A 27-year-old woman in the United States, had undergone genetic testing that showed she had inherited a gene that put her at risk for Gerstmann-Strussler-Scheinker (GSS) syndrome, a rare and fatal brain disorder seen in only a few families in the world, Fox News reports. Symptoms of the condition usually appear between ages 35 and 55, and include progressively worsening speech, movement and memory problems.

To have children, the woman and her husband used IVF, an assisted-reproduction technique in which eggs from the mother are fertilized in a laboratory. But before implanting the embryos in the uterus, doctors took an extra step and screened the embryos for the GSS genetic mutation.

Six out of the 12 embryos were mutation free, and the couple chose to implant two embryos. Both embryos implanted successfully, and the woman gave birth to twins after nearly 34 weeks of pregnancy.