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Essential Thrombocythemia

Causes and Risk Factors

For most people who have essential thrombocythemia (ET), there are no obvious reasons (risk factors) why they developed the disease.

Doctors don't fully understand what causes ET. About half of all patients with ET have a mutation (change) of the JAK2 (Janus kinase 2) gene. This mutated gene may play a role in ET's onset. However, researchers are still studying its precise role as the cause of the disease.

How Does ET Develop?

ET results from a mutation in a stem cell in the bone marrow, which leads to uncontrolled blood cell production, especially platelets. Because stem cells form red cells, white cells and platelets, any combination of these cell lines can be affected and usually each cell line is affected to some degree.

In ET, there is mainly an overproduction of platelet-forming cells, called "megakaryocytes," in the marrow. This results in the release of too many platelets into the blood. A platelet is a small blood cell. Its function is to start the process of forming a plug (clot) in response to blood vessel injury in order to prevent or minimize bleeding. When platelets are present in very high numbers they may not function normally and may cause a blockage in blood vessels, known as a  "thrombus." Less often, a high number of platelets can also cause bleeding problems.

Another word for platelet is "thrombocyte." The term "thrombocythemia" means an excess of platelets in the blood. The term "essential" indicates that the increase in platelets is an innate problem of the blood cell production in the bone marrow. "Secondary thrombocytosis" is the term for a condition that results in very high platelet counts in the blood in reaction to another problem in the patient's body, such as inflammatory disease, removal of the spleen, or iron deficiency in adults. A patient with secondary, or reactive, thrombocytosis should have a return to normal platelet count in the blood once the primary problem is treated successfully.

Source: Essential Thrombocythemia. Reviewed by Srdan Verstovsek, MD, PhD.

last updated on Thursday, October 25, 2012
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