Acquisition of TET2 mutations is an early clonal event in MPN with mutations in Janus kinase 2 (JAK2) and myeloproliferative leukemia oncogene (MPL), implying that loss of 5-hmC levels may have a functional role in the onset and/or progression of hematological malignancies [96,112]. The gene discussed is JAK2; the disease is myeloproliferative disorder.