There are subtle differences in how the two systems designate MDS with SF3B1 mutation, in that the WHO also recognizes cases with increased (≥15%) ring sideroblasts without SF3B1 mutation as a continuum of the SF3B1 mutated category, allowing for the use of MDS with RS as an alternative designation in order to account for cases with similar biology driven by similar genetic lesions such as those involving other splicing factors, whereas the ICC classifies such cases as MDS, not otherwise specified. The gene discussed is SF3B1; the disease is myelodysplastic syndrome.