In early August, researchers announced they had genetically edited human embryos, the first such experiment reported in the United States.

In an article, published in the journal Nature, scientists revealed that CRISPR — a type of “molecular scissors” — could be used to switch a mutated gene from one parent for a healthy gene inherited from another parent. (The embryos, created in a lab dish, were destroyed after several days, as planned.)

It’s a tiny tweak that could someday save lives — as the study’s authors note, more than 10,000 medical conditions are caused by inherited genetic mutations. In the test embryos, researchers eliminated a mutation that causes hypertrophic cardiomyopathy, a dangerous heart condition. But the study has reignited concerns from some about the ethics of heritable (germ line) human gene-editing, not least the creation of “designer babies” using a mix of perfect genes.

Shoukhrat Mitalipov directs the Center for Embryonic Cell and Gene Therapy at Oregon Health and Science University and co-authored the new study. The way he explains it, designer babies would be difficult to produce using the technique: “At this point, it seems like you would have to do something differently if you want to insert some extra piece of DNA — and the embryo seems likely to refuse it,” he says.

In the study, the researchers focused on a heterozygous gene mutation given to the embryos by just one parent — the sperm-donor father. (The eggs came from multiple healthy donors.) After using CRISPR to slice the mutated gene out, Mitalipov explains, the team gave the embryos a healthy synthetic gene to copy. But they didn’t use it. Instead, “The embryos always chose that maternal normal gene as a blueprint to repair the damaged paternal gene,” he says. “So, this was quite different and unexpected.”

The technique still needs more work to improve its efficacy: According to Mitalipov, most, but not all of the embryos were able to repair themselves. And even with improvements, the method won’t head to human clinical trials anytime soon, at least not in the United States. Congress has banned the Food and Drug Administration from considering clinical trials that involve germ-line changes to human embryos. (And, the National Institutes of Health do not fund embryonic gene-editing research; the CRISPR study was funded by outside organizations.)

A day after the CRISPR study went live, an international working group published its own research on heritable genetic editing in humans. In the position paper, genetic experts warn against allowing gene-edited embryos to develop in pregnancy, at least for now, and suggest gene-editing technology should be considered only as a last resort in the future. But the authors give cautious support for in vitro human germ-line research (like the preliminary CRISPR study) and suggest public dollars be used to fund it.

“The main point of our statement was that basic science research like this at quite early stages is appropriate if it’s done in a regulated manner with good oversight and transparency,” says lead author Kelly Ormond, a genetics professor at Stanford University School of Medicine and faculty member at the Stanford Center for Biomedical Ethics.

In the paper, Ormond and her co-authors argue that public funding can actually drive oversight and transparency in genome-editing research — and keep ethically sensitive experiments from moving to countries that may do less to regulate them.

“I think the main issue is that not every country in the world has the same sorts of regulations or the same ability to enforce regulations,” Ormond says. “So, we really felt quite strongly with our statement, which was signed by 11 international organizations across five continents, that we need to get everybody around the globe talking about this so that it happens in parallel with the science that’s going on — so that in five years we’re not all of a sudden surprised by what’s happening and caught off guard with no policies.”

Meanwhile, Mitalipov and his team are considering the way ahead with their research. “The intention of doing research on human embryos is, it has to be for [the] sake of future treatments,” he says. “And we would be happy to move forward and work with the FDA particularly because defining what the next step and the safety, efficacy studies that need to be done — you know, the FDA usually regulates it.”

But at this point, he says, “we wouldn’t know how to move forward.”

This article is based on an interview that aired on PRI's Science Friday with Ira Flatow.