Interestingly, Kcc2 overexpression or downregulation leads to changes in synaptogenesis, including dendritic spines that resemble those in patients with FXS and Fmr1 KO mice (Irwin et al., 2001; Li et al., 2007; Fiumelli et al., 2013; Awad et al., 2018). Here, SLC12A5 is linked to fragile X syndrome.