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Ancestor membership does not transfer phenotype values between groups.","importantHtml":""},"sections":[{"bodyHtml":"<p>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.</p><p>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.</p><p>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.</p><p class=\"section-source\"><a href=\"https://medlineplus.gov/genetics/condition/polycythemia-vera/#causes\">MedlinePlus Genetics: Causes</a></p>","key":"forms","title":"What causes Polycythemia vera?"},{"bodyHtml":"<p>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).</p><p class=\"section-source\">Source: <a href=\"https://medlineplus.gov/genetics/condition/polycythemia-vera\">MedlinePlus Genetics</a></p>","key":"overview","title":"Condition overview"}],"sharedSources":[],"slug":"polycythemia-vera","sourceDocuments":[{"name":"Polycythemia vera","reviewed":"2010-05","sections":{"causes":{"fetchedAt":"2026-10-20T20:24:17.714667+00:00","label":"Causes","pageSha256":"d9781d1c2eb3507d05e16b155dd0a85907417579c3f81c04208a6a2abbcf535d","sourceUrl":"https://medlineplus.gov/genetics/condition/polycythemia-vera/#causes","status":"available"}},"source_release":"2026-10-01","url":"https://medlineplus.gov/genetics/condition/polycythemia-vera"}],"sourceNote":"MedlinePlus descriptions and Causes; original HPO annotations.","takeawayHtml":"Cause explanations are from MedlinePlus Genetics. Feature values below retain their original sources and patient groups.","title":"Polycythemia vera"},"schemaVersion":1}