Some of the most serious medical problems are caused by genes that fail to produce a necessary protein or produce a flawed version. Scientists have realized for a quarter century that it should be possible to cure such conditions by replacing the faulty genes with ones that work properly. They have learned how to find the genes in question in healthy cells and cut them from longer stretches of DNA. They have learned how to introduce the "good" genes into viruses that will serve as vectors; "the whole purpose of a virus is to insert its DNA into a cell."
Up until now, at least, researchers have not been able to use gene therapy to permanently cure a disease, however. The whole thing turns out to be far more complicated than first thought. And the whole effort suffered a severe setback when a teenage patient died during a gene therapy trialapparently from the virus, not the introduced gene. In fact, Theodore Friedmann, a pioneer who coauthored a seminal paper in 1972, won't use the phrase "gene therapy," preferring "gene transfer" in its place to describe the state of current research.
Recently, teams of researchers in France and the United States have reported small successes. In the first, the group corrected an immune deficiency in two infants. In the other, the scientists injected viruses carrying the necessary gene into three people with hemophilia. A year later, two of them were producing a blood clotting factor that hemophiliacs lack.
In principle, gene therapy has the potential to do more than cure diseases involving faulty genes. Consider patients with coronary artery disease, a condition in which vessels are partly blocked so that tissue downstream from the blockages doesn't get enough blood and therefore enough oxygen. In such cases, the body will naturally generate more blood vessels, to provide what is known as collateral circulation. But often the body cannot keep up, and oxygen-starved cells generate the pain known as angina. By adding genes that produce an angiogenic growth factor to the body, the collateral circulation can be speeded up and increased.
From that kind of enhancement, however, it is an easy jump to introducing genes that will improve a perfectly healthy body. Suddenly we are close to eugenics, a discredited science (the Nazis were big believers) of improving the breedour own.
Gene therapy has enormous potential, and every day scientists move closer to having it succeed with patients. That will be great day for a lot of people.