Therefore, due to the absence of FMRP in FXS, the translation of many of these mRNAs is upregulated including STEP mRNA (Huber et al., 2002; Hou et al., 2006; Gross et al., 2010; Darnell et al., 2011; Chatterjee et al., 2018). Here, FMR1 is linked to fragile X syndrome.