Powerful gene editing procedures could one day be allowed to prevent people from passing on serious medical conditions to their children, according to a major report from senior US researchers.

The cautious endorsement from two of the most prestigious US science institutions means that human embryos, sperm and eggs could all be genetically manipulated to mend faulty genes which are known to cause serious disease or disability, once research has shown it is safe to do so.



What is Crispr? Crispr, or to give it its full name, Crispr-Cas9, allows scientists to precisely target and edit pieces of the genome. Crispr is a guide molecule made of RNA, that allows a specific site of interest on the DNA double helix to be targeted. The RNA molecule is attached to Cas9, a bacterial enzyme that works as a pair of "molecular scissors" to cut the DNA at the exact point required. This allows scientists to cut, paste and delete single letters of genetic code.

The report from the National Academy of Sciences and the National Academy of Medicine says the procedure is “highly contentious” because any genetic changes that are made are then inherited by the next generation. “The technology would therefore cross a line many have viewed as ethically inviolable,” it states.



Most scientists agree that far more work is needed before clinical trials of so-called “germline” therapies can begin in humans. But the report argues that if the procedure is found to be safe and effective in the years ahead, it should not be ruled out in exceptional cases.



“We have identified a very strict set of criteria which, if satisfied, could make it permissible to start clinical trials,” said Alta Charo, co-chair of the report committee and professor of law and bioethics at the University of Wisconsin–Madison. While gene editing is unlikely to affect the prevalence of diseases any time soon, it could provide some families with their best hope for having healthy children.



According to the report, human embryos, sperm and eggs should only be considered for gene editing to prevent serious conditions and when no other alternative is available. To go ahead, scientists would have to be confident they could stop a disorder by rewriting the DNA in a faulty gene to make it into a healthy version already found in the population.



The report stresses the need for a stringent oversight system for any such trials to make sure scientists, patients and the broader public understand the risks and benefits, and to come down hard on any clinics that offer treatment for less serious disorders or for human enhancement.



“There is an enormous amount of research that has to go into this, and then the question is what are the conditions where you’d even consider it, and those are very tightly defined,” said Rudolf Jaenisch, a member of the report committee and professor of biology at MIT. “It would be conditions where no other options exist to have a healthy baby.”



Genome editing: how to modify genetic faults – and the human germline Read more

One example is when an adult carries two copies – rather than one – of the gene that causes Huntington’s disease, a devastating condition that steadily damages nerves in the brain. If that person has children they will inherit at least one copy and will develop the disease. With gene editing, harmful copies could potentially be fixed in the parent’s sperm or eggs, or in any embryos created through IVF.



Under British law, gene edited embryos, or embryos made with genetically engineered sperm or eggs, cannot be implanted into a woman. The only exception, endorsed by parliament in 2015, is for a procedure called mitochondrial transfer, which aims to prevent women from passing on genetic diseases to their children. In the US, the Food and Drug Administration is currently not allowed to consider applications for germline therapy clinical trials, but the temporary restriction is only in place until April this year.



The national academies’ report comes at a time when scientists are making spectacular progress in genome editing. With the latest gene editing tool, named Crispr-cas9, scientists can alter single letters of the DNA code, or rewrite whole genes. The technique has given researchers unprecedented insights into the basic biology of development and cancer, but has also been tested in animals as a treatment for a wide range of diseases. Last year, a Chinese group became the first to launch a trial of Crispr-cas9 to treat patients with aggressive lung cancer for whom all other therapies had failed.



In separate research published in Nature Communications on Wednesday, scientists at the University of Washington in Seattle used gene editing to rewrite faulty genes responsible for Duchenne muscular dystrophy in adult mice. “We’re a long way from clinical application but there’s no doubt that the results of this study are exciting,” said Darren Griffin, a geneticist at the University of Kent. Other studies reporting progress with different diseases emerge at least every month.



Summit rules out ban on gene editing embryos destined to become people Read more

The national academies’ report goes on to back the use of genome editing to correct faulty genes in adult tissues, such as the liver, lungs and heart, where the changes will not be passed on to children. But while it recommends that the tool is used only to prevent and treat diseases and disabilities, the report points out that in the future, the same interventions could potentially enhance people’s natural abilities. For example, a gene editing therapy that boosts the muscles of patients with muscular dystrophy could perhaps be given to healthy people to give them superhuman strength. “We need an ongoing public conversation about how much value we place on some of these so-called enhancements,” said Charo. “Until we know that, we can’t know how to value them against the risks.”



Even the academies’ heavily-caveated endorsement of gene editing will raise fears of a “slippery slope” that leads to a society of genetic haves and have-nots. But Richard Hynes, a report chair and cancer researcher at MIT, said that regulations could effectively block the use of the tools for enhancement. “The slope is not very slippery. Friction is introduced by the regulatory system,” he said.

Charo ruled out the use of gene editing to boost people’s intelligence, which is thought to be influenced by hundreds, if not thousands, of genes. “We have no idea how to define intelligence, let alone how to manipulate it genetically,” Charo said. “It’s one of the examples that is raised all the time, but it’s one of the least likely to be relevant, because we don’t have a clue how we’d do that.”