Final answer:
Patients with polycythemia vera have a mutation in erythropoietin (EPO), a hormone that stimulates red blood cell production in the bone marrow. Synthetic EPO is used both as a banned substance by athletes to enhance performance, and medically to treat anemia.
Step-by-step explanation:
Virtually all patients with polycythemia vera have a mutation in erythropoietin (EPO), a non-receptor (cytoplasmic) tyrosine kinase associated with the EPO receptor (constitutive activation). EPO is a glycoprotein hormone secreted by the kidneys in response to low oxygen levels. It stimulates the production of red blood cells in the bone marrow. Some athletes use synthetic EPO as a performance-enhancing drug to increase their red blood cell counts and improve oxygen delivery, but it is also used medically to treat certain types of anemia.