Bone marrow is a soft spongy material that is located inside of the bones. Bone marrow is necessary for the transition that stem cells make to become one of the types of blood cells (red blood cells, platelets or white blood cells). Bone marrow disease occurs when there is some kind of abnormality or interference with the production of blood cells. Leukemia, aplastic anemia and myelodysplastic syndromes (MDS) are three types of bone marrow disorders that affect the production of blood cells and the bone marrow. Symptoms of each type of bone marrow disease will vary according to its severity, but tend to be similar in nature.