Polycythemia vera occurs when a mutation in a bone marrow cell causes a problem with blood cell production. Normally, your body carefully regulates the number of each of the three types of blood cells you have. But in polycythemia vera, the mechanism your body uses to control the production of blood cells becomes damaged, and your bone marrow makes too many of some blood cells.

The mutation that causes polycythemia vera is thought to affect a protein switch that tells the cells to grow. Specifically, it's a mutation in the protein JAK2 (the JAK2 V617F mutation). Most people with polycythemia vera have this mutation. There are other mutations found in people with polycythemia vera, but it's not yet known what role these mutations play in the development of the disease or what the implications of these mutations might mean for treating the disease.

It's not clear what causes the mutations seen in polycythemia vera. Researchers believe the mutation occurs after conception — meaning that your mother and father don't have it — so it's acquired, rather than inherited from a parent.

Apr. 10, 2014