Myelodysplastic syndromes (MDS) are a rare group of blood disorders that occur as a result of disordered development of blood cells within the bone marrow. The three main types of blood elements (i.e., red blood cells, white blood cells and platelets) are affected. Red blood cells deliver oxygen to the body and remove carbon dioxide, white blood cells help fight infections, and platelets assist in clotting to stop blood loss. In MDS dysfunctional blood cells fail to develop normally and enter the bloodstream. As a result, individuals with MDS have abnormally low blood cell levels (low blood counts). General symptoms associated with MDS include fatigue, dizziness, weakness, bruising and bleeding, frequent infections, and headaches. In some cases, MDS may progress to life-threatening failure of the bone marrow or develop into an acute leukemia. The exact cause of MDS is unknown. There are no clear risk factors but genetics and the environment may play a part. Myelodysplastic syndromes were first noted in the medical literature in 1930s where they were described as pre-leukemic conditions. Myelodysplastic syndromes were not regarded as separate, distinct disorders until 1976. In the past, these disorders have also been known by a variety of names including refractory anemia, oligoblastic anemia, myelodysplastic anemia, pre-leukemia, and smoldering leukemia.