Through a normal biological process called genomic imprinting, the chromosome 15 that is inherited from the father has a set of genes that are switched on while the same set of genes on the chromosome 15 inherited from the mother are switched off. In Prader-Willi syndrome (PWS), there is no normal copy of the paternal chromosome 15 so patients only have the switched off copies that came from the mother’s chromosome 15. My laboratory has identified an important component of the switch off mechanism, a protein called ZNF274. In this proposal, we have destroyed ZNF274 in stem cell lines created from PWS skin cells. We have succeeded in switching on the set of genes in the maternal chromosome 15 in brain cells produced from ZNF274-less PWS stem cells. Our goal is to confirm that targeting ZNF274 for destruction provides an approach to improving the symptoms of PWS. We are using new approaches to engineer ZNF274-less PWS stem cells with the goal of better understanding the PWS disease mechanism and discovering new PWS drug targets. We are also producing so-called “mini-brains” from ZNF274-less PWS stem cells to ask if the maternal genes, which have been rescued from the off state, stay active. The stem cell “mini-brains” could offer a more realistic model of the PWS brain gene abnormalities. We hope are also testing a new approach to interfering with ZNF274 binding that will turn on the genes that are switched off PWS without affecting the activity of other important genes.