FMR1 and fragile X syndrome: The majority of males with FXS express some FMR1 mRNA and this incomplete silencing of the promoter is associated with increased autistic features [46,47,48,49], In males, full mutation FXS with complete or incomplete methylation silencing of the FMR1 gene is associated with increased inappropriate speech on the ABC-C sub-scale compared to the FXS group mosaic for pre- and full mutation alleles, and mosaicism in either sex is associated with less maladaptive behaviors [50,51].