Types of MDS

Myelodysplastic syndromes (MDS) is not a single disease. It is a group of diseases, and each disease involves faulty blood cell production.1 In MDS, many of the blood cells produced in the bone marrow fail to mature. These immature cells are called blasts, and the number of them in the bone marrow is an important indicator of the type of MDS a person has.1

Another important indicator in determining the type of MDS is the number of blood cell types, or lines, that are abnormal. There are three blood cell lines: red blood cells, white blood cells and platelets, and when a person has an abnormally low number of cells in any cell line it is called a cytopenia. In general, the more cytopenias a person with MDS has, the more serious the disease is.1

When a person has red blood cell cytopenia, it is called anemia (low red blood cell count), and the main symptom is fatigue. White blood cell cytopenia, or low white blood cell count, is called neutropenia, and its main symptom is an increased risk of infection. When a person has a low platelet count, the cytopenia is called thrombocytopenia, and it makes the person more likely to bruise or bleed easily.1

Many researchers and doctors use a traditional classification tool called the French-American-British (FAB) system to classify the five main types of MDS:

• Refractory anemia (RA): With RA, there is cytopenia of at least one type of cell, usually the red blood cells. There are less than 1% blasts in the blood and less than 5% blasts in the bone marrow.1
• Refractory anemia with ringed sideroblasts (RARS): This type of MDS has the same features as RA, but more than 15% blasts in the bone marrow are "ringed sideroblasts". In RARS, the developing red blood cells in the bone marrow cannot use the iron necessary to produce hemoglobin (the part of the red blood cell that carries oxygen). Iron forms a visible dark ring in the developing red blood cell, leading to the name "ringed sideroblast".1
• Refractory anemia with excess blasts (RAEB): With RAEB, there is cytopenia of at least two types of blood cells. There are less than 5% of blasts in the blood and between 5% and 20% of blasts in the bone marrow.1
• Refractory anemia with excess blasts in transformation (RAEB-t): This type of MDS has cytopenia in at least two types of blood cells. There are more than 5% of blasts in the blood and between 21% and 29% of blasts in the bone marrow.1
• Chronic Myelomonocytic Leukemia (CMML): With CMML, there is an excess of monocytes in the blood. There are less than 5% of blasts in the blood and less than 20% of blasts in the bone marrow.1 Monocytes, a type of white blood cell, multiply in abnormal quantities.

Talk to your health care team for more details on the different types of MDS.

Visit other pages in this section to learn more about MDS, including the following:

• Symptoms of MDS
• Impact of MDS on Quality of Life