Causes and Risk Factors
Doctors don't know why some cells become juvenile myelomonocytic leukemia (JMML) and others don't. They've found few risk factors associated with the disease.
Scientists have established a link between JMML and a rare genetic condition called neurofibromatosis 1. Children with neurofibromatosis are about 500 times more likely to develop JMML or another myeloid disease than are children who don't have the condition.
How Does JMML Develop?
JMML is considered a clonal disorder, meaning that it starts with one or more changes (mutations) to the DNA of a stem cell in the bone marrow. Stem cells form blood cells (white cells, red cells and platelets). The abnormal change(s) affects a white cell called a monocyte, transforming it into a JMML cell.
Normally, monocytes make up about 5 percent to 10 percent of cells in our blood. Monocytes, along with other white cells called neutrophils, are in charge of ingesting and killing microbes (germs) in the blood. When monocytes leave the blood and enter the tissues, they can attack invading organisms and help combat infection and assist other blood cells such as lymphocytes in carrying out their immune function.
JMML cells multiply uncontrollably and crowd out normal white cells, red cells and platelets. If not treated, JMML can lead to:
- low numbers of red cells that can no longer supply an adequate amount of oxygen, resulting in anemia
- the immune system's inability to guard against infection effectively because of a lack of neutrophils (a type of white cell), a condition called neutropenia
- low numbers of platelets, which can cause bleeding and easy bruising with no apparent cause, a condition called thrombocytopenia