Causes

The bone marrow is where blood cells are made. There are three different types of blood cells that carry out different functions in the body:

• White blood cells, which help the body fight infection and disease
• Red blood cells, which move oxygen from the lungs throughout the body
• Platelets, which help control bleeding by forming clots

Cells in the bone marrow that mature into various types of blood cells are called blasts. Granulocytes are the type of blasts that mature into white blood cells. In CML granulocytes do not mature normally. Too many of these cells develop and they do not function correctly.

In about 95% of patients with CML, a defect in a chromosome (the genetic material) in the leukemia cells occurs. This defect is called the Philadelphia chromosome, named for the city where it was discovered. This abnormal chromosome forms when two chromosomes in the cell swap their genetic material. It is not clear what causes this to happen. Because of this event a protein that normally helps to regulate the production of new white blood cells in the bone marrow - the Abl protein – becomes stuck in the "on" position, telling the body to keep making more abnormal blood cells.

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