SUZ12 is one of the core components of the polycomb repressive complex 2 (PRC2), which is a highly conserved histone H3 lysine 27 methyltransferase that regulates the expression of developmental genes. SUZ12 mutations are present infrequently (<2%) in myeloproliferative neoplasms (MPN) and myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN). The mutations are missense and tend to be located at the highly conserved VEFS domain, is required for the interaction between SUZ12 and EZH2. These mutations reduced PRC2 histone methyltransferase activity in vitro. Inactivating mutations of the catalytic component of PRC2, EZH2, can also be seen in myeloid neoplasms. Mice with loss of function mutations in PRC2 components display enhanced activity of their hematopoietic stem cell/progenitor population and loss of SUZ12 function in particular enhances hematopoietic stem cell activity.