CDKN1C and Pelizeaus-Merzbacher spectrum disorder: This is supported by the following facts: the presence of BWS in approximately 20% of PMD cases mentioned above [4,5,6,20]; the mosaicism of the maternal deletion of 11p15.5 found in placentas with PMD [68]; the partial trisomy (two paternal copies and one maternal copy) of 11p15.5 found in an enlarged placenta with edematous villi [69]; the limitation of pUPD11 to 11p in a biparental-PMD case [32]; and the placentomegaly and dysplasia that are observed in mice with a null mutation of Cdkn1c and loss of Igf2 imprinting [70].