Myelodysplastic syndromes are characterized by ineffective and dysplastic hematopoiesis and include the following: Refractory anemia: Anemia with reticulocytopenia; normal or hypercellular marrow with erythroid hyperplasia, and dyserythropoiesis; blasts ≤ 5% of nucleated marrow cells Refractory anemia with ringed sideroblasts: Same as refractory anemia with reticulocytopenia, except that ringed sideroblasts are > 15% of nucleated marrow cells Refractory cytopenia with multilineage dysplasia: Cytopenia not restricted to red cells; prominent dysplasia of white cell precursors and megakaryocytes Refractory cytopenia with multilineage dysplasia and ringed sideroblasts: With ringed sideroblasts that are > 15% of nucleated marrow cells Refractory anemia with excess blasts (RAEB): Cytopenia of ≥ 2 cell lines with morphologic abnormalities of hematopoietic cells; hypercellular marrow with dyserythropoiesis and dysgranulopoiesis; blasts 5 to 9% (RAEB-I) or 10 to 19% (RAEB-II) of nucleated marrow cells Myelodysplastic syndrome, unclassified: MDS that does not fall into any defined category MDS with isolated del (5q): Typically severe anemia and thrombocytosis, with deletion of the long arm of chromosome 5 Chronic myelomonocytic leukemia (CMML) and juvenile myelomonocytic leukemia (JMML): Mixed myelodysplastic / myeloproliferative neoplasms; absolute monocytosis (> 1000 / mcL [> 1/L]) in blood; significant increase in marrow monocyte precursors Chronic neutrophilic leukemia: Characterized by neutrophilia and absence of the Philadelphia chromosome and the BCR-ABL1 fusion gene The etiology of myelodysplastic syndrome is unknown.