Now that science is allowing us to tweak our genes, how far will we take it? Are custom-made babies truly on the horizon?

Three-parent babies—the headlines could almost be mistaken for science fiction. But according to a British health agency, a new technique could prevent mitochondrial disease (which is passed down from a mother to her children) by creating infants with three parents. The strategy involves using genetic material from two women and one man to generate a healthy embryo.

Annually, about 1,000 to 4,000 Americans are born with mitochondrial diseases, which are incurable.

Robin Lovell-Badge of the Medical Research Council says it will take about two years to test the technique in the U.K.; Britain’s Human Fertilisation and Embryology Authority says that evidence does not show the technique is unsafe.

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In the U.S., the Food and Drug Administration (FDA) reviewed the matter and opened it up for comments earlier this year, sparking debates about genetic tweaking.

Bonnie Steinbock, Ph.D., a professor at the University of Albany, who attended the meeting in February, explained one objection to mitochondrial transfer: the resulting child will have three genetic parents—the provider of sperm, the provider of nuclear DNA, and the provider of mitochondrial DNA.

“While many of us today may find the idea of designer babies to be morally repugnant, that could well change a generation from now.”

“I’m not sure why this is, on the face of it, problematic,” Steinbock said, who notes that assisted reproduction has already introduced the notion of multiplied parents. A child can already have a genetic father and mother, as well as a gestational mother. That same child could also have two rearing parents that may not be biologically related. “Adding one more parent into the mix does not seem to change things radically,” she says.

Mitochondrial transfer isn’t the only genetic breakthrough that is raising eyebrows.

David Kingsley, a professor at Stanford University and investigator at Howard Hughes Medical Institute, recently led a study, published in Nature Genetics, that uncovered a single letter change in the human genome that results in blonde hair. With that kind of information—and the potential to change it—medical science is perhaps ready to produce designer babies, in theory.

Kingsley noted that his study has nothing to do with trying to genetically engineer traits in humans; the scientists wanted to understand where traits come from and find better ways to study them.

“The findings from mice may eventually suggest new ways to address the causes or symptoms of a disease in humans, but the human applications will come from applying the insights from basic research, not by trying to engineer the DNA sequence of the human genome,” he said.

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Professor Robert Winston, one of Britain’s leading fertility doctors, recently unveiled a genetic engineering technique that makes it possible to splice new genes into sperm. The move is aimed at creating pigs with enough human DNA in them so that humans cannot reject their organs during a transplant.

Both of these breakthroughs may not be aimed at designing humans, but they fuel the designer baby debate. When should and shouldn’t advancements in science be used in genetics?

Dr. Kiran Musunuru, Ph.D., with the Harvard Stem Cell Institute in Boston, said that there are no longer any technological bars to genome editing—only moral and ethical ones. When IVF first came into the picture in the 1970s, it was quite controversial, but hardly anyone thinks of it that way now.

“Nowadays, almost nobody thinks twice about it. So while many of us today may find the idea of designer babies to be morally repugnant, that could well change a generation from now,” he said.

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The Designer Baby Debate

Dr. Robert Klitzman, who heads up the Masters of Bioethics program at Columbia University, said that sometimes the same advances that can alleviate diseases cause ethical dilemmas. Some parents may want to select the gender of their child, or say they don’t want a child with a mutation that raises the risk of breast cancer, for example. These traits could range from changing the color of the child’s hair to pinpointing the baby’s intelligence level.

“These questions are difficult because they pit the freedom of future parents to do what they want against concerns that some other people have that manipulating the genes of future generations is immoral or dangerous,” Klitzman said. “Eugenics—the effort to make better genes—has led to horrific results, most notoriously with the Nazis.”

There are many good uses of this technology that should be pursued, he said. But parents, health care providers, and the public at large will have to come together to determine if, and where, the limits should be placed.

“The more informed discussion we have about these issues, the better off we will all be,” Klitzman said.

Dr. Alan Copperman, the director of the Division of Reproductive Endocrinology at Mount Sinai Medical Center in New York said that research needs to be transparent as scientists usher in the next era of genomic medicine. Also, he said, any innovations should be performed with safety for individuals—and society—in mind.

Experts are mum on how soon designer babies will be a reality. For now, they want to weigh the advantages and disadvantages of such discoveries by focusing on the science. The ethical questions, however, loom in the background.

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