POU5F1 and Angelman syndrome: Moreover, on a more general genomic scale it has been shown that maintenance of imprinting marks in early zygotic development requires not only protection against postfertilisation demethylation, but also protection against somatic remethylation.14 A similar requirement for OCT4/SOX2-binding elements to maintain the maternal demethylated state has been found in the Prader-Willi/Angelman syndrome imprinting centre.15