We first performed peripheral blood bulk RNA sequencing (RNA-seq) to explore baseline gene regulation in children with chromatin-related NDDs (Kabuki syndrome (KMT2D, n ​= ​4), CHARGE syndrome (CHD7, n ​= ​2), and Rett syndrome (MECP2, n ​= ​5), and children with NDDs but without a monogenic diagnosis (non-monogenic, n ​= ​8), compared with sex-matched healthy controls (total n ​= ​21). The gene discussed is MECP2; the disease is atypical Rett syndrome.