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Gene therapy to cure boy's disease triggered leukaemia, doctors say
Last updated at 09:22am on 19.12.07
Danger: Gene therapy is thought to have potentially devastating side-effects
A boy treated with pioneering gene therapy has developed leukaemia as a result, say doctors.
The three-year-old was successfully treated at Great Ormond Street Children's Hospital two years ago for the condition X-SCID.
Commonly known as the "boy in the bubble syndrome", the condition is fatal as victims have no immune system and have to be kept in sterile surroundings.
But the gene therapy which gave the child a near-normal life led to leukaemia - a recognised side effect - which was diagnosed last month.
The boy was one of ten children with X-SCID treated so far at the hospital and the first to develop the chronic bone marrow disease.
A trial in France of similar therapy was halted in 2002 after four of the 11 children developed leukaemia.
Professor Bobby Gaspar, consultant immunologist on the gene therapy programme, said that all the children treated had benefited and had been able to lead "relatively normal lives".
He said: "All families were counselled as to the risks, and so far, this development has been the only negative one."
It is thought the gene therapy which restored the boy's immune system also switched on a gene causing leukaemia.
Safer genetic treatment that does not pose a leukaemia risk is being prepared for clinical trials next year.
One in 100,000 births in the UK is affected by severe combined immunodeficiency disorder (SCID), with the particular form of the disease X-linked SCID affecting only boys.
Sufferers are not expected to live beyond two years without treatment and are put inside a plastic tent in conditions of absolute isolation.
It can be treated with a bone marrow transplant to provide the missing immune cells which has a high success rate when there is a matched brother or sister donor, and fairly successful when the donor is a parent.
But only one-third of SCID children get a good donor match.
Gene therapy aims to help the child build a new immune system from within rather than borrowing one from a donor.
Bone marrow is taken from the patient under a general anaesthetic and treated with a virus which carries the correct version of a synthetic gene.
The genetically modified bone marrow is then infused into the child where it generates immune cells which pass into the blood.
But there had been warnings there was a risk of cancer, including long-term studies showing the effect in mice.
The childhood survival rate for leukaemia is around 80 per cent and it is thought the boy's original illness will not affect his chances of beating the disease.
He is still in remission from X-SCID.
