Several authors, to clarify the neurobiology of RTT and FXS, investigated the molecular targets of MeCP2 and of FMRP (Skene et al., 2010; Darnell et al., 2011; Baubec et al., 2013; Maxwell et al., 2013; Gabel et al., 2015; Rube et al., 2016; Maurin et al., 2018; Sawicka et al., 2019). Here, MECP2 is linked to fragile X syndrome.