A bone marrow disease which results in insufficient red blood cells in the blood (anemia). The prognosis is poor with death usually occurring within a couple of years. There are two types: type 1 refers to cases where the level of blasts is less than 10% and type 2 refers to cases where the level of blasts is 10-20%. When too many immature blood cells (blasts) are produced by the bone marrow, the condition may progress to acute myeloid leukemia - occurs in about a quarter of cases in type 1 and a third of cases in type 2. See also Anemia, Refractory, with Excess of Blasts