Could editing the DNA of embryos with CRISPR help save people who are already alive?

Amid last year’s backlash against the birth of the world’s first genetically edited babies, some experts preached prudence: Editing the genomes of embryos, they argued, could one day “cure” people of diseases before they’re even born.

But there is another, less-discussed potential application of editing an embryo: tweaking its DNA to help save someone who is already alive.

Take the case of Jessica and Keith, a couple in the Bay Area with a 2 1/2-year-old daughter with Fanconi anemia, a genetic disease that leads to the failure of bone marrow to produce red and white blood cells and carries an increased risk of a number of cancers. The best treatment is a stem cell transplant from a sibling, and Jessica and Keith, who asked that their last name not be used, are now in the process of trying to have another child through IVF who can serve as a donor — what’s known as a savior sibling.

But making an embryo that’s both healthy and a suitable donor “match” for the older sibling is an exercise in long odds. It’s theoretically possible that altering an embryo’s DNA with the genome-editor CRISPR could improve