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In page Prader–Willi syndrome:

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Region 15q11-13 is implicated in both PWS and Angelman syndrome (AS). While PWS results from the loss of PW genes within this region on the paternal chromosome, loss of a different gene (UBE3A) within the same region on the maternal chromosome causes AS.[7] PWS and AS represent the first reported instances of disorders related to imprinting in humans.[citation needed]