MECP2 and Rett syndrome: O-GlcNAcylation defects at the threonine 203 site in the mutations of the X-linked methyl-CpG-binding protein 2 (MECP2) gene, known as the main cause of RTT, have been reported to be associated with several dysfunctions in neurodevelopment and synaptic transmission in both cultured cells and the developing mouse cortex [123].