Angelman syndrome is caused by:

Two microdeletion syndromes, Prader-Willi syndrome (PWS) and Angelman syndrome (AS), exhibit parent-of-origin, or "imprinting," effects. For many years, it has been known that cytogenetically detectable deletions of chromosome 15 occur in a propoion of patients with PWS, as well as in those with AS. New insight into the pathogenesis of these disorders has been provided by the recognition that parental origin of the deletion determines which phenotype ensues: if the deletion is paternal, the result is PWS, whereas if the deletion is maternal, the result is AS Ref: Harrison's principle of internal medicine 17th edition, chapter 64.