].