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Screening Embryos for Disease

Jenifer and Angelo Magliocco of Trumbul, Conn., know much more about spinal muscular atrophy than they ever wanted to. The rare genetic disease killed their first son, Angelo James, when he was just 8 weeks old.

As the name suggest, the illness causes muscles to stop functioning. In its most severe form, death comes within weeks of birth.

The Maglioccos wanted to have another child, but they didn't want another one afflicted with the disease. In the past, that might have meant testing a fetus and, if the disease were present, having an abortion. But now there's an alternative: preimplantation genetic diagnosis.

"Preimplantation genetic diagnosis is essentially a method that we have for testing very early human embryos for specific genetic disorders," says Dagan Wells, a Yale University geneticist.

When the Maglioccos learned from their genetic counselor that PGD was available, they decided to try it.

In order to get PGD, the Maglioccos first had to undergo in vitro fertilization.

In November, Jenifer Magliocco started taking drugs that would cause her body to make more than a dozen eggs, rather than the usual one per month.

Just after Thanksgiving, doctors removed her eggs and mixed them with her husband's sperm.

"After three days, they formed embryos which are usually composed of between six and 10 cells," says Wells. "At that point, what you can do is take away just one of those cells from the embryo without causing any significant damage to it."

A single cell from each embryo was sent to Well's lab. The rest remained in an incubator at the fertility clinic.

At the lab, Wells tests the DNA from each embryo to see which has a mutated version of the spinal muscular atrophy gene.

Earlier this month, Wells made his diagnosis. As the Magliocco's waited anxiously in a fertility clinic across town, Wells put the DNA on a gel-like substance that causes the samples to separate into bands.

Peering at the Maglioccos' sample, Wells can see that embryo No. 4 has the mutated gene, and embryo No. 12 also likely has the gene.

"The others look like they're fine," he says. Wells tells the clinic which embryos are safe to transfer. The clinic will transfer two or three of those embryos to Jenifer's womb. The rest will be frozen for future use.

There's no guarantee Jenifer will get pregnant using this technique. But at least she can be certain that if she does, the child won't have the disease that killed her first son.

While many people would agree it's ethical to not implant embryos carrying a gene for a fatal illness, PGD is also being used for more ethically contentious purposes. Consider the case of Chad Kingsbury and his wife, Colby. Chad carries a gene that vastly increases his risk of colon cancer. The gene is rampant in his family, and many of his relatives have died from colon cancer. The Kingsburys wanted children, but were desparate not to saddle them with this genetic blight, so they used PGD to select embryos that didn't have the gene.

But Chad is 33 and still alive. True, he is at risk for colon cancer, but if the disease is caught early, it can be effectively treated. So the embryos the Kingsburys were choosing not to implant could have produced healthy babies, albeit babies with an increased risk of cancer. Some see this as a form or eugenics. Well intentioned, but eugenics all the same.

PGD clearly represents a potentially important tool for preventing disease. But it has also opened some ethical debates.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

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Joe Palca is a science correspondent for NPR. Since joining NPR in 1992, Palca has covered a range of science topics — everything from biomedical research to astronomy. He is currently focused on the eponymous series, "Joe's Big Idea." Stories in the series explore the minds and motivations of scientists and inventors. Palca is also the founder of NPR Scicommers – A science communication collective.