Although there is no single cause of polycythemia vera, it is known that there are a number of factors that contribute to the abnormal production of red blood cells, which would be the origin of this blood disorder:
-Increased sensitivity to erythropoietin. The red blood cell precursors are more sensitive to the stimulus that erythropoietin generates to form erythrocytes or red blood cells.
-Alterations in hematopoietic factor receptors: this means that there is an abnormal response to stimuli of other blood substances (hematopoietic factors) in the receptors of a protein called thrombopoietin, which will lead to an uncontrolled and pathological formation of red blood cells.
-Chromosomal alterations. In a variable percentage of patients with polycythemia vera anomalies are detected in chromosomes 8, 9, 17 and 20 that could explain this disease. In the case of chromosome 9, there is a point mutation of the JAK2 gene, which has recently been cited as the most determining factor for the development of this disease. It is estimated that more than 90% of them express this mutation as a cause of polycythemia vera.
-Endogenous formation of red blood cells. It could be an individual predisposition without an alteration as well known as the previous ones, idiopathically. In these cases, patients present an exaggerated production of erythrocytes without the need for stimuli such as erythropoietin, without evidence of alterations in their receptors or other factors.
Types of polycythemia vera
The polycythemia is characterized by an increase in the blood of the number of red blood cells, and there are two types of polycythemia:
- Primary polycythemia or polycythemia vera: is an alteration of the hematopoietic stem cell (precursor cell that gives rise to different blood cells), characterized by an uncontrolled proliferation of blood cells (white blood cells, red blood cells and platelets). Although the predominance of red blood cells is the characteristic feature of the disease, the increase in white blood cells and platelets is also frequent.
The causes of the malignant transformation that occurs in polycythemia vera are unknown. The description in 2005 of a mutation acquired from the JAK2 gene in more than 90% of those affected by polycythemia vera has allowed to know better the disease. Its incidence is 0.7-2.6 cases per 100,000 people per year, and it is slightly more frequent in males, especially affecting people between the ages of 50 and 70 years. It is rare before age 40 (4% of cases).
- Secondary polycythemia or secondary erythrocytosis: refers to those situations in which only red blood cells are increased in number. In turn, secondary polycythemia can be subdivided into:
- Appropriate polycythemia: the increase in the number of red blood cells occurs in response to hypoxia (low amount of oxygen in the blood). Such increases can be observed, for example, in people who live at high altitudes, in people who smoke a lot, and in patients with cardiopulmonary disease.
- Inappropriate polycythemia: the formation of red blood cells (erythropoiesis) is being stimulated by the abnormal production of erythropoietin (EPO). This occurs, for example, in people suffering from hereditary diseases or tumors.