SF3B1 (splicing factor 3B, subunit 1—chromosome 2q33.1) mutations have a high prevalence (~80%) in patients with MDS and ring sideroblasts (RS)66 and can also be seen in patients with CMML and RS (<10%).16 In MDS and CMML, these mutations do not influence either the OS or LFS.63, 67 The mutational hot spots for SF3B1 include K700E (~50%), H662Q and K666N.16, 66 Gene expression studies have shown that SF3B1 mutations result in the downregulation of ABCB7 (ATP-binding cassette, sub-family B, member 7), a mitochondrial cassette protein, resulting in the development of RS.68 The gene discussed is SF3B1; the disease is chronic myelomonocytic leukemia.