The experiment was just an exercise in science — the embryos were not allowed to develop for more than a few days and were never intended to be implanted into a womb, according to MIT Technology Review, which first reported the news.

Officials at Oregon Health & Science University confirmed Thursday that the work took place there and said results would be published in a journal soon. It is thought to be the first such work in the U.S.; previous experiments like this have been reported from China. How many embryos were created and edited in the experiments has not been revealed.

The Oregon scientists reportedly used a technique called CRISPR, which allows specific sections of DNA to be altered or replaced. It's like using a molecular scissors to cut and paste DNA, and is much more precise than some types of gene therapy that cannot ensure that desired changes will take place exactly where and as intended. With gene editing, these so-called "germline" changes are permanent and would be passed down to any offspring.