What Are Myelodysplastic Syndromes (MDS)?

Myelodysplastic syndromes (MDS) are a group of bone marrow diseases. They have a higher risk of becoming acute myelogenous leukemia (AML). These diseases all have different symptoms and treatments.

These diseases affect how the bone marrow creates healthy blood cells. About 10,000 people develop MDS in the United States each year.​

MDS is also called preleukemia, hematopoietic dysplasia, subacute myeloid leukemia, oligoblastic leukemia, or smoldering leukemia.

This article explains how someone gets MDS, what puts someone at a higher risk, and the symptoms of these diseases.

Red blood cells
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How Does MDS Develop?

MDS begins with DNA damage in a single blood-forming stem cell. The bone marrow starts to make too many blood cells and gets packed with immature cells. These are also called "blast" cells.

There is also an increase in cell death. There may be more cells in the marrow but they do not live long enough to get out into the blood. This is why people with MDS often have complications related to a lack of blood cells. These include a low red blood cell count, a low platelet count, and a low white blood cell count.

Platelets help the blood clot to stop bleeding. Red blood cells help circulate oxygen in the body. White blood cells help fight infections and disease.

Risk Factors

The cause of MDS is not known. About 90% of the time, there is no obvious cause of the disease. Some possible risk factors that impact whether someone will get MDS include:

  • Age: The median age of diagnosis is 70, although MDS has been seen even in young children.
  • Ionizing radiation: This includes radiation treatments for cancer or exposure to radiation from atomic bombs and nuclear accidents.
  • Chemical exposures: Exposure to some organic chemicals, heavy metals, fertilizers, pesticides, and herbicides raises the risk of the disease.
  • Tobacco smoke
  • Diesel exhaust

Is It a Preleukemia?

The number of blast cells in the marrow shows how severe the disease is. More immature cells mean more severe disease. Once your marrow shows that it's made up of more than 20% blast cells, it is considered to be AML.

About 30% of cases of MDS become AML. Even if this does not happen, other blood problems related to MDS are still life-threatening.

MDS Subtypes

MDS includes several different bone marrow disorders. Each condition has subtypes that determine the behavior and outcome. There are a few classification systems that try to cover these different types.

FAB classification

The first system is the French-American-British (FAB) classification. It breaks MDS down into 5 subtypes. These are based on how the bone marrow looks and the results of the patient’s complete blood count (CBC):

  • Refractory anemia (RA)
  • Refractory anemia with ringed sideroblasts (RARS)
  • Refractory anemia with excess blasts (RAEB)
  • Refractory anemia with excess blasts in transformation (RAEB-T)
  • Chronic monomyelocytic leukemia (CMML)

The FAB criteria were created in 1982. Since then, scientists have learned more about the genetic abnormalities that lead to MDS. They have also studied how these mutations impact the course of the disease.

WHO classification

In 2001, the World Health Organization (WHO) published some changes to the FAB system. They added some conditions that include:

  • 5q-syndrome
  • MDS unclassifiable (MDS-U)
  • Refractory cytopenia with multilineage dysplasia (RCMD)

WHO subdivided RAEB and CMML based on the percentage of blasts in the bone marrow. They also explained that greater than 20% of blasts in the marrow was considered AML.


The third system is the International Prognostic Scoring System (IPSS). It uses three criteria for determining how MDS will progress:

  • Number of cells in the patient’s circulating blood
  • Number of immature blast cells in the bone marrow
  • Cytogenetics (the type of genetic abnormalities related to the MDS)

IPSS divides patients into four categories. These show the “risk” of the MDS: low, intermediate-1, intermediate-2, and high. The IPSS provides a better way to predict outcomes and plan treatment.


There are a few systems to help classify MDS disorders. Some types are divided into subtypes based on how many blast cells are in the bone marrow. When MDS causes more than 20% of cells in the bone marrow to be blast cells, it means it has developed into AML.

Primary vs. Secondary MDS

In most patients, MDS seems to develop suddenly for no known reason. This is called primary or de novo MDS. Scientists are not sure what causes primary MDS.

Secondary MDS means the disease follows previous treatment with chemotherapy or radiation therapy.


MDS is diagnosed using the same techniques used to diagnose leukemia.

The first test is a complete blood count (CBC). This test looks at the number of healthy red blood cells, white blood cells, and platelets in the blood. This gives an idea of what is going on in the marrow.

A person with MDS will usually have low numbers of red blood cells. They could have low platelets and white blood cells as well.

If there is no other clear cause for anemia, the doctor will perform a bone marrow aspirate and biopsy. This involves inserting a needle into the bone to remove a test sample.

A patient with MDS will have abnormal bone marrow and an increased number of blast cells. They will also show mutations or changes to the chromosomes.

Signs and Symptoms

Patients with MDS may experience symptoms of low red blood cells such as:

  • Shortness of breath with little effort
  • Pale skin
  • Feeling tired
  • Chest pain
  • Dizziness

A few patients will also have signs of low platelet and low white blood cell counts. This may include bleeding problems and difficulty fighting off infections.

There are many other, less serious conditions that can cause these signs and symptoms. It is best to discuss any health concerns with your doctor.


MDS is not one disease. It is a group of conditions that cause changes to how the bone marrow functions.

Scientists continue to learn more about genetics and how these diseases develop. They are also learning more about risks and the outcomes of these diseases. Researchers can use this information to create new and more effective therapies for MDS.

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Additional Reading

By Karen Raymaakers
Karen Raymaakers RN, CON(C) is a certified oncology nurse that has worked with leukemia and lymphoma patients for over a decade.