Myelodysplastic syndromes (MDS) types

Doctors split MDS into different types using a set of instructions called a classification system. Until recently, the main classification system was published by the World Health Organisation (WHO). The most recent edition of this was published in 2022. But in the same year another group of experts published a different classification, called the International Consensus Classification.

At the moment, not all doctors agree on which classification system to use. Until doctors have reached an agreement, the British Society for Haematology says doctors should use the 2016 version of the WHO classification. If this changes, we will update this page.

To decide what type of MDS you have, your doctor will look at:

• the levels of different blood cells in your blood
• what cells from your bone marrow look like under a microscope
• any changes in a part of your blood cells called chromosomes, and the genes inside them.

There are six main types of MDS.

If you have this type of MDS, it means just one type of blood cell in your bone marrow is abnormal. You will also have low levels of one or two types of blood cell in your blood.

If you have this type of MDS, it means two or three types of blood cell in your bone marrow are abnormal. You will also have low levels of one, two or three types of blood cell in your blood.

Red blood cells are partly made from iron. In people with this type of MDS, their red blood cells don’t process iron properly. This shows up under a microscope as a ring of iron particles – called ring sideroblasts – inside the cell. Most people with this type of MDS have a mutation in a gene called SF3B1.

There are two sub-types of MDS with ring sideroblasts:

• MDS-RS with single lineage dysplasia – this means the MDS affects just one type of blood cell.
• MDS-RS with multilineage dysplasia – this means the MDS affects two or more types of blood cell.

Blasts are immature blood cells that haven’t turned into fully developed healthy cells. In MDS with excess blasts, you have too many blasts in your bone marrow or blood. You also have low levels of one, two or three types of blood cell in your blood. This type of MDS is split into two types depending on the number of blasts:

• MDS-EB-1
• MDS-EB-2

Some types of MDS involve changes in the chromosomes of blood cells. Chromosomes are the packages of genetic material inside all cells. We each have 23 pairs of chromosomes in almost every cell of the body. One type of MDS has a specific change called isolated del (5q), which means that part of chromosome 5 is lost. If you have this type of MDS, you will have low levels of one or two types of blood cell in your blood.

This means any type of MDS that doesn’t fit into the groups above. If you have a type of unclassifiable MDS, your medical team can explain more about it.