UBE3A and Prader-Willi syndrome: The PWS-cr mice have loss of paternally expressed genes critical to the core phenotype of PWS, and the PWS-IC lose all paternal gene expression and also have 2-fold overdosage of maternal Ube3a. These two models both display the core phenotypes associated with PWS, including growth retardation [32, 33, 67], endocrine changes [32, 68], and hyperphagia [31, 69, 70].