UBE3A and Kleefstra syndrome: Using NGS, in only five years more than eighty genes were related to the RTT-like phenotype and some of these genes were identified as causative for aRTT or RTT-like phenotype in these patients, although some of them were associated with well-known syndromes such as Pitt–Hopkins syndrome (TCF4, CNTNAP2 and NRXN1 genes), Phelan–McDermid syndrome (SHANK3 gene), Angelman syndrome (UBE3A gene), Kleefstra syndrome (EHMT1) and Cornelia de Lange syndrome (SMC1A).