Myelodysplastic syndrome (MDS) is a group of diseases that affects normal blood cell production in the bone marrow. In MDS, the bone marrow produces abnormal, immature blood cells called blast cells. These cells fail to mature properly are unable to work properly. They often die before they leave the marrow, or shortly after reaching the bloodstream. Without enough normal cells being produced by the marrow (red cells, white cells and platelets) people with MDS can become fatigued, more susceptible to infections, and to bleeding and bruising more easily.
There are several different types of MDS and the disease can vary in its severity and the degree to which normal blood cell production is affected. About 30% of people with MDS will progress to a form of cancer called acute myeloid leukaemia (AML). It is sometimes referred to as a pre-leukaemic disorder.