Juvenile myelomonocytic leukaemia (JMML)
Juvenile myelomonocytic leukaemia (JMML) is a very rare type of slowly developing (chronic) blood disorder that occurs in young children. It is 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 do not classify it as a leukaemia. It is now included in a group of diseases called myeloproliferative and myelodysplastic disorders. A myeloproliferative disorder is a condition where there are too many blood cells made. And 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.
The abnormal white blood cells are made in the bone marrow, enter the bloodstream and circulate around the body. They do not work normally and so children with JMML do not have the same protection against infection as they should. The under developed blood cells are called blasts. In JMML it is white blood cells called monocytes that are abnormal. Monocytes are part of the immune system and help the body to fight infection.
JMML is most common in children under 4. As with many types of cancers, we do not 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.
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
- Getting lots of infections
- An enlarged liver and spleen
- Swollen lymph nodes
- Skin rashes
- Small yellowish skin tumours
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.
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