what is wrong when you have too many red blood cells
If you have PV, your bone marrow makes too many red blood cells. It also can make too many white blood cells and platelets. A mutation, or change, in the body's JAK2 gene is the major cause of PV.This gene makes a protein that helps the body produce blood cells.What causes the change in the JAK2 gene isn't known.t also can make too many white blood cells and platelets. A mutation, or change, in the body's JAK2 gene is the major cause of PV. This gene makes a protein that helps the body produce blood cells. What causes the change in the JAK2 gene isn't known.