CTCF and Rett syndrome: More recently, Liu and colleagues combined dCas9-Tet1-based demethylation with locus-specific recruitment of CTCF using dCpf1-CTCF fusion proteins to reactivate Mecp2 expression from the inactivated X chromosome in neurons, which rescued the functional deficits of Rett syndrome in vitro (Qian et al, 2023).