For instance, identified mutations in methyl CpG binding protein 2 (MECP2) are known to cause Rett syndrome (Rett, 1966; Amir et al., 1999; Trappe et al., 2001; Guy et al., 2007; McGraw et al., 2011; Chao and Zoghbi, 2012; Katz et al., 2012; Heckman et al., 2014), whereas mutations in CREB binding protein (CBP) cause Rubinstein-Taybi syndrome. Here, CREBBP is linked to atypical Rett syndrome.