Although Carly Todd, two, of Lennoxtown in Strathclyde, remains healthy, doctors at the Great Ormond Street Hospital in London cannot detect the gene they transplanted into her bone- marrow cells in March 1993.
Carly suffers a very rare deficiency of an enzyme - adenosine deaminase - that is vital for the immune system to function. Without treatment it leads to a build up of toxic substances in the blood.
Scientists took bone-marrow cells from Carly and infected them with a genetically engineered virus designed to transport a correct copy of the ADA gene into her cells. The bone marrow was then transplanted back into her body.
Dr Gareth Morgan, the consultant supervising the operation, said the initial results were promising. 'Analysis at two months showed the gene in the blood cells of the patient and at six months in the bone marrow but our latest analysis . . . does not show any evidence of the ADA gene,' he said.
Dr Morgan said Carly was healthy and living at home and there were no plans to repeat the gene therapy unless her condition deteriorated. Other gene therapy trials are planned by British doctors.