High expression of LINE-1 was found in Rett syndrome caused by mutation of methyl CpG binding protein 2 (MeCP2) in the X-linked gene, which was caused by the inclusion of LINE-1 5′-UTR sequence in the MeCP2 target, leading to methylation-dependent repression (Muotri et al., 2010). This evidence concerns the gene MECP2 and Rett syndrome.