Polycythemia vera, the most common form of polycythemia, is not directly inherited. It’s caused by a mutation that develops spontaneously in bone marrow cells during a person’s lifetime, not one passed down from parents. However, rare hereditary forms of polycythemia do exist, and even with polycythemia vera, your genetic background can raise your susceptibility.
The distinction matters because hereditary and acquired forms behave differently, carry different risks, and require different monitoring. Here’s how to sort them out.
Polycythemia Vera Is Acquired, Not Inherited
About 95% of people with polycythemia vera carry a specific mutation called JAK2 V617F. This mutation is somatic, meaning it appears in bone marrow cells at some point during life rather than being present at birth. Studies of families with multiple members affected by blood cancers have found no evidence that the JAK2 V617F mutation existed in the germline (inherited DNA) of patients who carried it in their tumor cells. The mutation is a later event, not something coded into every cell from conception.
That said, the story isn’t quite that simple. Research has identified a particular inherited version of the JAK2 gene (a specific haplotype) that makes the somatic mutation more likely to occur on top of it. This inherited predisposition may account for as much as 50% of the risk to first-degree relatives. A large Swedish study of over 24,000 first-degree relatives of patients with myeloproliferative neoplasms found that relatives had a 5.7-fold increased risk of developing polycythemia vera compared to the general population. So while you don’t inherit polycythemia vera itself, you can inherit a genetic landscape that makes it more likely.
Polycythemia vera has a prevalence of roughly 44 to 57 per 100,000 people in the United States. It’s classified as a myeloproliferative neoplasm, a type of slow-growing blood cancer, and carries risks of clonal evolution into more serious conditions over time.
Hereditary Forms: Familial Erythrocytosis
True hereditary polycythemia, known as familial erythrocytosis, is a group of rare congenital disorders where gene mutations present from birth cause the body to overproduce red blood cells. At least eight types have been identified, each tied to a different gene. These conditions are far less common than polycythemia vera, and unlike PV, they don’t carry a risk of transforming into leukemia or other blood cancers.
The types fall into three broad categories based on what the mutated gene disrupts:
- Hypersensitivity to the red-blood-cell growth signal (type 1): Mutations in the EPOR gene make red blood cell precursors overreact to erythropoietin, the hormone that tells the body to produce more red blood cells. This is autosomal dominant, meaning one copy of the mutated gene from one parent is enough to cause the condition. More than 28 different EPOR variants have been identified.
- Defective oxygen sensing (types 2 through 5): Mutations in genes like VHL, EGLN1, EPAS1, and EPO disrupt the body’s ability to accurately detect oxygen levels. The body essentially behaves as though it’s not getting enough oxygen, even when it is, and ramps up red blood cell production in response.
- Hemoglobin that holds oxygen too tightly (types 6 through 8): Mutations in hemoglobin genes (HBB, HBA1, HBA2) or a related enzyme (BPGM) cause hemoglobin to bind oxygen more firmly than normal. Because the hemoglobin doesn’t release oxygen to tissues efficiently, the body compensates by making more red blood cells.
Chuvash Polycythemia: A Well-Studied Example
The best-known hereditary form is Chuvash polycythemia, caused by a specific mutation (R200W) in the VHL gene. It was the first recognized congenital disorder of augmented oxygen sensing. Unlike type 1, this condition is autosomal recessive: you need two copies of the mutated gene, one from each parent, to develop it.
The VHL protein normally helps the body break down a molecule called HIF (hypoxia-inducible factor) when oxygen levels are adequate. When VHL doesn’t work properly, HIF accumulates as if the body were oxygen-starved, driving up erythropoietin production and, with it, red blood cell counts. People homozygous for this mutation have elevated HIF levels, increased red cell mass, a tendency toward blood clots, and higher early mortality.
Chuvash polycythemia is most common in the Chuvash Republic of Russia, where about 200 cases have been recognized, but the same mutation appears in people of various ethnic backgrounds worldwide. Genetic analysis suggests it originated in a single ancient founder before human populations diverged.
How the Two Types Are Told Apart
The clinical picture differs in important ways. Polycythemia vera typically appears in middle age or later, involves abnormalities beyond just red blood cells (white blood cell and platelet counts often rise too), and tests positive for the JAK2 mutation. Hereditary erythrocytosis, by contrast, is present from birth, produces isolated elevations in red blood cells without affecting other blood cell lines, and tests negative for JAK2.
Doctors typically rule out polycythemia vera first because it’s far more common. If JAK2 testing comes back negative and secondary causes like chronic lung disease, sleep apnea, smoking, or high-altitude living have been excluded, hereditary erythrocytosis becomes a consideration. A family history of elevated hemoglobin strengthens the suspicion, though new mutations can arise spontaneously in an individual without any family history.
Specialized genetic testing panels now assess 24 or more genes associated with hereditary erythrocytosis. These panels are typically recommended for people with lifelong, unexplained increases in red blood cell counts who’ve already tested negative for JAK2 and for high-oxygen-affinity hemoglobin variants. Establishing a specific genetic diagnosis matters because different genes carry different health risks and call for different monitoring strategies.
Common Non-Genetic Causes Worth Ruling Out
Before considering hereditary causes, it’s worth noting that the most frequent reasons for a high red blood cell count aren’t genetic at all. Chronic obstructive pulmonary disease, obstructive sleep apnea, obesity-related breathing problems, heavy smoking, and living at high altitude all reduce oxygen delivery to tissues, prompting the body to compensate with more red blood cells. Even dehydration can make red blood cell counts appear elevated by reducing the fluid portion of blood.
Less commonly, certain tumors (kidney, liver, brain) can produce erythropoietin independently, and some medications including testosterone can stimulate red blood cell production. These acquired, secondary causes are believed to be considerably more common than both polycythemia vera and hereditary erythrocytosis combined, making them the first thing to investigate when blood counts come back high.
What Runs in Families: A Summary
If a close relative has polycythemia vera, your risk of developing it is roughly five to seven times higher than the general population’s. That elevated risk is real but still translates to a low absolute probability, since PV affects fewer than 1 in 1,700 people to begin with. The inherited susceptibility sits in the JAK2 gene region itself, though the disease-causing mutation must still arise independently in your bone marrow cells.
If a relative has hereditary erythrocytosis, the inheritance pattern depends on the specific gene involved. Type 1 (EPOR mutations) follows a dominant pattern, so each child of an affected parent has a 50% chance of inheriting it. Chuvash polycythemia and some other oxygen-sensing types are recessive, requiring both parents to carry the mutation. Hemoglobin-related types are typically dominant. Genetic counseling can clarify the specific risk for your family based on which gene is involved.