Genetic Mistake + Unknown Trigger = Leukaemia

Patricia Reaney / Reuters 4dec00

LONDON -- Childhood leukaemia is caused by a genetic abnormality that is present in one per cent of healthy babies and a second unknown trigger that occurs some time after birth, British scientists said on Monday.

The genetic mistake is crucial but not sufficient on its own to cause the malignant blood disease.

New research by scientists at the Institute of Cancer Research has shown that the genetic mistake is 100 times more common in children than leukaemia, proving that a so-called "double whammy" is necessary for the illness to develop.

"Something happens after birth. Unless you have the second hit you're OK. It is the second hit that is really crucial for determining who does and who doesn't get leukaemia," Professor Mel Greaves said in a telephone interview.

Greaves and his team, who will present their findings at the American Society of Haematology meeting in San Francisco, hope their work will eventually lead to a vaccination that could prevent leukaemia.

Children up to the age of 15 have a one in 2,000 risk of developing the disease.

The scientists screened the blood of 530 babies and found the non-inherited gene abnormality for leukaemia in six infants.

"Clearly the genetic mistake that starts leukaemia in the womb occurs more commonly that we had anticipated," he said, adding that only one in 100 with the abnormality will develop the disease.

Scientists are not sure what causes the mutation, or error in the developing foetus, but they think it is due to a natural accident during development.

"We basically don't know," was Greaves' simple answer.

The researchers are equally puzzled about the second trigger but suspect it could be the exposure to chemicals, radiation or infections. Scientific evidence seems to be pointing towards infection.

"What we think it is, is an abnormal immune response to perhaps a number of common infections, including bacterial infections," he explained.

"We think that if you happen to be one of these one per cent of children who have been born with this abnormal gene and if your bone marrow is stressed following infection you then may precipitate the second of a double whammy," Greaves added.

Dr David Grant, the scientific director of the Leukaemia Research Fund, said the study would improve the understanding of leukaemia.

"We need to identify the post-natal event which turns the possible into the probable and then turn that into an effective preventive strategy," he said in a statement.

Leukaemia occurs most often in children aged three to four years. In 80 per cent of cases, it is curable with a combination of chemotherapy and radiation.