Since the discovery that mutations in the transcriptional regulator Methyl-CpG-binding protein 2 (Mecp2) underlie the vast majority of RTT cases, studies in mouse models of RTT have implicated virtually every resident brain cell type (neurons and glia) in the disorder (Amir et al., 1999; Guy et al., 2011; McGann et al., 2012; Lyst and Bird, 2015; Li, 2012). Here, MECP2 is linked to Rett syndrome.