Myelodysplastic syndromes (MDS) are disorders of bone marrow characterized by hypercellularity, dysplastic (abnormal) maturation, and often an excess number of blasts. Anemia and often neutropenia and thrombocytopenia are present. A high percentage of cases progress to acute leukemia (usually AML), and for this reason, MDS has been called preleukemia. Categories include:
- refractory anemia (RA) with fewer than 5% blasts,
- refractory anemia with ringed sideroblasts (RARS),
- refractory anemia with excess blasts (RAEB)containing up to 20% blasts,
- RAEB in transformation to acute leukemia (RAEB-T),
- and chronic myelomonocytic leukemia (CMML). MDS may be primary or secondary (therapy-related).
MDS is more common in older adults but can be seen at any age.
Two rare and specific forms of MDS have the name of the associated chromosome abnormality.
Monosomy 7 syndrome of childhood is characterized by occurrence in young children, anemia, thrombocytopenia, and leukocytosis including monocytosis. Within the marrow, there may be dysplastic changes and low numbers of megakayocytes.
5q- syndrome is characterized by occurrence is adults with a higher incidence in females, prolonged clinical course, moderate to severe anemia, and normal to elevated leukocyte and platelet counts. In the marrow, there are clusters of abnormal megakaryocytes with round nuclei and there may be an excess of myeloblasts. These adults have no history of previous exposure to radiotherapy or chemotherapy.
It should be noted that monosomy 7 and 5q- are chromosome abnormalities that commonly occur in other forms of primary or secondary MDS and AML in addition to the specific monosomy 7 and 5q- syndromes.
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University of Wisconsin Cytogenetic Services