The emerging ability to modify human embryos in a way that gets passed on to future generations has raised alarm bells for scientists who've called for a moratorium.

In the last two weeks, statements published in the journal Nature and the journal Science by Nobel laureates and from the International Society for Stem Cell Research called for a pause on genome editing experiments on human embryos.

It's the risks associated with modifying human sperm and eggs that might have unforeseen consequences, which spurred the "uh oh" moment now, said Timothy Caufield. He holds the Canada Research Chair in health law and policy at the University of Alberta in Edmonton.

"The concern is can we use this technology in an inappropriate way to alter the genome, alter the germ line to alter our human genetic heritage," Caufield said.

In Canada, researchers can change the genetic structure of a cell that doesn't get passed on. But changes to a gene that gets passed on are banned.

Genome editing is a very powerful tool, said Edward Lanphier, one of the authors of the Nature paper and chair of the Alliance for Regenerative Medicine.

"Patient safety is paramount among the arguments against modifying the human germ line (sperm and eggs,)" Lanphier and his co-authors wrote.

Cross a boundary?

There is a precedent to using the force of moral persuasion to press pause on certain experiments. In 1975 in Asilomar, Calif., researchers, doctors and lawyers agreed to guidelines on moving DNA between species until there was more comfort with the results and the ability to predict effects, said Alta Charo of the University of Wisconsin Law School, one of the authors of the Science paper.

More recently in the United Kingdom, there was a similar stop-and-reflect period on mitochondrial DNA replacement, the so-called three-parent baby technique.

Advances in genome editing technologies equip molecular biologists with scissors to delete genes, repair a mutation or add new DNA. Modifications to sperm and egg cells which get passed on to future generations is now technically possible.

"They could also be used to cross a boundary that heretofore collectively humanity has said we don't want to cross," Lanphier said.

Lanphier is also the president and CEO of Sangamo Biosciences in Richmond, Calif., which is conducting clinical trials to evaluate genome editing as a "functional cure" for HIV by modifying the immune system's T cells.

It's the combination of technological advances and rumours of human embryo experiments that's sparked the urgency.

"I think it's more than just rumours," Lanphier said. "It's a broad-based perception that these papers are pending publication."

The pending publications show genome editing technologies can be used in human embryos and it does change the germ line, he said.

The Science and Nature papers differ on whether to allow basic research on human embryos to continue.

What's agreed is this is a critical moment for experts to come together to discuss the technology and reach a collective decision on how or if we want the technology applied to engineering the human genome.

Charo welcomes discussion among scientists and the public on applications of the technology.

"I think that is very reassuring and it moves people back to exalting the scientists and away from thinking of them as Dr. Frankenstein," Charo said.