(The Atlantic) – Deb Jenssen never wanted her children to suffer from the disease that killed her brother at 28. The illness, Duchenne muscular dystrophy, initially manifests in childhood as trouble with strength and walking, then worsens until the heart or the muscles controlling the lungs stop working. She decided to get pregnant using IVF so that she could select embryos without the mutation for the disorder. But when she ended up with just two viable embryos—one with the mutation—the clinic urged her to transfer both.

The embryos were female, and Jenssen remembers the doctors assuring her that, because the Duchenne mutation is linked to the X chromosome, a girl who carried it would have a backup chromosome, with a working copy of the affected gene, and would be as healthy as Jenssen was. (Read More)