News that scientists have for the first time genetically altered a human embryo is drawing fire from some watchdog groups that say it's a step toward creating "designer babies."

But an author of the study says the work was focused on stem cells. He notes that the researchers used an abnormal embryo that could never have developed into a baby anyway.

"None of us wants to make designer babies," said Dr. Zev Rosenwaks, director of the Center for Reproductive Medicine and Infertility at NewYork-Presbyterian/Weill Cornell Medical Center.

The idea of designer babies is that someday, scientists may insert particular genes into embryos to produce babies with desired traits like intelligence or athletic ability. Some people find that notion repugnant, saying it turns children into designed objects, and would create an unequal society where some people are genetically enriched while others would be considered inferior.

The study appears to be the first report of genetically modifying a human embryo. It was presented last fall at a meeting of the American Society for Reproductive Medicine, but didn't draw widespread public attention then. The result was reported over the weekend by The Sunday Times of London, which said British authorities highlighted the work in a recent report.

Rosenwaks and colleagues did the work with an embryo that had extra chromosomes, making it nonviable. Following a standard procedure used in animals, they inserted a gene that acts as a marker that can be easily followed over time. The embryo cells took up the gene, he said.

The goal was to see if a gene introduced into an abnormal embryo could be traced in stem cells that are harvested from the embryo, he said. Such work could help shed light on why abnormal embryos fail to develop, he said.

No stem cells were recovered from the human embryo, said Rosenwaks, noting that abnormal embryos frequently don't develop well enough to produce them.

Marcy Darnovsky, associate executive director of the Center for Genetics and Society, said the Cornell scientists were developing techniques that others might use to make genetically modified people, "and they're doing it without any kind of public debate."

A London-based group called Human Genetics Alert similarly criticized the work.

But Kathy Hudson, director of the Genetics and Public Policy Center in Washington, D.C., said she's not troubled by the work. She said the idea of successfully modifying babies by inserting genes remains a technically daunting challenge.

"We're not even close to having that technology in hand to be able to do it right," she said, and it would be ethically unacceptable to try it when it's unsafe.

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On the Net:

Center for Genetics and Society: http://www.geneticsandsociety.org

Human Genetics Alert: http://www.hgalert.org

Genetics and Public Policy Center: http://www.dnapolicy.org