About the blood and bone marrow
The bone marrow is the soft, spongy tissue found in the center of large bones that stores immature cells called stem cells. Stem cells normally mature into white blood cells, red blood cells, and platelets during a process called hematopoiesis. In the body, white blood cells fight infections, red blood cells carry oxygen throughout the body, and platelets help the blood to clot.
About myelodysplastic syndromes
Myelodysplastic syndromes, also known as MDS, are a group of blood and bone marrow disorders. In MDS, stem cells do not mature normally, and the number of blasts (immature cells) and dysplastic (abnormally developed) cells increases. Also, the number of healthy mature cells decreases, meaning there are fewer normal red blood cells, white blood cells, and platelets. The numbers of blood cells are often called blood cell counts (see Diagnosis ).
Because of the decrease in healthy cells, people with MDS often have anemia (a low red blood cell count), and may have neutropenia (a low white blood cell count) and thrombocytopenia (a low number of platelets). There may also be changes (abnormalities) to the chromosomes (long strands of genes) in the bone marrow cells.
There are several subtypes  of MDS, and some subtypes of MDS may eventually turn into acute myeloid leukemia (AML) , a cancer of the blood in which immature cells called blasts increase and grow uncontrollably.
Find out more about basic terms used in this section .
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