Myelodysplastic syndromes (MDS) are a group of conditions in which bone marrow stem cells produce abnormal blood cells, including erythrocytes (red blood cells), leukocytes (white blood cells), and platelets. The abnormal cells do not mature or function properly, and are often destroyed either before they leave the bone marrow or shortly after they enter the bloodstream.
Patients with MDS often have too many young, immature blood-making cells in the bone marrow; when more than 20 percent of the bone marrow is taken up with these cells, the disease is said to have transformed into acute myeloid leukemia (AML). Because of the difficulty in making good-quality blood cells of different types, MDS patients are often anemic and fatigued. They may also bruise or bleed easily due to low platelet counts, or have frequent fevers or infections as a result of too few infection-fighting cells. MDS turns into AML in about 30 percent of cases.
About 12,000 new MDS cases are diagnosed each year in the United States. Most patients are men, and about 80 percent of all patients are older than 60.
Normal Blood Cells
Most blood cells develop in the marrow, the soft material at the center of bones. Bone marrow contains hematopoietic stem cells, which can transform into different kinds of blood cells, depending on what kind your body needs at a particular time. When cells grow old or are damaged, they die, and the hematopoietic stem cells replace them.
- Stem cells: mature into either myeloid stem cells or lymphoid stem cells.
- A myeloid stem cell matures into a myeloid blast. The blast can form a red blood cell, platelets, or one of several types of white blood cells.
- A lymphoid stem cell matures into a lymphoid blast. The blast can form one of several types of white blood cells, such as B-cells or T-cells.
Each type of blood cell has a special job:
- White blood cells help fight infection. There are several types of white blood cells.
- Red blood cells carry oxygen to tissues throughout the body.
- Platelets help form blood clots to control bleeding.
In a person with MDS, the bone marrow makes immature blood cells (blasts) that do not work properly and remain clustered in the bone marrow.
Some MDS patients have an unusual feature — the presence of immature red blood cells that contain too many iron granules, called sideroblasts, that form in a ring.
Types of MDS
MDS includes many subtypes that are classified according to the number of blasts in the bone marrow, and the presence of ringed sideroblasts and specific chromosome abnormalities in the blood and bone marrow. A higher percentage of blasts indicates a greater chance of developing AML.
MDS subtypes include:
- Refractory anemia (RA): About 8-15 percent of MDS cases involve refractory anemia. MDS patients with refractory anemia have low numbers of red blood cells, which have an abnormal appearance. The number of immature cells (called blasts) in the bone marrow is normal (less than 5 percent). A small percentage (less than 15 percent) of the red blood cells in the bone marrow may contain ringed sideroblasts.
- Refractory anemia with ringed sideroblasts (RARS): Between 1.5-11 percent of MDS cases involve RARS. RARS has the same characteristics as refractory anemia (above), except that the number of ringed sideroblasts exceeds 15 percent.
- Refractory anemia with excess blasts-1 (RAEB-1): In RAEB-1, there are not enough of one of the three types of blood cells, and those cells can appear abnormal. The number of blasts is greater than 5 percent, but less than 10 percent. About 18-21 percent of MDS cases involve RAEB-1.
- Refractory anemia with excess blasts-2 (RAEB-2): This is the same condition as RAEB-1, except that the number of blasts is greater than 10 percent but less than 20 percent. RAEB-2 accounts for about 15-18 percent of MDS cases.
- Myelodysplastic syndrome, unclassified (MDS-U): Patients with MDS-U do not have enough of one of the three cell types, and abnormal white cell and platelet progenitor cells (a stage between stem cells and mature cells) are present. The number of blasts is less than 5 percent. Between 0-18 percent of all MDS cases involve MDS-U.
- MDS associated with isolated deletion (5q): Patients have only refractory anemia (anemia that does not respond to treatment), but part of a specific chromosome — chromosome 5 — is missing.
The next two types of MDS (variations of RCMD) account for between 32-39 percent of all cases of MDS:
- Refractory cytopenia with multilineage dysplasia (RCMD): In RCMD, there are not enough of at least two of the three different types of blood cells (red blood cells, white blood cells or platelets), and at least two of the blood cell types also have an abnormal appearance. The number of blasts is less than 5 percent and the number of ringed sideroblasts is less than 15 percent.
- Refractory cytopenia with multilineage dysplasia (RCMD) with ringed sideroblasts: This condition is the same as RCMD, except that the number of ringed sideroblasts is higher than 15 percent.
The symptoms of MDS are caused by not having enough healthy blood cells in the bloodstream. They can include:
- Feeling fatigued
- Fever and frequent infections
- Poor healing of minor cuts
- Easy bleeding or bruising
- Paleness, shortness of breath
In severe MDS, infection or uncontrolled bleeding can be life-threatening.