MECP2 and Rett syndrome: Loss of MeCP2 in RTT patients and mouse models is not associated with neuronal cell death or axonal degeneration, although neurons are smaller and more densely packed than normal, and exhibit reduced dendritic arborizations (Bauman et al., 1995), spine density and synapse number (Belichenko et al., 2009, 2008, 1997; Armstrong et al., 1995; Armstrong, 1992; Kishi and Macklis, 2010).