The synonymous terms myelodysplasia and preleukemia refer to acquired abnormalities of the bone marrow that precede the onset of acute leukemia. These conditions are characterized by chronic anemia, often in combination with reduced white blood cell and platelet counts. Accordingly, patients with myelodysplasia experience symptoms of fatigue, recurrent infections, and easy bruising or bleeding. Paradoxically, despite the reduced numbers of mature blood cells in the peripheral blood, the bone marrow in myelodysplasia shows increased proliferation of developing blood cells. The development of these blood cells is abnormal, however, and their fate is to be destroyed before they can leave the marrow and enter the blood. Myelodysplasia is rarely diagnosed in patients younger than fifty years, and the peak incidence of this disease is seen in the age range eighty to eighty-four years. No cure for myelodysplasia is known, but the symptoms of this condition can be alleviated by transfusions of red cells and platelets and in some cases by injections of the hormone erythropoietin, which stimulates red cell production. These therapies do not alter the natural progression of myelodysplasia to acute leukemia, which may occur over the course of months or years, and which is heralded by the accumulation of cells called blasts in the marrow. These cells are the hallmark of acute leukemia.