SF3B1 and myelodysplastic syndrome with single lineage dysplasia: They have been identified in approximately 60% of all MDS cases (2), with mutations in splicing factor 3B, subunit 1 (SF3B1) observed in 80–90% of cases with the refractory anemia with ringed sideroblast (RARS) subtype (1, 3, 83, 84).