Overall, TET2 mutations have been described in about 14% of MPN, 23% of MDS (in which they usually occur together with mutations in SF3B1, U2AF1, ASXL1, SRSF2 and/or DNMT3A and also a normal karyotype [124]) and 30% of CMML patients (often associated with mutations in the SRSF2 and U2AF1 genes) [10,91,124,134,146]. The gene discussed is ASXL1; the disease is myelodysplastic syndrome.