A group of senior American scientists and ethics experts is calling for debate on the gene-engineering of humans, warning that technology able to change the DNA of future generations is now “imminent.”

In policy recommendations published today in the journal Science, 18 researchers, including two Nobel Prize winners, say scientists should accept a self-imposed moratorium on any attempt to create genetically altered children until the safety and medical reasons for such a step can be better understood.

The concern is over a rapidly advancing gene-editing technology, called CRISPR-Cas9, which is giving scientists the ability to easily alter the genome of living cells and animals (see “Genome Surgery”). The same technology could let scientists correct DNA letters in a human embryo or egg cell, for instance to create children free of certain disease-causing genes, or perhaps with improved genetics.

“What we are trying to do is to alert people to the fact that this is now easy,” says David Baltimore, a Nobel Prize winner and former president of Caltech, and an author of the letter. “We can’t use the cover we did previously, which is that it was so difficult that no one was going to do it.”

Many countries already ban “germ line” engineering—or changing genes in a way that would be heritable from one generation to the next—on ethical or safety grounds. Others, like the U.S., have strict regulations that would delay the creation of gene-edited children for years, if not decades. But some countries have weak rules, or none at all, and Baltimore said a reason scientists were speaking publicly now was to “keep people from doing anything crazy.”

The advent of CRISPR is raising social questions of a kind not confronted since the 1970s, when the ability to change DNA in microӧrganisms was first developed. In a now famous meeting in 1975, in Asilomar, California, researchers agreed to avoid certain kinds of experiments that were then deemed dangerous. Baltimore, who was one of the organizers of the Asilomar meeting, says the scientists behind the letter want to offer similar guidance for gene-engineered babies.

The prospect of genetically modified humans is surprisingly close at hand. A year ago, Chinese researchers created monkeys whose DNA was edited using CRISPR (see “10 Breakthrough Technologies 2014: Genome Editing”).

Since then, several teams of researchers in China, the U.S., and the U.K. have begun using CRISPR to change the DNA of human embryos, eggs, and sperm cells, with an eye toward applying the technology at in vitro fertility (IVF) clinics. That laboratory research was described by MIT Technology Review earlier this month (see “Engineering the Perfect Baby”). 

Last week, in Nature, representatives of an industry group, the Alliance for Regenerative Medicine, recommended a wider moratorium that would also include a cessation of such laboratory studies, which it termed  “dangerous and ethically unacceptable” (see “Industry Body Calls for Gene-Editing Moratorium”).

But that position was rejected by the authors of the current Science editorial. Instead, they said basic research on germ line engineering should move forward, including efforts to determine “what clinical applications, if any, might in the future be deemed permissible.”

Today’s statement was organized by Jennifer Doudna, a University of California, Berkeley, biologist who codiscovered the CRISPR technology. She confirmed that the group supports using it to edit the DNA of early-stage human embryos if it’s for scientific research.

That recommendation could come as a bombshell to critics of germ line engineering, as well as religious groups. Some believe an ethical “bright line” should separate humanity from the kind of gene-tinkering used on plants, microbes, and animals. If so, what is the point of testing the technology in human embryos?

But some authors of the Science editorial believe basic research must be given a free hand. “Science should not be impeded in its earliest stages by concerns that improvements in, and validations of, certain parts of the technology are opening the door to eugenics,” says Paul Berg, a professor emeritus at Stanford’s medical school, who also signed the letter. Berg said he supported research aimed at “perfecting the technology in preparation for the time when society could sanction germ line modification in medicine.”

A growing industry has already sprung up around gene editing, which is being applied to lab animals and farm species, and is being contemplated as a way to treat adults with diseases like muscular dystrophy or HIV infection. Such treatments of sick individuals are known as somatic gene therapy, and were not the subject of the current editorial, or the call for a moratorium.

Theoretically, germ line editing could correct genes that lead to lethal diseases before birth. For instance, if a person had Huntington’s disease, caused by a single faulty gene, CRISPR could be used to eliminate the mutation from that person’s children.

One biotechnology company, OvaScience of Cambridge, Massachusetts, has invested more than $2 million dollars investigating whether gene-editing could be used in IVF procedures. OvaScience did not respond to a request for comment.

While correcting inherited disease genes could prove medically useful, the authors of the Science editorial said much remained unknown. “Even this seemingly straightforward scenario raises serious concerns,” they said of editing disease genes back to their healthy form. That is because scientists are unable to predict all the consequences of changing DNA letters in a person, especially if multiple genes were corrected at once.

“You would be making changes in generations to come, in ways that are very hard to predict,” says Baltimore.

In their editorial, the researchers call for high-level technical forums to discuss CRISPR, as well as convening a “globally representative” group of government agencies, ethics experts, and scientists to recommend policies. In the meantime, they say, scientists must refrain from actually producing genetically engineered babies, even though the opportunity to do so now exists.

“Scientists should avoid even attempting, in lax jurisdictions, germline genome modification for clinical applications in humans,” they write.