When it comes to CRISPR, questions about if we can edit human embryos are fast giving way to discussions more focused on “But should we?” and “When?” as feats with the gene-editing technology have started to accrue.

Today, biologists from Oregon report in Nature that they have had unprecedented successes using that gene-editing technology to alter early-stage, viable human embryos. The advance moves the field far past earlier attempts by researchers in China and underscores the need to come up with some answers—and fast, researchers say. Although the U.S. Food and Drug Administration is currently barred from granting approval to anyone hoping to use this technology in pregnancies, the Nature study suggests such work could be possible, says Jennifer Doudna of the University of California, Berkeley, a biochemist and CRISPR expert. But she and many others say this would be an inappropriate use of the technology. “I’m not categorically against all human germ-line editing,” Doudna says, “but I think there would need to be a reason to do it that would justify the risks and costs.”

The Oregon Health & Science University team edited the DNA of dozens of embryos to correct for a genetic mutation that often leads to heart failure. They then checked the edited embryos with genome sequencing and discovered that the procedure caused no apparent errors. The group also managed to almost completely eliminate mosaicism—an editing failure in which only some of the desired cells are repaired. “Those are the things everyone was concerned about in earlier embryo work,” says George Church, a CRISPR expert and geneticist at Harvard Medical School, who was not involved with the work.

The gene-editing success appears to be largely due to one procedural change: The researchers introduced the editing system—the enzyme Cas9 and a guide RNA sequence that helps the editing machinery find its target—at the same time they injected the mutation-laden sperm into a healthy egg in the lab. That allowed for much earlier editing to take place—apparently prior to any cellular replication. That’s a departure from earlier approaches by other research groups in China that had instead introduced the editing components after the egg was fertilized by sperm. “This small change in injection protocol has resulted in something better than all prior embryo work and cell culture work,” Church says.

So far, preventing disease by employing CRISPR–Cas9 to alter the human germ line—a human embryo, egg or sperm—has remained extremely controversial, due to concerns about unwittingly introducing errors or leaving stowaway unedited disease-causing mutations that would put future generations at risk of disease. And until now CRISPR had not been tried on human embryos in the U.S. But Shoukhrat Mitalipov at Oregon and his colleagues went further than the earlier Chinese works, editing dozens of embryos with much greater efficiency.

“This is a harbinger of what’s to come,” says Doudna, who also did not take part in the work. “This underscores the important discussion that needs to happen right now,” she says. George Daley, a stem cell researcher and dean of Harvard Medical School agrees: “This paper establishes that we can do embryo gene editing. The question now remains should we—and for what purposes and should there be certain applications that are allowed and others that are prohibited?”

Such contentious issues were considered earlier this year by a National Academies of Sciences, Engineering and Medicine expert working group. It released guidance saying it would not be appropriate to proceed with any clinical work of human germ-line editing unless there was broad public consensus about the safety and merits of the work—something that has not been achieved. The Academies committee has noted there is still a tremendous amount of research needed before trying to move forward with something like initiating pregnancies. And this Nature paper is just the beginning of the research the report contemplated, says legal scholar and bioethicist R. Alta Charo of the University of Wisconsin Law School, who co-chaired the Academies’ committee but says she is speaking for herself and not the panel. “Understanding how gene editing works in human embryos will require research in human embryos,” because mouse embryos, for example, have species-specific developmental differences, notes Dana Carroll, a biochemistry professor at the University of Utah who researches CRISPR. (The Mitalipov team only allowed the human embryos to proceed to the blastocyst stage—when they are just a few days old—and did not attempt to implant them in a woman.)

In their study Mitalipov and colleagues edited out the MYBPC3 mutation associated with hypertrophic cardiomyopathy (HCM), a disease of the heart muscle that affects about one person in 500. Even a single copy of the mutation can result in the disorder and about 40 percent of individuals with HCM have the mutation. Right now the problematic gene can often be caught with preimplantation genetic diagnosis—screening of embryos in the lab—but using CRISPR could boost the number of usable embryos, they say. Moreover, this CRISPR technique may eventually be an important intervention in situations where parents want to have a genetically related child but have a homozygous condition—say both parents have two copies of a disease-causing mutation like that which causes sickle cell—which would result in all embryos being affected by the disorder.

