Chronic myeloid leukaemia - Causes of chronic myeloid leukaemia

Chronic myeloid leukaemia is caused by a DNA mutation in the stem cells which produce white blood cells.

The change in the DNA causes the stem cells to produce more white blood cells than are needed.

They are also released from the bone marrow before they are mature and able to fight infection like healthy 'adult' white blood cells.

As the number of immature cells increases, the number of healthy red blood cells and platelets fall, and it's this fall which causes many of the symptoms of chronic leukaemia.

Philadelphia chromosome

Although the cause of chronic myeloid leukaemia is genetic, it is not inherited as it is an acquired genetic abnormality.

Most people with the condition have an abnormal chromosome, where a section of DNA from one chromosome has been swapped with a section from another.

This is called the Philadelphia chromosome and it makes the cell produce a protein that encourages the leukaemic cells to resist normal cell death and grow and multiply far more quickly than usual.

Possible triggers for chronic leukaemia

What triggers the development of chronic leukaemia and causes the initial mutation in stem cells is unknown. The one proven risk factor is exposure to radiation.

However, radiation is only a significant risk if the levels are extremely high, such as those recorded after an atomic bomb explodes, or those released after a nuclear reactor accident, such as the one at Chernobyl.

Benzene

There is limited evidence that prolonged exposure to the chemical benzene leads to an increased risk of chronic myeloid leukaemia. Benzene is found in petrol and is also used in the rubber industry, but in the UK there are strict controls to protect people from prolonged exposure.

Benzene is also found in cigarettes. However, it is thought that smoking is more of a risk factor in acute leukaemia than it is in chronic leukaemia.

Occupational risks

A number of occupations have been linked to an increased risk of chronic leukaemia, possibly due to exposure to certain substances such as pesticides or chemicals.

These occupations include:

• all types of agricultural workers
• people who are involved with rubber or plastic manufacture
• tailors and dressmakers
• cleaners
• builder’s labourer

Other risk factors

There is some evidence to show an increased risk of chronic leukaemia in people who:

• are obese
• have a weakened immune system – due to HIV or AIDS or taking immunosuppressants after an organ transplant
• have inflammatory bowel disease – such as ulcerative colitis or Crohn's disease