Myelodysplastic syndromes (MDS) are a group of disorders where the bone marrow produces poorly formed or malfunctioning blood cells. This occurs when the blood cells fail to mature properly and die either in the bone marrow or shortly after entering the bloodstream. As a result, there are more immature, defective cells than healthy ones, causing symptoms like fatigue (due to anemia), infections (from a lack of white blood cells), and bleeding (due to low platelet count). The majority of MDS cases have no known cause.