Aplastic Anemia & Myelodysplasia Association of Canada (AAMAC)
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What Are Aplastic Anemia and Myelodysplastic Syndrome and PNH?

Aplastic anemia is a rare but extremely serious disorder that results when the marrow fails to produce blood cells. Aplastic anemia may be either acquired or inherited.

Myelodysplasia is similar to aplastic anemia in that production of blood cells is decreased; however, the blood cells which are produced in myelodysplasia may not function properly. Aplastic anemia patients who do not receive a bone marrow transplant may go on to develop myelodysplasia which, in turn, can progress to leukemia.

Another related disease, Paroxysmal nocturnal hemoglobinuria (PNH), is caused by a mutation of the stem cells in the marrow. These mutated stem cells produce defective platelets that can form dangerous clots in the body and defective red blood cells which break down easily because they lack the protective proteins necessary for the cells' survival.

How Common?

Aplastic anemia is a rare disease. It is estimated that there are 2 to 12 new cases per million population per year. It occurs in both adults and children. Myelodysplasia is more common, with the majority of patients being over the age of 50.

How are Aplastic Anemia and Myelodysplasia Treated?

Treatment depends upon the patient's age, the severity of the disease, and the availability of a Human Leukocyte Antigen (HLA) matched donor.

The Function of Bone Marrow

The central portion of bones is filled with a spongy red tissue called bone marrow. The bone marrow is essentially a factory producing the cells of the blood: red cells that carry oxygen from the lungs to all areas of the body; white cells that fight infection by attacking and destroying germs, and platelet cells (platelets) that control bleeding by forming blood clots in areas of injury. Continuous production of blood cells is necessary all through life because each cell has a finite life span once it leaves the bone marrow and enters the blood:

  • red cells: 120 days;
  • platelets: 8 - 10 days;
  • white cells: one day or less.

Healthy bone marrow is a superb blood cell factory and supplies as many cells as needed, increasing production of red cells and platelets when bleeding occurs and of white cells when infection threatens. When bone marrow cell production fails, normal levels of red cells, white cells, and platelets begin to fail. Bruising, bleeding, infection, tiredness, pallor, and other symptoms of anemia may develop.

Causes of Aplastic Anemia and Myelodysplasia

Although a congenital chromosomal abnormality may predispose one to develop inherited aplastic anemia, the medical community does not know the cause of most cases of acquired aplastic anemia. Certain toxic chemicals, medications, viral infections and radiation exposure appear to cause both myelodysplasia and aplastic anemia, but millions of people with exposure to the same factors do not develop either disease.


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