MECP2 and Rett syndrome: Several in vivo and in vitro models exist for the study of RTT and MECP2 function, including Mecp2-null mutant mice (Chen et al., 2001; Guy et al., 2001); Xenopus laevis with truncated Mecp2 (Stancheva et al., 2003); induced pluripotent stem cells (iPSCs) from RTT patients' fibroblasts (Marchetto et al., 2010); mecp2-null mutant zebrafish (Pietri et al., 2013); and most recently transgenic monkeys overexpressing MECP2 (Liu et al., 2016).