FMR1 and fragile X syndrome: Most FXS disease cases result from the expansion of CGG repeats (>200) in the 5’ untranslated region of the Fragile X Mental Retardation 1 (FMR1) gene (Hagerman et al., 2017), leading to epigenetic hypermethylation and loss of the gene product Fragile X Mental Retardation Protein (FMRP) (Bagni and Zukin, 2019).