It is one of the most dramatic improvements in success rates I know of

Dr Paul Veys, Great Ormond Street Hospital for Children

If there is a brother or sister who can provide matching bone marrow, this is most the most successful treatment.

For the rest, the only option is an transplant from an unrelated donor, and although many patients find drugs which suppress the immune system can help, there are still those who fail this way.

Remarkable improvement

Other options, such as umbilical stem cells, or transplants from a parent, are not sufficiently advanced to work in these patients.

In 1997, survival rates for this group were between 30% and 50%.

Consultant Dr Paul Veys, a consultant in bone marrow transplantation from Great Ormond Street, said: "Ten years ago, perhaps 20% of patients in this group survived.

"In 1997, the results were between 30% and 50%.

"In our latest group of patients - about a dozen cases - the success rate is practically 100%.

"It is one of the most dramatic improvements in success rates I know of."

Bristol Royal Hospital for Sick Children has also been using the technique, and joint results were published in the British Journal of Haematology.