ID4 and atypical Rett syndrome: Despite ID subfamily genes (ID1, ID2, ID3, and ID4) have been identified as epigenetic targets in the regulation of neuronal maturation and the molecular pathogenesis of Rett syndrome (RTT), the role of ID3 in neurodegenerative conditions and in the pathogenesis of AD is not known yet (Peddada, Yasui, & LaSalle, 2006).