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USING GENETIC engineering techniques that already are being tested in mice, scientists may one day be able to modify the DNA in our eggs and sperm, or in the cells of young embryos, introducing healthier, “better” genes.
Unlike current gene therapy techniques, which affect only the person whose tissue is being modified, the altered egg, sperm or embryonic DNA would be passed to one’s offspring and show up in generations to come.
While originally conceived as a technique for wiping out certain genetic disorders such as cystic fibrosis, there’s nothing to prevent the methods from being used to enhance such traits as eye color, intelligence and even creativity, scientists say. Parents could conceivably make a list of the traits they would like their children to have, check in for a few gene alternations and voila — a designer child is conceived.
Images of a totalitarian society filled with smarter, more beautiful people underestimate the potential dangers of the new techniques, some say. Tampering with DNA can have unexpected effects, since how one gene behaves often depends on its neighbors. By manipulating the gene for, say, cystic fibrosis, you may unknowingly be modifying the function of a gene that predisposes you to heart disease. Moreover, the effect may not show up for generations.
But if the techniques can be made safe, the potential benefits are just as enormous, they add. Current methods demand correcting a defect over and over in each generation. “Think of how much more efficient it would be to correct a genetic defect just once in an embryo, have that embryo grow into a healthy person and transmit the healthy gene to offspring,” says Dr. Theodore Friedmann, director of the human gene therapy program at the University of California, San Diego.
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‘Are we wise enough to tinker not just with one life, but with the lives of all that person’s descendents?’
— THOMAS MURRAY
Case Western Reserve University
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At a two-day seminar sponsored by the American Association for the Advancement of Science in Washington, D.C., this week, scientists and ethicists grappled with the issues posed by the new science.
UNDERSTANDING GENE THERAPY
Gene therapy is not a new idea: Ever since scientists realized that certain disorders were associated with specific genetic flaws, they have sought ways to correct the underlying problem — that is, to fix the bad genes by introducing healthy, new ones.
So far, gene therapy studies have been at the tissue level, aimed at modifying DNA in cells, such as skin and liver cells, which are not passed to future generations, Friedmann explains. While so-called somatic gene therapy has yet to cure even a single person, scientists at the conference agree that it won’t be long before the technique’s potential is realized.
And as somatic gene therapy becomes more sophisticated, more permanent gene fixes, which had been pushed aside in the early 1980s, are being put back on the table, says Thomas Murray, an ethicist at Case Western Reserve University in Cleveland.
Known as germ-line gene therapy, the new techniques are a form of genetic manipulation aimed specifically at reproductive or embryonic cells, with the modified DNA passed to one’s descendents in the germ line.
Before germ-line therapy is even attempted, a host of new scientific hurdles have to be overcome. First, scientists will want to ensure that the therapy works in “lots of animal tests,” Murray says. And right now, for every 70 successes scientists are having in mice, there are some 30 failures, Friedmann says. Then, they’ll want to ensure the healthy gene replaces the flawed one — a feat more difficult than it sounds.
But even if the science is realized, other medical dilemmas remain, Murray says.
Genes that are responsible for fatal disorders in some people, for example, may have beneficial effects in others, according to Murray. While two copies of the sickle-cell gene brings on the deadly disease, having one copy appears to protect against malaria. “If you live in a malaria-infested area, are we harming you by eradicating that gene?” he asks.
On the other hand, not fixing the genetic flaw in disorders such as Huntington’s disease would be morally absurd, Murray says.
WHAT’S DESIRABLE? WHAT’S NOT?
But it’s the ethics of germ-line therapy that are drawing the most scrutiny. Even if the science is someday perfected, who decides what genes are worth having? What is a desirable trait?
If germ-line therapy was available in Victorian times, scientists might have decided to do away with an “emotional” gene (should one have been known), Murray says. “The human trait would be truncated and all of us emotionally impaired forever.”
In the end, it’s the unforgiving nature of germ-line therapy that has ethicists most concerned.
“Are we wise enough to tinker not just with one life, but with the lives of all that person’s descendents?” Murray asks. “That’s a pretty heavy moral burden to bear.”
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