Science gives parents some control over their children's genes

NEW YORK

hey held a news conference not long after Adam Nash was born.

It was a small affair compared to the international media extravaganza that attended last month's alleged birth of the world's first cloned human.

Maybe that's because Adam's birth had nothing to do with UFO cults, virgin births or secret laboratories in unnamed countries. But unlike the allegedly cloned "Eve," Adam offers a very real glimpse into the future of human reproduction.

For one thing, Adam has actually been proven to possess the genes he was designed with. Even more important, those genes were not merely copied from another person's, but selected to give Adam specific traits.

"Cloning is a red herring," says Princeton University biologist Lee Silver, whose 1997 book "Remaking Eden" envisions a future time when parents will have the opportunity to fiddle with their children's heredity.

Silver explains that two powerful scientific fields are just beginning to collide in a way that will profoundly change human reproduction. As reproductive technologies are developed and refined, science's knowledge of human genetics is also exploding.

The combination of genetic knowledge with reproductive technology already allows parents to select some of the genes they pass to their children. Someday it may even enable the creation of human genes, and traits, that have never existed. It is possible that our children's children's children will be engineered to live longer and be healthier, stronger and more intelligent than any generation before them.

Adam Nash's parents already had one child when he was born in August 2000. Their daughter Molly suffered from a rare genetic disease called Fanconi anemia. The Nashes wanted to make sure Adam would not also inherit the genetic defect that caused his sister to be born with a host of birth defects, including missing thumbs and hip sockets.

But they also wanted to be sure Adam would share one of Molly's genetic characteristics. Because their daughter would die without a bone-marrow transplant, the Nashes wanted their children to have the same tissue type so Adam could serve as Molly's donor.

With the help of Dr. Yury Verlinsky, a geneticist at the Reproductive Genetics Institute in Chicago, the Nashes created several dozen embryos by in vitro fertilization and chose one with the proper genetic characteristics.

That embryo became Adam.

Verlinsky doesn't modify the embryos he implants. He merely creates a number of embryos by in vitro fertilization, screens them for some desired property -- usually the absence of a particular genetic defect -- then implants the one that best fits the criteria.

So far parents have used the procedure, which is known as PGD (for preimplantation genetic diagnosis) only as a means of preventing inherited diseases in their children.

Using the technology as an enhancement to make children taller or smarter is impractical, partly because PGD merely selects among genes the two prospective parents already possess. That means Junior's height and intelligence are limited by his parents' genetics.

Verlinsky dismisses critics who accuse him of playing God, of creating "designer babies" and of trying to fool Mother Nature.

But what if scientists really could simply insert whatever genes they wanted into an embryo's DNA?

In animals, they can. But inserting genes into embryos is a highly imperfect technology. For every individual mouse or cow that picks up the inserted gene and properly incorporates it into its own DNA, there are many more that don't. And because researchers have little control over where the new DNA will end up in the animal's genetic code, in many cases it ends up causing birth defects or preventing the animal from ever being born at all.

Parents would not embrace a technology that produced far more failures and defectives than enhancements. But in the future, many of the technical obstacles to genetic enhancement are expected to fall. What then?

"My view is that certain pathways shouldn't be taken," says Stuart A. Newman, a professor of cell biology and anatomy at the New York Medical College. "I would actually advocate a ban on genetic engineering of human embryos."

Most researchers believe it will be decades before doctors slip genes into human beings as easily as we load programs onto home computers today from CD-ROMs. But when they do, the sky will be the limit.

When that day comes, says University of Minnesota bioethicist Jeffrey Kahn, it would behoove us to have thought about which modifications are socially acceptable and which are not. "We'll have to confront these questions about modification that don't have anything to do with disease," Kahn says.

The latest cloning brouhaha may amount to no more than a silly hoax, Kahn says, but it has raised issues that deserve consideration.