Model mice with Silver-Russell syndrome has been successfully generated by TET1-dCas9 based system.332 TET1-based DNA methylation editing could restore the expression of FMR1 by demethylating its promoter, supporting the potential application of epigenome editing in fragile X syndrome treatment.333 Similarly, TET1-dCas9 mediated demethylation of the MECP2 promoter, rescued Rett syndrome neurons.334 Thus, precise and efficient epigenetic editing tools would provide new insights into the functions of the specific DNA modification locus temporal-spatially. The gene discussed is TET1; the disease is atypical Rett syndrome.