MECP2 and Rett syndrome: In fact, Mecp2 null cortical astrocytes cause abnormal dendritic arborization in wild-type (WT) neurons and, similarly, mutant astrocytes differentiated from isogenic induced Pluripotent Stem Cells (iPSCs) from RTT patients adversely affect neuronal morphology (Ballas et al., 2009; Williams et al., 2014).