FIVE years after the first human being received gene therapy to correct an inherited disease, the results are in. The Washington Post (October 21, 1995) reports that two seriously ill children who were given immune-system genes that they lacked from birth, are "healthy and thriving" now. Gene therapy is a technique in which doctors give patients healthy genes to replace the defective ones inherited from their parents or to enhance the action of the genes they already have.

Researchers led by R Michael Blaese of the us-based National Centre for Human Genome Research (NCHGR) selected two young girls to debut the technique. They were born with an extremely rare genetic disorder called adenosine deaminase (ADA) deficiency. The disease occurs when a child inherits mutated versions of a gene responsible for making a crucial detoxifying enzyme. Without the enzyme, toxins build up in the blood, killing immune system cells and leaving patients defenseless against infections.

In the experiment, Blaese and his colleagues iried to add normal versions of the genes to the patients' cells. Beginning in 1991, four-year-old Ashanthi De Silva was administered about one billion of her own white blood cells, after they had been removed from her body and genetically altered. Soon after, the investigators treated another eight-year-old patient in the same way.

In a recently published paper, the researchers report that half of Ashanthi's cells carry the added ADA gene, and her cells are making 25 per cent of the normal amQunt of the enzyme. It is held that people who make just 10 per cent of norM.&I ADA levels show no symptoms of immune dysfunction. "I couldn't have wished for a nicer outcome", says Blaese, satisfied with the result of his experiment.

The result of the experiment significantly shows the potential of gene therapy. "I think people will no longer be able to say that gene therapy has never benefitted a patient", remarks F S Collins, director of the Nc#iGR. The success of the experiment is a milestone indeed, the first in a field that has so far failed to live up to expectations.