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Gene therapy. Suddenly, like a flag raised on the horizon, these words have arrived on the medical frontier, changing the world of medicine forever.

Scientists say this new form of treatment will be able either to cure or control a score of seemingly incurable diseases. The list includes several cancers, cystic fibrosis, AIDS, a rare inherited blood disease that acts like AIDS, hemophilia, and more. In 1 week in November 1993, the American Medical Association published 150 reports on the subject, trumpeting the quickening pace of these advances.

Genes are bundles of chemicals deep in your cells that manage the vast and complex chemical factories in muscles, nerves, skin, and bones. Humans have at least 100,000 genes, each controlling a different function. Sick or missing genes can mean cancer, deformity, or early death. Repair the sick genes or install the missing ones, and, in theory, you’ll have healthy cells and a healthy body. This is what gene therapists do.

On September 14, 1990, Ashanthi DeSilva, then 4, became one of the first to receive gene therapy. She suffered from a rare blood disease passed on to her by her parents, who weren’t sick. Lacking a particular gene, her blood cells could not make ADA, a chemical white blood cells need to fight infection. Her parents, Raj and Van DeSilva of Avon Lake, Ohio, watched their infant develop severe chest and ear infections within 2 months of her birth. She ran high fevers, suffered from diarrhea, and failed to gain weight.

Ashanthi was 2 before her illness was diagnosed. Fortunately, a pharmaceutical company had produced a cow’s blood derivative, PEG-ADA – a type of ADA that can be injected frequently enough to keep the immune system going. For Ashanthi, it was lifesaving. But, as she grew, she was kept from school for fear she would catch a germ too tough for her fragile immune system to handle.

Meanwhile, the human gene for making ADA had been isolated and copied, and scientists at the National Cancer Institute (NCI) and the Heart, Lung, and Blood Institute -both in Bethesda, Maryland -were developing an ADA deficiency treatment.

To get the ADA genes into Ashanthi’s white blood cells, her white cells were harvested, then grown in laboratory dishes. The lab-grown ADA gene was then spliced into a harmless virus. If the theory worked, the virus with the ADA gene would enter the white cells in the dishes. The white cells, now fortified with ADA from the virus, would be injected back into Ashanthi, ready to fight off infection.

The theory was applied in 1990. It worked. At first, Ashanthi had frequent treatments; now an annual treatment suffices. And she goes to school.

Dr. R. Michael Blaese, department chairman of NCI’s Metabolism Branch, led the team that prepared the new treatment. Since then, he said, he has given such therapy to more patients. Although his work looks promising, it will be a few years before the vaccine can be offered to everybody.

Dr. George D. Lundberg, chief editor of the AMA’s scientific journals, predicts, “Genetic diagnoses, screening, prevention, and treatment will expand enormously, with great potential for improvement – and for generating ethical conflict. The science of genetics is now soundly based and moving at such speed that we have new discoveries daily.”

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