Within the genetically defined group, MDS with isolated del(5q) was retained from earlier classifications, while two newly recognized entities were added: MDS with biallelic TP53 inactivation, which superimposes over several prior subtypes, and MDS with SF3B1 mutation, which overlaps with the former category of MDS with ring sideroblasts, as well as partially with unilineage and multilineage dysplasia subtypes. The gene discussed is SF3B1; the disease is myelodysplastic syndrome.