Myelodysplastic syndrome (MDS) is a rare type of blood cancer whereby the bone marrow does not produce enough healthy blood cells, sometimes also referred to as myelodysplasia or bone marrow failure.

The bone marrow is the spongy material inside the bones where new blood cells are produced. The normal process of blood cell production starts with a stem cell, which is an immature cell that can develop into all types of blood cell. When the stem cell divides, it can either produce more stem cells or produce immature blast cells with the potential to further develop and mature.

The immature blast cells can mature and develop in the bone marrow to become the three types of blood cells: red blood cells, white blood cells, or platelets. All blood cells have an important function.

• Red blood cells (also called erythrocytes) – carry oxygen around the body to organs and tissues
• White blood cells (also called leukocytes) – protect against illness & disease by fighting infections
• Platelets (also called thrombocytes) – help blood clot to prevent bruising and bleeding.

In MDS, the bone marrow fails to produce healthy blood cells and instead makes abnormal cells that are unable to function normally. There are many different types of MDS classified based upon the type or types of blood cell affected and the extent of immature non-functioning blood cells present.

All types of blood cell may be affected which can cause a range of symptoms depending upon the cells affected. The severity of symptoms may vary depending on the type of MDS, from no symptoms to severe symptoms. For many patients, symptoms may be mild at first but may worsen over time.

In 2016 the World Health organisation changed the classification for MDS. The six main broad types of MDS are:

• MDS with single lineage dysplasia (MDS-SLD) – dysplasia in only one blood cell type.
• MDS with multilineage dysplasia (MDS-MLD) – dysplasia in 2 or 3 types of blood cell.
• MDS with excess blast cells (MDS- EB); MDS-EB-1 and MDS-EB-2. – number of immature abnormal cells called blasts.
• MDS with ring sideroblasts (MDS-RS) – young red blood cells with a distinctive ring of iron granules observed using a microscope.
• MDS, unclassifiable (MDS-U).
• MDS with isolated del(5q) or with 1 additional abnormality – a specific type where genetic testing reveals that part of chromosome 5 is missing.

MDS develops when something goes wrong with the normal process of healthy blood cell production in the bone marrow. All blood cells start off as stem cells which, in response to the need for more blood cells, develop and mature into healthy fully functioning blood cells which then migrate into the blood stream.

MDS occurs when stem cells die in the bone marrow, or do not divide or the blast cells do not mature and remain in the bone marrow. The result is that the immature cells may crowd out the bone marrow leaving less room for the production of new healthy blood cells. The result is fewer healthy functioning blood cells.

Failure to produce sufficient health blood cells may result in low blood cell counts often referred to as cytopenias. Cytopenias are a hallmark feature of MDS and are responsible for many of the symptoms that MDS patients experience such as repeated infections, anaemia, spontaneous bleeding, or easy bruising. In addition to reduced numbers of blood cells, any mature blood cells circulating in the blood may not function properly. Reduced blood count and non-functioning blood cells can have a significant effect upon the health of a person diagnosed with MDS.

The bone marrow’s failure to produce healthy blood cells may be a gradual process and therefore MDS may not be a life-threatening disease. There are many different types of MDS, some types can remain mild for years and others may be more serious.