MECP2 and Rett syndrome: Consistently, the evolutionary analysis revealed that non-CpG methylation is confined to vertebrates and enriched within a highly conserved set of developmental genes silenced in adult brains, and MeCP2 originated at the onset of vertebrates, suggesting the emergence of non-CpG methylation and its reader may facilitate the evolution of sophisticated cognitive abilities of vertebrate lineage.169 As a result, loss-of-function mutations in the MECP2 gene cause a severe neurological disorder known as RTT.