MECP2 and atypical Rett syndrome: An abnormal upregulation in the spontaneous turnover of pyramidal neuron dendritic spines has been observed across several mouse models of autism including the MECP2-duplication mouse (Chow et al., 2009; Cruz-Martín et al., 2010; Jiang et al., 2013; Isshiki et al., 2014; Gdalyahu et al., 2015; Ash et al., 2018), while mouse models of Rett syndrome exhibited decreased dendritic spine motility (Landi et al., 2011), suggestive of an abnormal balance between synaptic stability and plasticity.