Acute lymphoblastic leukaemia is caused by a DNA mutation in the stem cells causing too many white blood cells to be produced.

The white blood cells are also released from the bone marrow before they are mature and able to fight infection like fully developed 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 leukaemia.

It is not known exactly what causes this DNA mutation to occur, but there are a few factors which may increase the risk of developing acute lymphoblastic leukaemia.

Risk factors

Genetic disorders

A small number of childhood acute lymphoblastic leukaemia cases are thought to be caused by related genetic disorders. For example, rates of leukaemia tend to be higher in children with Down’s syndrome.

Radiation exposure

Exposure to very high levels of radiation, either before birth or afterwards, is a known risk factor. However, it would require a significant level of radiation, such as the amount released during the nuclear reactor accident at Chernobyl.

Due to the potential risk of radiation to unborn babies, medical techniques and equipment that use radiation, such as X-rays, are rarely used on pregnant women.

Most cases of childhood leukaemia occur in children with no history of genetic disorders or exposure to radiation.

Possible environmental factors

Experts have also carried out extensive research to determine whether the following environmental factors could be a trigger for leukaemia:

• living near a nuclear power station
• living near a power line
• living near a building or facility that releases electro-magnetic radiation, such as a mobile phone mast

At the moment there is no evidence to confirm that any of these environmental factors increases the risk of developing leukaemia.

Benzene

Exposure to the chemical benzene is a known risk factor for adult acute leukaemia. Benzene is found in petrol and is also used in the rubber industry. However, there are strict controls to protect people from prolonged exposure.

Benzene is also found in cigarettes, which could explain why smokers are three times more likely to develop acute leukaemia than non-smokers. People who have had chemotherapy and radiotherapy to treat earlier, unrelated cancers also have an increased risk of developing acute leukaemia.

Other risk factors

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

• are obese
• have a weakened immune system – due to HIV or AIDS or taking immunosuppressants after an organ transplant