Researchers in Portland, Oregon have used a powerful gene editing tool called CRISPR to create genetically modified human embryos, MIT Technology Review reported on Wednesday in an exclusive. This is the first confirmed case of the gene editing of human embryos in the US, and gets scientists closer to the ability to create genetically engineered humans.

First, a little background. CRISPR, which is often compared to the cut-and-paste function on a word processor, is a powerful and comparatively new genetic engineering technique that allows scientists to make specific, targeted changes to the DNA of a plant, animal, or human.

Relatively cheap and easy to use, scientists say they can potentially wield this powerful tool to cure a range of diseases, like HIV and muscular dystrophy. Some experiments, though, have raised eyebrows—in 2015, scientists in China used it to make extremely muscled beagles—and ethicists have been warning about adopting gene editing too rapidly in humans. The fact that it's so easy to use has made plenty of people uneasy: The US intelligence community warned in 2016 that gene editing is a potential weapon of mass destruction.

Beyond the often-stated fear that gene editing will lead to a world of designer babies and "genetic have-nots," CRISPR is still new and may have consequences we don't understand.

Read More: We Risk Programming Inequality into Our DNA

Plenty of countries have some kind of a ban on gene editing in human embryos, although as the use of CRISPR speeds up in the lab, regulations and viewpoints are evolving. Earlier this year, the US National Academy of Sciences said that editing the DNA of human embryos could be allowed in order to cure disease, with certain safeguards in place.

Scientists are pressing ahead. Teams in China have edited human embryos at least three times. Earlier this year, a Chinese team reported another first: using CRISPR to correct genetic mutations in three normal human embryos. (Previous tests were done on non-viable embryos that couldn't have produced children. According to Technology Review, the US experiment destroyed embryos after a few days, with no intention to implant them.)

Scientists in the US watched developments in China "with a combination of awe, envy, and some alarm," Technology Review reported. Apparently they were eager to try it themselves.

This latest gene editing effort was led by Shoukhrat Mitalipov of Oregon Health and Science University, who was also behind the world's first cloned monkeys in 2007. Mitalipov declined to comment to Technology Review, and said the results are pending publication in a scientific journal. Mitalipov didn't immediately respond to an email requesting comment from Motherboard.

Technology Review couldn't confirm in its report which disease genes were targeted here, although one source told the publication that "many tens" of embryos were made from sperm donors with inherited disease mutations. The US experiment seems to have improved on earlier results from China, where CRISPR caused editing errors and worked imperfectly, being taken up by only some cells. An anonymous source called it a "proof of principle" in the report.

Scientists who are applying CRISPR have an excellent argument for doing so—who could resist a technology with the potential to cure so much death and disease?

But science doesn't happen in a vacuum, and even the noblest of intentions could drive us somewhere that we never intended. Experiments from Mitalipov and others pave the way for a future where we can cure an array of terrible afflictions, but also hold the real possibility of creating "designer" humans, and programming inequality deeper into our DNA.

There are plenty of legal barriers in places like the US that would prevent the creation of a genetically engineered baby. But that isn't true in every country. We're getting better at using this tool, so it isn't a question of if it will happen, but when. As Technology Review notes, "the creation of a gene-edited person could be attempted at any moment."