There are myriad technical obstacles to overcome before CRISPR could address homozygous conditions. One big one: “Not everybody appreciates the way CRISPR technology works—it makes the cut in the DNA but it doesn’t take care of the repair—so we rely on the cells’ fundamental machinery to do that,” Doudna says. In the latest experiments the Mitalipov group focused on snipping out the mutated gene in heterozygous cells—a situation in which there was still a “good” nonmutated copy available for the natural cellular repair systems in the embryo to use as a template for repair after the researchers edited out the problematic one. But in the course of their work, the team noted a potential hiccup for CRISPR work on homozygous forms of the disorder—it may be extremely difficult to repair homozygous mutations once they are edited out because they would not have those built-in blueprints for what they should look like. In fact, the Mitalipov group found that cellular repair mechanisms, at least in their experiments, did not respond very well to the introduction of a synthetic repair template added by the researchers. According to Doudna, that suggests future homozygous work will be challenging—maybe far more so than scientists have expected.</s>(CNN) Scientists are getting one step closer to snipping inherited genetic diseases out of human offspring using a gene-editing technique called CRISPR.

For the first time, scientists said, they corrected a gene mutation linked to inherited heart conditions in human embryos using the approach. A study demonstrating the technique was published in the journal Nature on Wednesday (PDF).

Last week, the MIT Technology Review released the first news of this scientific feat, describing the research as the first-known attempt at creating genetically modified human embryos in the United States.

However, Juan Carlos Izpisua Belmonte, a co-author of the study, described it as the first in the world to demonstrate gene-editing to be safe, accurate and efficient in correcting a pathogenic gene mutation in human embryos. Previous attempts by Chinese researchers were unsuccessful at achieving this without safety concerns.

"This is the first that has been demonstrated as safe and working," said Belmonte, a professor at the Salk Institute for Biological Studies' gene expression laboratory in La Jolla, California.

"All cells of the embryo were corrected," he said. "It seems to be working from these samples that we have chosen, but we need to do much more basic research with many other genes."

The study was a collaboration between the Salk Institute, the Oregon Health & Science University in Portland and Korea's Institute for Basic Science.

Scientists estimate that more than 10,000 human diseases may result from mutations to a single gene occurring in all cells of the body, according to the World Health Organization

Cutting and correcting gene mutations

The study used 75 human zygotes in which the father carried a mutation on the MYBPC3 gene, Belmonte said. The eggs used to produce the zygotes did not carry that gene mutation. The researchers noted that they received informed consent from the donors of the eggs, sperm and embryos used in the study.

Hypertrophic cardiomyopathy also is thought to be the most common inherited or genetic heart disease in the US, according to the Centers for Disease Control and Prevention

Newly fertilized eggs before gene editing, left, and embryos after gene editing and a few rounds of cell division.

In a lab dish, the researchers used CRISPR, a gene-editing technique, to remove the harmful MYBPC3 mutation from the human zygotes. Then, the zygotes' own DNA-repair mechanism replaced what was cut out with a copy of a MYBPC3 gene from the mother, which did not carry a mutation, Belmonte said.

"A male research subject known to be heterozygous for this gene mutation was recruited for the study, as were several healthy young egg donors," Dr. Paula Amato, an obstetrician-gynecologist at Oregon Health & Science University, said Tuesday. She was a co-author of the study.

"CRISPR was introduced at the time of sperm injection," she said. "Then, DNA repair of the embryos was assessed."

The researchers found that about 72% of zygotes were properly and safely corrected on the MYBPC3 gene, Belmonte said.

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This method significantly differed from studies in which scientists used the CRISPR tool to replace what was cut out with whatever the scientists desired.

"The previous human studies done in China had very small numbers, and one of them used abnormal embryos," Amato said. "So we think this is the first, largest study from which you could draw some reasonable conclusions."

Some gene-editing attempts in human embryos have been problematic, resulting in an issue called mosaicism , in which the corrections made in one gene failed to replicate once that cell divided into two cells, those two cells divided into four cells and so on.

