Myelodysplastic syndrome (MDS), or myelodysplasia, is a blood disorder that causes a drop in your number of healthy blood cells. MDS covers a spectrum of disorders from indolent (slow developing) to aggressive (that rapidly develop or change into leukaemia).

Normally, blood cells are made in the bone marrow, these include:

  • red blood cells to carry oxygen around your body
  • white blood cells to help fight infection
  • platelets to help your blood to clot

In MDS, your bone marrow doesn't make enough healthy red blood cells, white blood cells and/or platelets. Instead, it makes abnormal numbers of cells and/or cells that don’t work properly.

As the condition develops, your bone marrow becomes full of the abnormal blood cells, which may spill out into your bloodstream.

The most common types of myelodysplasia are:

  • refractory anaemia – just the red blood cells are affected
  • refractory cytopenia – the red blood cells, white blood cells and platelets are affected
  • refractory anaemia with excess blasts (RAEB) – the red blood cells, white blood cells and platelets are affected, and there's a higher risk of developing acute leukaemia

"Refractory" means the condition doesn't respond to treatment that doctors would normally use for low blood cell counts.

There are also other more rare types of MDS including

  • chronic myelomonocytic leukaemia
  • Secondary MDS

For most people, symptoms are mild at first and slowly get worse. Sometimes you may even have no symptoms at all, but have had a blood test that shows there is a problem. You may initially experience:

  • weakness, tiredness and occasional breathlessness –because of the low number of red blood cells
  • frequent infections –because of the low number of white blood cells
  • bruising and easy bleeding (such as nosebleeds) – because of the low number of platelets

Symptoms will depend on the type of MDS you have – for example, some people just have a problem with their red blood cells and have symptoms of anaemia, while others may lack all types of healthy blood cell.

MDS can affect people of any age, but is most common in people over the age of 65. Only one in five people with MDS are younger than 50.

In most cases, the cause is unknown – this is called primary MDS.

In rare cases, MDS is caused by radiotherapy or chemotherapy treatment for cancer. This is known as secondary MDS, or treatment-related MDS.

In very rare circumstances a family tendency to the disease can be identified because of an abnormal gene.

Yes. We know this because all the MDS blood cells carry some genetic mistakes that have caused them to develop abnormally. However, many patients with MDS do not require treatment for many years. Some people with MDS go on to develop acute myeloid leukaemia (AML), which is a more aggressive cancer of the white blood cells. This is known as "transformation".

The risk of transformation can be assessed using a scoring system called the International prognostic scoring system – Revised (IPSSR). You can see the information used to calculate this here

For the lowest risk patients the time to 25% of the patients getting leukaemia is more than 10 years. For the highest risk patients it is 9 months.

Support for patients with Myelodysplastic Syndromes and carers.