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Juvenile myelomonocytic leukaemia (JMML)

Get information on what JMML is, the symptoms and what treatment is available.

What it is

Juvenile myelomonocytic leukaemia (JMML) is a very rare type of slowly developing (chronic) blood disorder that occurs in young children. It's also sometimes called juvenile chronic myelogenous leukaemia (JCML).

Leukaemia means a cancer of the blood forming system. The blood forming system is the bone marrow – the soft inner part of your bones. Although JMML has leukaemia as part of its name, the World Health Organisation (WHO) does not classify it as a leukaemia. It's now included in a group of diseases called myeloproliferative and myelodysplastic disorders.

Myeloproliferative and myelodysplastic disorders

A myeloproliferative disorder is a condition where there are too many blood cells made. A myelodysplastic disorder is where the blood cells made are abnormal and not fully mature. In reality, these two disorders often overlap, which is why the WHO has put them together in the same category.

Problems with infections

The abnormal white blood cells are made in the bone marrow, enter the bloodstream and circulate around the body. They don't work normally, so children with JMML don't have the same protection against infection as they should. The under developed blood cells are called blasts. In JMML it's white blood cells called monocytes that are abnormal. Monocytes are part of the immune system and help the body to fight infection. 

Who gets JMML

JMML is most common in children under 4. We don't yet know the cause of JMML. Children with a genetic disorder called neurofibromatosis 1 (NF1) are more at risk of developing JMML. But this only accounts for about 1 in 10 cases.

Symptoms of JMML

In JMML, as the abnormal blood cells multiply in the bone marrow, fewer normal blood cells are made. If there are not enough normal blood cells, the body cannot work normally.

This can cause quite severe symptoms in children with JMML, including:

  • being tired and lethargic
  • bruising easily
  • nosebleeds and bleeding gums
  • fever
  • getting lots of infections
  • an enlarged liver and spleen
  • swollen lymph nodes
  • skin rashes
  • small yellowish skin tumours

Treatment for JMML

The treatment for JMML is usually a stem cell transplant. This is where doctors replace the damaged stem cells with healthy ones taken from a donor, often a brother or sister. At the moment this is the only type of treatment that can possibly cure JMML.

Unfortunately, this type of treatment is only suitable for some children. Doctors and scientists are trying to improve treatment for this disease, but currently it is still difficult to cure.


Coping with a diagnosis of a rare blood disorder can be especially difficult, both practically and emotionally. Being well informed about your child's condition and their treatment can make it easier to make decisions and cope with what happens.

Leukaemia CARE

Leukaemia CARE provides support to anyone affected by blood cancer. They have information on their website about myeloproliferative disorders.

Cancer Research UK nurses

For support and information, you can call the Cancer Research UK information nurses on freephone 0808 800 4040, from 9am to 5pm, Monday to Friday. They can give advice about who can help you and what kind of support is available.
Last reviewed: 
20 Jul 2017
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    D Choudhary and others

    Indian Journal of Hematology and Blood Transfusion, 2014

    Volume 30, Supplement 1

  • Subclonal mutations in SETBP1 confer a poor prognosis in juvenile myelomonocytic leukemia

    E Stieglitz and others

    Blood, 2015

    Volume 125, Issue 3

  • Principles and practice of oncology (10th edition)

    VT DeVita, TS Lawrence and SA Rosenberg

    Lippincott, Williams & Wilkins, 2015

  • The 2008 revision of the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia: rationale and important changes

    JW Vardiman and others

    Blood, 2009

    Volume 114, Issue 5


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