"So when the baby is born, all the cells do not have the mutation anymore. ... This study, it shows that we can correct the embryo and then, after the division, all the cells are corrected, so there's not what we call mosaicism," said Belmonte, who is also a member of the National Academies of Sciences, Engineering and Medicine's committee on human gene editing.

This year, the academies published a report on human genome editing that addressed potential applications of the technology, including the possible prevention or treatment of inherited diseases or conditions.

The future of gene editing

Though the researchers have expressed enthusiasm around their new study, they also noted that the findings must be replicated in followup research before this gene-editing approach can move forward to clinical trials.

"The fact that it is, apparently, a new and poorly understood mechanism and it is not the now standard CRISPR 'cut and replace' method adds to the time needed for research into its safety and effectiveness," said Hank Greely, professor of law and genetics at Stanford University, who was not involved in the new study.

Yet future research can come with some political challenges, Amato said.

"First of all, there are regulations regarding use of federal funds for embryo research, so the (US National Institutes of Health) does not currently support embryo research, so that's one barrier. The other barrier is, the (US Food and Drug Administration) is prohibited from considering any clinical trials related to germline genetic modification," she said.

In this new study the embryos were only allowed to mature to day three after fertilization before they were disaggregated, or isolated into various components, for further analysis.

In the far-off future, a clinical trial could include transplanting corrected embryos into a uterus with the goal of establishing pregnancy and then monitoring the embryos as they develop into children.

Still, "it is way too early to contemplate implanting the edited embryos for the purpose of actually establishing a pregnancy," said Dana Carroll, a professor of biochemistry at the University of Utah who was not involved in the new study but has used CRISPR in his own research.

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"The genome editing tools are currently not sufficiently efficient and specific to be reliable, and regulatory and oversight processes have not been established," Carroll said, adding that the work on the new study was "well-done" and "well-presented."

"The authors have made an important discovery regarding the repair of CRISPR-induced DNA breaks in human eggs just at the time of fertilization," he said.

"This information will help to guide ongoing research, and it demonstrates that research on early-stage human embryos will be necessary to establish safe and effective procedures in the long run," he said. "There is still a lot of work to do to understand repair processes in very early embryos and to optimize the use of the CRISPR reagents, but this study makes a valuable contribution."

Some CRISPR critics have argued that gene editing may give way to eugenics and to allowing embryos to be edited with certain features in order to develop so-called designer babies

However, the researchers wrote in their study that they hope CRISPR could be considered as an alternative option to preimplantation genetic diagnosis, also known as PGD, for couples at risk of passing on an inherited disease.

'This opens up the possibility for those embryos'

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When only one parent carries a heterozygous mutation on a gene, about half of the embryos from that parent should be mutation-free while the others would have the mutation. Selectively, the parents' doctor would chose the healthy embryos to be implanted and discard the embryos with the mutations, Belmonte said.

Sometimes, "a couple that wants to have a baby and they have a mutation, they may not have enough embryos to choose from," he said. This is when CRISPR can come in.

"This technology, independent of the embryos that are there, it would go on and correct all of them. ... This opens up the possibility for those embryos," he said. "That's important because after the first implantation, if it doesn't work, you can do it again."

The researchers wrote in their study, "PGD may be a viable option for heterozygous couples at risk of producing affected offspring. In cases when only one parent carries a heterozygous mutation, 50% of embryos should be mutant. In contrast, targeted gene correction can potentially rescue a substantial portion of mutant human embryos, thus increasing the number of embryos available for transfer."

Nonetheless, using CRISPR in that way remains a long way off.

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Shoukhrat Mitalipov, director of the Oregon Health & Science University's Center for Embryonic Cell and Gene Therapy, helped lead the new study. In 2013, Mitalipov and his colleagues reported the first success in cloning human stem cells , reprogramming human skin cells back to their embryonic state. In 2007, a research team led by Mitalipov announced that they created the first cloned monkey embryo and extracted stem cells from it.

