The DNA of an embryo has been edited for the first time in the US.

A team at Oregon Health and Science University (OHSU) used the CRISPR-Cas9 gene-editing technology to alter the genomes of a large number of one-cell embryos, which were not allowed to develop for more than a few days to avoid ethical concerns.

Human embryos have already been modified on a number of occasions in China, but the US scientists claim their approach avoids mistakes made in other labs.

While significant ethical questions have faced this kind of research at every turn, there is also a moral duty to correct DNA mutations in embryos that are known to cause severe diseases.

However, given that the genetic make-up of the offspring of all future generations would be changed, it is vital to demonstrate that there are no unwanted mutations that occur alongside the correction.

OHSU lead researcher Shoukhrat Mitalipov has given almost no details on what his team actually did, because the papers have not yet been peer-reviewed and published, but he did say that he and his colleagues were able to avoid errors made in previous studies.

The previous Chinese studies contained some CRISPR-caused editing errors, including that the desired DNA changes were only taken up by some of the cells of an embryo – an effect called ‘mosaicism’.

Dr Mitalipov said his team had found ways to avoid both mosaicism and other CRISPR errors called “off-target” effects. 

It is also the latest example of one of Dr Mitalipov’s research projects pushing scientific boundaries.

In 2007, he created the world’s first cloned monkeys, in 2013, he cloned human embryos to provide patient-specific stem cells.

His latest moves come after the U.S. National Academy of Sciences supported a new level of lab research on germline modification.

The report said CRISPR should be used for the elimination of serious diseases, but not for genetic enhancements like higher intelligence.

“Genome editing to enhance traits or abilities beyond ordinary health raises concerns about whether the benefits can outweigh the risks, and about fairness if available only to some people,” said Alta Charo, co-chair of the NAS’s study committee.

Dr Fabien Delerue - Manager of the Transgenic Animal Unit and Lecturer in the Dementia Research Unit at The University of New South Wales - has reflected on what this all means.

“It was only a matter of time…. The first experiments recently carried out by Chinese scientists on human embryos using CRISPR, the revolutionary genome editing technique, sparked a worldwide reaction,” he said.

“The leaders of the CRISPR world immediately called on a moratorium in a bid to stop manipulating the genome of human embryos. It was probably already too late.

“Considering that there has not been a single species reportedly resistant to CRISPR genome editing (from bacteria to plants, mice, cattle or even monkeys) it was only a matter of time before human embryos would be tested.

“Like any other breakthrough, CRISPR technology is routinely used in so many different applications, for so many different purposes, that it is nearly impossible to keep up with the scientific publications.

“One should consequently not be surprised that the genetic modification of the human embryo be the ultimate goal.

“Should we rejoice, or rather be terrified? The answer certainly does not lie in the power or the limitations of CRISPR.

“These are studied and perfected on a daily basis by scientists around the world. This is what we do in our lab in cells or in animals such as mice, like many others labs in Australia.

“What we should consider now, more than ever before, is 'what do we use CRISPR for when it comes to human beings'?

“The answer will certainly not be an easy one, but it will draw the lines of future CRISPR applications in humans.

“Take for example the concept of 'designer babies'. If you bluntly question people around you about the possibility of 'designing' babies, an overwhelming majority would find the idea horrifying, probably as a reminiscence of the abject Nazi endeavours that justified eugenics.

“However, when asked to consider whether genetic manipulation of the human embryo should be allowed to prevent terrible debilitating and terminal childhood conditions, the answers are somewhat different.

“For now, it is very hard to judge what the latest study in the US will bring, since no-one should speculate whilst the publication is pending. But surely it is time to start asking: what do we want to do with CRISPR, and what do we want to do with ourselves?”