In FXS, FMRP is progressively developmentally regulated with epigenetic silencing of the FMR1 gene that begins around 10 to 13 weeks of gestation (Willemsen et al., 2002; Li et al., 2020), and cognitive and behavioral FXS characteristics emerging during early childhood (2- to 3-year-old). The gene discussed is FMR1; the disease is fragile X syndrome.