MECP2 and Rett syndrome: Classic Rett syndrome (RTT) is a childhood neurologic disorder affecting ∼1 in 10,000 live female births that results from loss-of-function mutations in the X-linked gene MECP2 (methyl-CpG-binding protein 2), encoding a multifunctional protein that regulates gene expression and chromatin architecture by interacting with methylated nucleotides (Amir et al., 1999; Lyst and Bird, 2015).