Polycythemia vera is a condition characterized by an increased number of red blood cells in the bloodstream. Affected individuals may also have excess white blood cells and blood clotting cells called platelets. These extra cells and platelets cause the blood to be thicker than normal. As a result, abnormal blood clots are more likely to form and block the flow of blood through arteries and veins. Individuals with polycythemia vera have an increased risk of deep vein thrombosis (DVT), a type of blood clot that occurs in the deep veins of the arms or legs. If a DVT travels through the bloodstream and lodges in the lungs, it can cause a life-threatening clot known as a pulmonary embolism (PE). Affected individuals also have an increased risk of heart attack and stroke caused by blood clots in the heart and brain.

Polycythemia vera typically develops in adulthood, around age 60, although in rare cases it occurs in children and young adults. This condition may not cause any symptoms in its early stages. Some people with polycythemia vera experience headaches, dizziness, ringing in the ears (tinnitus), impaired vision, or itchy skin. Affected individuals frequently have reddened skin because of the extra red blood cells. Other complications of polycythemia vera include an enlarged spleen (splenomegaly), stomach ulcers, gout (a form of arthritis caused by a buildup of uric acid in the joints), heart disease, and cancer of blood-forming cells (leukemia).

The prevalence of polycythemia vera varies worldwide. The condition affects an estimated 44 to 57 per 100,000 individuals in the United States. For unknown reasons, men develop polycythemia vera more frequently than women.

Mutations in the JAK2 and TET2 genes are associated with polycythemia vera. Although it remains unclear exactly what initiates polycythemia vera, researchers believe that it begins when mutations occur in the DNA of a hematopoietic stem cell. These stem cells are located in the bone marrow and have the potential to develop into red blood cells, white blood cells, and platelets. JAK2 gene mutations seem to be particularly important for the development of polycythemia vera, as nearly all affected individuals have a mutation in this gene. The JAK2 gene provides instructions for making a protein that promotes the growth and division (proliferation) of cells. The JAK2 protein is especially important for controlling the production of blood cells from hematopoietic stem cells.

JAK2 gene mutations result in the production of a JAK2 protein that is constantly turned on (constitutively activated), which increases production of blood cells and prolongs their survival. With so many extra cells in the bloodstream, abnormal blood clots are more likely to form. Thicker blood also flows more slowly throughout the body, which prevents organs from receiving enough oxygen. Many of the signs and symptoms of polycythemia vera are related to a shortage of oxygen in body tissues.

The function of the TET2 gene is unknown. Although mutations in the TET2 gene have been found in approximately 16 percent of people with polycythemia vera, it is unclear what role these mutations play in the development of the condition.

Genetic Testing Information

• Genetic Testing Registry: Acquired polycythemia vera

Genetic and Rare Diseases Information Center

• Polycythemia vera

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Clinical Trials

• ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

• POLYCYTHEMIA VERA; PV

Scientific Articles on PubMed

• PubMed

• Cario H, McMullin MF, Pahl HL. Clinical and hematological presentation of children and adolescents with polycythemia vera. Ann Hematol. 2009 Aug;88(8):713-9. doi: 10.1007/s00277-009-0758-y. Epub 2009 May 26. Citation on PubMed or Free article on PubMed Central
• Delhommeau F, Jeziorowska D, Marzac C, Casadevall N. Molecular aspects of myeloproliferative neoplasms. Int J Hematol. 2010 Mar;91(2):165-73. doi: 10.1007/s12185-010-0530-z. Epub 2010 Feb 27. Citation on PubMed
• Gangat N, Strand J, Lasho TL, Finke CM, Knudson RA, Pardanani A, Li CY, Ketterling RP, Tefferi A. Cytogenetic studies at diagnosis in polycythemia vera: clinical and JAK2V617F allele burden correlates. Eur J Haematol. 2008 Mar;80(3):197-200. doi: 10.1111/j.1600-0609.2007.01003.x. Epub 2007 Dec 7. Citation on PubMed
• Landolfi R, Nicolazzi MA, Porfidia A, Di Gennaro L. Polycythemia vera. Intern Emerg Med. 2010 Oct;5(5):375-84. doi: 10.1007/s11739-010-0369-6. Epub 2010 Mar 16. Citation on PubMed
• Mehta J, Wang H, Iqbal SU, Mesa R. Epidemiology of myeloproliferative neoplasms in the United States. Leuk Lymphoma. 2014 Mar;55(3):595-600. doi: 10.3109/10428194.2013.813500. Epub 2013 Jul 29. Citation on PubMed
• Tefferi A. Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1. Leukemia. 2010 Jun;24(6):1128-38. doi: 10.1038/leu.2010.69. Epub 2010 Apr 29. Citation on PubMed or Free article on PubMed Central
• Thiele J, Kvasnicka HM. The 2008 WHO diagnostic criteria for polycythemia vera, essential thrombocythemia, and primary myelofibrosis. Curr Hematol Malig Rep. 2009 Jan;4(1):33-40. doi: 10.1007/s11899-009-0005-6. Citation on PubMed