Now, when it comes to using CRISPR to correct gene mutations in embryos, Mitalipov said Tuesday, "We've done some ground work. ... There is still a long road ahead, and it's unclear at this point when we will be allowed to move on."</s>Image copyright OHSU Image caption Pictures of the genetically modified embryos

Scientists have, for the first time, successfully freed embryos of a piece of faulty DNA that causes deadly heart disease to run in families.

It potentially opens the door to preventing 10,000 disorders that are passed down the generations.

The US and South Korean team allowed the embryos to develop for five days before stopping the experiment.

The study hints at the future of medicine, but also provokes deep questions about what is morally right.

Science is going through a golden age in editing DNA thanks to a new technology called Crispr, named breakthrough of the year in just 2015.

Its applications in medicine are vast and include the idea of wiping out genetic faults that cause diseases from cystic fibrosis to breast cancer.

Heart stopper

US teams at Oregon Health and Science University and the Salk Institute along with the Institute for Basic Science in South Korea focused on hypertrophic cardiomyopathy.

The disorder is common, affecting one in every 500 people, and can lead to the heart suddenly stopping beating.

It is caused by an error in a single gene (an instruction in the DNA), and anyone carrying it has a 50-50 chance of passing it on to their children.

In the study, described in the journal Nature, the genetic repair happened during conception.

Sperm from a man with hypertrophic cardiomyopathy was injected into healthy donated eggs alongside Crispr technology to correct the defect.

It did not work all the time, but 72% of embryos were free from disease-causing mutations.

Eternal benefit

Dr Shoukhrat Mitalipov, a key figure in the research team, said: "Every generation on would carry this repair because we've removed the disease-causing gene variant from that family's lineage.

"By using this technique, it's possible to reduce the burden of this heritable disease on the family and eventually the human population."

There have been multiple attempts before, including, in 2015, teams in China using Crispr-technology to correct defects that lead to blood disorders.

But they could not correct every cell, so the embryo was a "mosaic" of healthy and diseased cells.

Their approach also led to other parts of the genetic code becoming mutated.

Those technical obstacles have been overcome in the latest research.

However, this is not about to become routine practice.

The biggest question is one of safety, and that can be answered only by far more extensive research.

There are also questions about when it would be worth doing - embryos can already be screened for disease through pre-implantation genetic diagnosis.

However, there are about 10,000 genetic disorders that are caused by a single mutation and could, in theory, be repaired with the same technology.

Prof Robin Lovell-Badge, from the Francis Crick Institute, told the BBC: "A method of being able to avoid having affected children passing on the affected gene could be really very important for those families.

"In terms of when, definitely not yet. It's going to be quite a while before we know that it's going to be safe."

Nicole Mowbray lives with hypertrophic cardiomyopathy and has a defibrillator implanted in her chest in case her heart stops.

But she is unsure whether she would ever consider gene editing: "I wouldn't want to pass on something that caused my child to have a limited or painful life.

"That does come to the front of my mind when I think about having children.

"But I wouldn't want to create the 'perfect' child, I feel like my condition makes me, me."

Ethical?

Darren Griffin, a professor of genetics at the University of Kent, said: "Perhaps the biggest question, and probably the one that will be debated the most, is whether we should be physically altering the genes of an IVF embryo at all.

"This is not a straightforward question... equally, the debate on how morally acceptable it is not to act when we have the technology to prevent these life-threatening diseases must also come into play."

The study has already been condemned by Dr David King, from the campaign group Human Genetics Alert, which described the research as "irresponsible" and a "race for first genetically modified baby".

Dr Yalda Jamshidi, a reader in genomic medicine at St George's University of London, said: "The study is the first to show successful and efficient correction of a disease-causing mutation in early stage human embryos with gene editing.

"Whilst we are just beginning to understand the complexity of genetic disease, gene-editing will likely become acceptable when its potential benefits, both to individuals and to the broader society, exceeds its risks."

The method does not currently fuel concerns about the extreme end of "designer babies" engineered to have new advantageous traits.

The way Crispr is designed should lead to a new piece of engineered DNA being inserted into the genetic code.

However, in a complete surprise to the researchers, this did not happen.

Instead, Crispr damaged the mutated gene in the father's sperm, leading to a healthy version being copied over from the mother's egg.

This means the technology, for now, works only when there is a healthy version from one of the parents.

