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JAK2 Mutation

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Also known as: Janus Kinase 2
Formal name: JAK2 V617F; JAK2 Exon 12 Mutation

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The Test Sample

What is being tested?

The Janus Kinase 2 gene, called JAK2 for short, provides instructions to cells for making the JAK2 protein. This protein promotes cell growth and division and is especially important for controlling blood cell production within the bone marrow. This test looks for mutations in JAK2 that are associated with bone marrow disorders caused by the production of too many blood cells.

The bone marrow disorders caused by JAK2 mutations are known as myeloproliferative neoplasms (MPNs) in which the bone marrow produces too many white blood cells, red blood cells, and/or platelets. Some of the MPNs most commonly associated with JAK2 mutations are:

  • Polycythemia vera (PV)—the bone marrow makes too many red blood cells
  • Essential thrombocythemia (ET)—there are too many platelet-producing cells (megakaryocytes) in the bone marrow
  • Primary myelofibrosis (PMF), also known as chronic idiopathic myelofibrosis or agnogenic myeloid metaplasia—there are too many platelet-producing cells and cells that produce scar tissue in the bone marrow

The primary JAK2 test is JAK2 V617F, named for a mutation at a specific location in the JAK2 gene. JAK2 V617F mutation is acquired as opposed to inherited and results in the change of a single DNA nucleotide base pair. In JAK2, this kind of mutation, called a point mutation, replaces the normal amino acid valine (abbreviated V) with phenylalanine (abbreviated F). This amino acid change results in a JAK2 protein that is constantly "on," leading to uncontrolled blood cell production.

Other mutations in the JAK2 gene are also associated with MPNs. Over 50 different mutations have been identified. There are tests available to detect mutations in JAK2 exon 12 and to identify other non-V617F mutations.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes a bone marrow aspiration and biopsy may be done to collect a sample for testing.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.