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Essential thrombocythemia - Genetics Home Reference
Essential thrombocythemia
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Reviewed December 2011
What is essential thrombocythemia?
Essential thrombocythemia is a condition characterized by an increased number of platelets (thrombocythemia). Platelets (thrombocytes) are the blood cells involved in blood clotting.
Abnormal blood clotting (thrombosis) is common in people with essential thrombocythemia and causes many signs and symptoms of this condition; however, some people with essential thrombocythemia have no signs or symptoms. Clots that block blood flow to the brain can cause strokes or temporary stroke-like episodes known as transient ischemic attacks. Thrombosis in the legs can cause leg pain, swelling, or both. In addition, clots can travel to the lungs (pulmonary embolism), blocking blood flow in the lungs and causing chest pain and difficulty breathing (dyspnea).
Another problem in essential thrombocythemia is abnormal bleeding, which occurs more often in people with a very high number of platelets. It is thought that bleeding occurs because a specific protein in the blood that helps with clotting is reduced, although why the protein is reduced is unclear. Affected people may have nosebleeds, bleeding gums, or bleeding in the gastrointestinal tract.
Other signs and symptoms of essential thrombocythemia include an enlarged spleen (splenomegaly); weakness; headaches; or a sensation in the skin of burning, tingling, or prickling. Some people with essential thrombocythemia have episodes of severe pain, redness, and swelling (erythromelalgia), which commonly occur in the hands and feet.
Abnormal blood clotting (thrombosis) is common in people with essential thrombocythemia and causes many signs and symptoms of this condition; however, some people with essential thrombocythemia have no signs or symptoms. Clots that block blood flow to the brain can cause strokes or temporary stroke-like episodes known as transient ischemic attacks. Thrombosis in the legs can cause leg pain, swelling, or both. In addition, clots can travel to the lungs (pulmonary embolism), blocking blood flow in the lungs and causing chest pain and difficulty breathing (dyspnea).
Another problem in essential thrombocythemia is abnormal bleeding, which occurs more often in people with a very high number of platelets. It is thought that bleeding occurs because a specific protein in the blood that helps with clotting is reduced, although why the protein is reduced is unclear. Affected people may have nosebleeds, bleeding gums, or bleeding in the gastrointestinal tract.
Other signs and symptoms of essential thrombocythemia include an enlarged spleen (splenomegaly); weakness; headaches; or a sensation in the skin of burning, tingling, or prickling. Some people with essential thrombocythemia have episodes of severe pain, redness, and swelling (erythromelalgia), which commonly occur in the hands and feet.
How common is essential thrombocythemia?
Essential thrombocythemia affects an estimated 1 to 24 per 1 million people worldwide.
What genes are related to essential thrombocythemia?
Mutations in the JAK2, MPL, THPO, and TET2 genes are associated with essential thrombocythemia. The TET2 gene provides instructions for making a protein whose function is unknown. The JAK2, MPL, and THPO genes provide instructions for making proteins that promote the growth and division (proliferation) of blood cells.
The proteins produced from the JAK2, MPL, and THPO genes are part of a signaling pathway called the JAK/STAT pathway, which transmits chemical signals from outside the cell to the cell's nucleus. The THPO gene provides instructions for making the thrombopoietin protein, and the MPL gene provides instructions for making the thrombopoietin receptor protein. These proteins work together to turn on (activate) the JAK2 protein and the JAK/STAT pathway. Through the JAK/STAT pathway, these proteins promote the proliferation of blood cells, particularly platelets and their precursor cells, megakaryocytes.
Mutations in the JAK2, MPL, and THPO genes that are associated with essential thrombocythemia lead to overactivation of the JAK/STAT pathway. The abnormal activation of JAK/STAT signaling leads to overproduction of megakaryocytes, which results in an increased number of platelets. Excess platelets can cause thrombosis, which leads to many signs and symptoms of essential thrombocythemia.
Although mutations in the TET2 gene have been found in people with essential thrombocythemia, it is unclear what role these gene mutations play in development of the condition.
Many people with essential thrombocythemia do not have a mutation in any of the known genes associated with this condition. Researchers are working to identify other genes that may be involved in the condition.
Read more about the JAK2, MPL, TET2, and THPO genes.
The proteins produced from the JAK2, MPL, and THPO genes are part of a signaling pathway called the JAK/STAT pathway, which transmits chemical signals from outside the cell to the cell's nucleus. The THPO gene provides instructions for making the thrombopoietin protein, and the MPL gene provides instructions for making the thrombopoietin receptor protein. These proteins work together to turn on (activate) the JAK2 protein and the JAK/STAT pathway. Through the JAK/STAT pathway, these proteins promote the proliferation of blood cells, particularly platelets and their precursor cells, megakaryocytes.
Mutations in the JAK2, MPL, and THPO genes that are associated with essential thrombocythemia lead to overactivation of the JAK/STAT pathway. The abnormal activation of JAK/STAT signaling leads to overproduction of megakaryocytes, which results in an increased number of platelets. Excess platelets can cause thrombosis, which leads to many signs and symptoms of essential thrombocythemia.
Although mutations in the TET2 gene have been found in people with essential thrombocythemia, it is unclear what role these gene mutations play in development of the condition.
Many people with essential thrombocythemia do not have a mutation in any of the known genes associated with this condition. Researchers are working to identify other genes that may be involved in the condition.
Read more about the JAK2, MPL, TET2, and THPO genes.
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