Molecular biology of polycythemias

Polycythemia is literally translated as "many cells in the blood". Only ery throcytosis (an alternative term for these disorders) produces polycythemia since leukocytes and platelets are present in blood in far smaller proport ions. Polycythemia may be due to increased proliferation or decreased apopt osis of erythroid progenitors, or to delayed erythroid differentiation with an increased number of progenitor cell divisions. Prolonged red cell survi val, another theoretical cause of polycythemia, has not yet been described and with intact regulatory mechanisms is unlikely to occur. Primary polycyt hemias result from abnormalities expressed in hematopoietic progenitors. In contrast, circulating factors cause secondary polycythemia (1). There are acquired and congenital causes of both primary and secondary polycythemia ( 1).