A new epigenetic editing technique has restored the functionality of neurons in Rett syndrome (RTT), a rare neurodevelopmental disease associated with a mutation of the MECP2 gene on the X chromosome. The origin of this disorder is a heterozygous mutation of the MECP2 (methyl CpG-binding protein 2) gene. Homozygosity is lethal and as it is associated with the X chromosome; Rett mostly affects girls, inhibiting the development of their motor skills and communication.