Essential thrombocytosis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Pathophysiology
As defined by WHO, ET is a clonal proliferation of pluripotent stem cells with predominantly megakaryocytic differentiation.[1] Recent studies have shown that other cell lineages can also be affected to some degree, resulting in their respective cell proliferation. The megakaryocyte proliferation in the bone marrow results in the abnormally increased number of platelets into the circulation. Thrombopoietin(TPO) is a hormone produced predominantly by the liver, bone marrow and kidney, that regulates the stimulation,production and proliferation of megakaryocytes. Once thrombopoietin binds to the TPO receptors on the megakaryocytes, it is destroyed thus making the megakaryocyte unavailable for further hormonal interaction.[2] Given the higher platelet count, ET should be presenting with lower thrombopoietin levels. But there is a paradoxical increase in the free circulating levels of thrombopoietin as the abnormal platelets in ET have defective TPO receptors that do not allow proper binding of thrombopoietin. Platelets contain different types of granules alpha(contain P-selectin, platelet factor 4, transforming growth factor-β1, platelet-derived growth factor, fibronectin, B-thromboglobulin, vWF, fibrinogen, and coagulation factors V and XIII), Delta(δ) or Dense granules(contain ADP or ATP, calcium, and serotonin), Gamma(γ) and Lambda(λ) granules. With defective granules in ET, there is a deficiency in clotting factors like fibrinogen and von Willebrand(vWF) that impair the process of aggregation. On the other hand patients with secondary or reactive thrombocytosis have a normal platelet activity with no defects in aggregation.
The pathologic basis for this disease is unknown. However, essential thrombocytosis resembles polycythemia vera in that cells of the megakaryocytic series are more sensitive to growth factors. Platelets derived from the abnormal megakaryocytes do not function properly, which contributes to the clinical features of bleeding and thrombosis.
In 2005, a mutation in the JAK2 kinase (V617F) was found by multiple research groups [3][4] [5] to be associated with essential thrombocytosis in around 30% of cases. JAK2 is a member of the Janus kinase family. This mutation may be helpful in making a diagnosis or as a target for future therapy.
References
- ↑ Sanchez S, Ewton A (2006). "Essential thrombocythemia: a review of diagnostic and pathologic features". Arch Pathol Lab Med. 130 (8): 1144–50. doi:10.1043/1543-2165(2006)130[1144:ET]2.0.CO;2. PMID 16879015 PMID: 16879015 Check
|pmid=value (help). - ↑ Thrombopoietin. Wikipedia. https://en.wikipedia.org/wiki/Thrombopoietin#Function_and_regulation. Accessed on Novenber 3rd,2015.
- ↑ Kralovics R, Passamonti F, Buser AS, Teo SS; et al. (2005 Apr 28). "A gain-of-function mutation of JAK2 in myeloproliferative disorders". N Engl J Med. 352 (17): 1779–90. Check date values in:
|date=(help) - ↑ Baxter EJ et al. Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative disorders. Lancet. 2005;365:1054-61. PMID 15781101
- ↑ Levine RL et al. Activating mutation in the tyrosine kinase JAK2 in polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis. Cancer Cell. 2005;7:387-97. PMID 15837627