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Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

What Is It?

Myelodysplastic syndromes (MDS) are diseases in which the bone marrow does not make enough healthy blood cells. Bone marrow is the soft, inner part of bones. Normally, it produces three kinds of blood cells:

  • red blood cells, which carry oxygen

  • white blood cells, which fight infection and disease

  • platelets, which help prevent bleeding by causing blood to clot.

Healthy bone marrow makes immature cells called stem cells that develop into red and white blood cells and platelets.

In MDS, the bone marrow cannot produce the right kind of blood cells. These abnormal cells either die in the bone marrow or soon after they enter the bloodstream. As a result, people with MDS don't have enough healthy blood cells and are said to have low blood cell counts. This can lead to:

  • anemia, caused by not enough red blood cells

  • infections, caused by not enough white blood cells

  • bleeding and bruising, caused by not enough platelets.

Many experts consider MDS an early stage of cancer. In about 30% of patients, the disease will develop into acute myeloid leukemia (AML), a cancer of bone marrow cells.

In most cases, the cause of MDS is not known. The biggest risk factor for MDS is having had treatment for cancer with chemotherapy and radiation therapy. Exposure to certain chemicals has also been linked to MDS. Some people may be born with a tendency to develop MDS.

Most patients with MDS are over age 60. The disorder is slightly more common in men than women. It is also slightly more common in whites than in other racial groups.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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