Scientists from Columbia University have used a new epigenetic editing technology to correct mutations in neurons that cause Rett syndrome, a rare X-linked neurodevelopmental disorder that primarily affects young girls and causes severe mental disability. The proof-of-concept work, reported in this week's Science Translational Medicine, may not only point to a potential treatment for Rett syndrome but also other X-linked diseases. Rett syndrome is caused by loss-of-function mutations affecting the methyl CpG-binding protein 2 (MECP2) gene on the X chromosome. In the study, the investigators used a multiplex epigenome editing approach to reactivate MECP2 from the inactive X chromosome in Rett syndrome-like human embryonic stem cells and derived neurons. The reactivation, they write, improved neuron-like function in vitro with no detected off-target effects. While promising, the approach still needs to be tested in animal models of Rett syndrome to determine the treatment's effect at behavioral levels before advancing into the clinic, the researchers note.