JAK2 V617F Mutation Detection

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1. What causes JAK2 V617F mutation?

The JAK2 V617F mutation is a result of a single change in the DNA nucleotide base pair which causes a substitution of a valine amino acid for a phenylalanine amino acid at the 617 positions on exon 14 within the JAK2 kinase regulatory domain.

2. How common is JAK2 mutation?

The JAK2V617F mutation has a prevalence of 0.1–0.2% in the general population. However, its clinical implications are still unknown for those patients who harbor the mutation without overt signs of a myeloproliferative neoplasm.

3. Can JAK2 mutation be cured?

JAK2 inhibitors and other drugs which are currently used to treat myelofibrosis and other myeloproliferative neoplasms do not cure the disease. Chemotherapy followed by stem cell transplantation is the only available treatment with the potential to cure myelofibrosis.

4. What are the symptoms due to which clinician suspects MPN and orders testing for JAK2 mutation testing?

•     Enlarged spleen (splenomegaly) or liver (hepatomegaly)

•     A blood clot in a vein or artery

•     Heart attack

•     Stroke or transient ischemic attack

•     Bleeding

•     Headache

•     Dizziness

•     Vision problems

•     Numbness

•     Itchiness

•     Gout

•     Kidney stones

•     Fatigue

•     Shortness of breath

•     Weight loss

•     Fever

5. Which disorders are associated with JAK2 mutations?

The bone marrow disorders which are 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 as follows:

• 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

6.  How is the test for the mutation used?

The JAK2 mutation test may be used, along with other tests, which may be the CALR mutation and MPL mutation testing, to help diagnose bone marrow disorders that lead to the production of too many blood cells. These disorders are known as myeloproliferative neoplasms (MPNs).

The JAK2 mutation test is typically ordered as a follow-up test if a person has a significantly increased hemoglobin, hematocrit, red blood cells and/or platelet count and the clinician suspects that the patient may have an MPN, especially polycythemia vera (PV), essential thrombocythemia (ET), or primary myelofibrosis (PMF).

The primary genetic test for JAK2 mutations that lead to MPNs is JAK2 V617F, named for a mutation at a specific location in the JAK2 gene. It is typically ordered first. If it is negative, then tests for other mutations in the JAK2 gene that are also associated with MPNs, such as JAK2 exon 12, may be used to help make a diagnosis.

7.  Are there any genetic mutations associated with MPNS?

Yes, calreticulin (CALR) gene mutations (exon 9) are detected in 20-25% of adult patients with essential thrombocythemia (ET) and 25-30% of adult patients with primary myelofibrosis (PMF). In addition, mutations in the myeloproliferative leukemia (MPL) gene are seen in 2-5% of adult ET patients and 3-5% of adult PMF patients, but not with polycythemia vera (PV). PV, ET and PMF are all rare in children and adolescents and although mutations might not be as common as in adults with these same diseases, not much is known. Genetic testing is also sometimes used to check for the presence or absence of a Philadelphia (Ph') chromosome or a BCR-ABL1 translocation in a person suspected of having chronic myeloid leukemia.

8.  Is there any reason to repeat the JAK2 mutation test?

A clinician may repeat this test if the test result is found negative and the clinician feels that the mutation may have been missed. One reason it might be negative is that the proportion of patient’s cells that have the JAK2 V617F mutation may be low. The test is not nationally standardized currently, so the sensitivity of the test may vary somewhat from laboratory to laboratory. A second test done at a later time and/or sent to a different laboratory may detect the JAK2 V617F mutation if it is present. Also, some clinicians may order a quantitative test periodically to monitor the change in the number of cells with the JAK2 V617F mutation over time. Results from repeated quantitative tests may be helpful in monitoring the effectiveness of treatment if ongoing research shows that the JAK2 gene is an appropriate target for MPN therapies.

9.  Are these mutations present since birth?

These mutations are not present since birth, but develop it instead in their bone marrow cells sometime later in life.

10.  Does everyone have this JAK2 gene?

JAK2 mutation should not be present in the normal general population; it is a sign of an underlying hematologic condition but not it is not specific. It is more common in patients with polycythemia vera or myelofibrosis. It also can be seen in those with myelodysplastic syndromes (MDS) and leukemias.

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