THE announcement this summer that the "code of life" had been cracked was rightly hailed as one of the major scientific breakthroughs in the history of mankind.
But mapping the entire human genome - the sequence of DNA that is the blueprint for every individual - is not simply an intellectual exercise. Its applications within medicine will be almost limitless. Knowing our genetic make- up will allow doctors to tackle the root causes of illness. If a gene is faulty it can be repaired.
If it's missing it can be replaced. There is a long way to go before gene therapy becomes routinely available. But for sufferers of genetically determined illnesses everywhere it will mean, at last, the chance of a cure. Six-year-old Courteney Pearson and 47-year-old Liz Spour were both born withgenetic disorders. Their illnesses and stories are both very different yet gene therapy would provide more effective treatment - even a cure for both.
COURTENEYPearson was born with a rare inherited illness which was slowly poisoning her body. She was two weeks old when she was diagnosed with propionic acidaemia, a condition in which vital enzymes, produced mainly in the liver, are missing.
This leads to a build-up of toxins which poison the brain, causing brain damage or death by the age of seven. Courteney owes her life to an amazing piggy-back liver transplant when she was 22 months old. She became the first person in the world to have the pioneering surgery to beat an incurable metabolic disorder.
But although the intricate 10- hour operation cured the condition and saved her life, it condemned Courteney to a lifetime of immuno-suppressant drugs. Now, five years later, she still needs five drugs a day to ensure she does not reject her new liver. Gene therapy could release her from that lifelong medication.
It was this that convinced liver transplant surgeon NigelHeaton to remove only 70 per cent of Courteney's own liver and replace it with a healthy donor liver. He left nearly athird of her own defective liver behind in the hope that one day gene therapy could correct it.
This was much more difficult than a whole transplant, due to the problems of joining veins and arteries to two different livers. But it has been a total success. "Courteney is fantastically well now," says her mother Amanda, from Dover, Kent. "If she hadn't had the transplant she would be brain-damaged or dead by now.
"Yet she can look forward to her seventh birthday next month, and in five years time there is every chance that there will be an injection available which will provide the enzymes she needs to correct her own liver." Since Courteney's world- beating liver swap, Nigel Heaton has carried out six similar piggy-back transplants on children with different metabolic disorders at King's College Hospital in South London, the only unit in the UK using the technique.
"Leaving part of the patient'sown liver behind makes them suitable for genetherapy when it …