User:Portiapliam/Essential thrombocythemia

In ET, megakaryocytes are more sensitive to growth factors. Platelets derived from the abnormal megakaryocytes are activated, which, along with the elevated platelet count, contributes to the likelihood of forming blood clots. The increased possibility of bleeding when the platelet count is over 1 million is due to von Willebrand factor (vWF) sequestration by the increased mass of platelets, leaving insufficient vWF for platelet adhesion. A mutation in the JAK2 kinase (V617F) is present in 40–50% of cases and is diagnostic if present. JAK2 is a member of the Janus kinase family.

In 2013, two groups detected calreticulin mutations in a majority of JAK2-negative/MPL-negative patients with essential thrombocythemia and primary myelofibrosis, which makes CALR mutations the second most common in myeloproliferative neoplasms. All mutations (insertions or deletions) affected the last exon, generating a reading frame shift of the resulting protein, that creates a novel terminal peptide and causes a loss of endoplasmic reticulum KDEL retention signal.

Epidemiology[edit]

The incidence of ET is 0.6-2.5/100,000 per year, the median age at onset is 65–70 years and it is more frequent in females than in males. The incidence in children is 0.09/100,000 per year.

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Edits - added more detail information on the mutations that cause ET

Added more information on Epidemiology

Causes

There are three known genetic mutations that cause ET. The most common genetic mutation is a JAK2 mutation. Roughly 50% of the population of ET patients have this mutation. The JAK 2 gene signals a protein that promotes the growth of cells. The protein is part of a signaling pathway called the JAK/STAT pathway. The JAK2 protein controls the production of blood cells from hematopoietic stem cells which are located in the bone marrow and can eventually become platelets, red blood cells or white blood cells. Specifically in ET, a JAK2 mutation is acquired rather than inherited. The most common JAK2 mutation is V617F which is the replacement of a valine amino acid with phenylalanine amino acid at the 617 position, hence the name V617F. This mutation results in the JAK2 protein constantly being turned on, which leads to the overproduction of abnormal blood cells, in ET it is platelets or megakaryocytes. There is also another JAK2 mutation found in exon 12, however much less common.

There is also a small number of people who have a different mutation called CALR, which is abbreviated from calreticulin. CALR is a protein found in the endoplasmic reticulum (ER). It’s purpose is to mainitan calcium homeostasis and control protein folding. There are 3 parts to CALR including an amino acid domain, a proline rich P-domian, and a carboxyl domain. All of these parts facilitate the function of CALR. CALR mutation is caused by insertions or deletions of amino acids in exon 9 that cause a reading shift, which then leads to the formation of a novel C terminus. There are two common types of CALR mutations, type 1 and type 2. Type 1 mutations are a 52-bp deletion and type 2 mutations are a 5-bp insertion. In type 1 mutations, the negativle charged amino acids in the CALR C terminus are completely eliminated, and in the type 2 mutations, rughly half are eliminated. There are other mutations involving CALR, however these two are the most common.

Lastly, the least common mutation found in patients with ET are MPL mutations. The MPL gene is responsible for making thrombopoeitin receptor proteins which promote the growth and division of cells. This receptor protein is vital in producing platelets. There are various MPL mutation, but most typical are point mutations that cause amino acid changes. The MPL mutation activates the thrombopoeitin receptor despite the absence of the ligand. This causes the constant proliferation of cells.

Epidemiology

There have been reports that approximately 1-2.5 individuals per 100,000 are diagnosed with ET yearly. In the United States, the prevalence is roughly 24 cases per 100,000.