Prof Lovell-Badge added: "The possibility of producing designer babies, which is unjustified in any case, is now even further away."

Follow James on Twitter.</s>Society for Science & the Public, which publishes Science News, uses cookies to personalize your experience and improve our services. For more information on how we use cookies on our websites, visit our Cookie Policy</s>Scientists have been tinkering with the DNA in humans and other living things for decades. But one thing has long been considered off-limits: modifying human DNA in any way that could be passed down for generations.

Now, an international team of scientists reports they have, for the first time, figured out a way to successfully edit the DNA in human embryos — without introducing the harmful mutations that were a problem in previous attempts elsewhere. The work was published online Wednesday in the journal Nature.

"It's a pretty exciting piece of science," says George Daley, dean of the Harvard Medical School, who was not involved in the research. "It's a technical tour de force. It's really remarkable."

The research is ultimately aimed at helping families plagued by genetic diseases. The new experiment used a powerful new gene-editing technique to correct a genetic defect behind a heart disorder that can cause seemingly healthy young people to suddenly die from heart failure.

The experiment corrected the defect in nearly two-thirds of several dozen embryos, without causing potentially dangerous mutations elsewhere in the DNA.

None of the embryos were used to try to create a baby. But if future experiments confirm the techniques are safe and effective, the scientists say the same approach could be used to prevent a long list of inheritable diseases.

"Potentially, we're talking about thousands of genes and thousands of patients," says Paula Amato, an associate professor of obstetrics and gynecology at Oregon Health & Science University in Portland. She was a member of the scientific team from the U.S., China and South Korea.

Other diseases that might ultimately benefit from such an approach include Huntington's disease, cystic fibrosis, perhaps an inherited form of Alzheimer's disease and cases of breast and ovarian cancer caused by mutations in the BRCA genes.

Nonetheless, the work is setting off alarm bells among critics around the world.

"I think it's extraordinarily disturbing," says Marcy Darnovsky, who directs the Center for Genetics and Society, a genetics watchdog group in Berkeley, Calif. "It's a flagrant disregard of calls for a broad societal consensus in decisions about a really momentous technology that could be used good, but in this case is being used in preparation for an extraordinarily risky application."

"If irresponsible scientists are not stopped, the world may soon be presented with a fait accompli of the first [genetically modified] baby," says David King, who heads the U.K-based group Human Genetics Alert. "We call on governments and international organizations to wake up and pass an immediate global ban on creating cloned or GM babies, before it is too late."

Amato and others stress that their work is aimed at preventing terrible diseases, not creating genetically enhanced people. And they note that much more research is needed to confirm the technique is safe and effective before anyone tries to make a baby this way.

But scientists hoping to continue the work in the U.S. face many regulatory obstacles. The National Institutes of Health will not fund any research involving human embryos (the new work was funded by Oregon Health & Science University). And the Food and Drug Administration is prohibited by Congress from considering any experiments that involve genetically modified human embryos.

Nevertheless, the researchers say they're hopeful about continuing the work, perhaps in Britain. The United Kingdom has permitted genetic experiments involving human embryos forbidden in the United States.

"If other countries would be interested, we would be happy to work with their regulatory bodies," says Shoukhrat Mitalipov, director of the Oregon Health & Science University's Center for Embryonic Cell and Gene Therapy.

One major concern is safety to a developing embryo — whether genetically modified human embryos would indeed produce healthy babies. But on a broader level, any changes made in the DNA of an embryo would be passed down for generations. That raises fears that any mistakes in the editing that inadvertently caused new diseases could become a permanent part of that family's genetic blueprint.

Darnovsky and others also worry that modifying human DNA in an embryo could give rise to "designer babies." That's when parents pick and choose the traits of their children to try to make them smarter, taller, stronger or have other traits that make them seem superior. That's not yet technically possible. But critics fear scientists are already moving in that direction.

"The scenario is that you would have fertility clinics advertising to people who wanted to engineer their future children so that they could be presented as 'enhanced' — as biologically better than everyone else," Darnovsky says. "It's not a world we want to build. It's not a world we want to live in."

Unscrupulous researchers could also rush the technology into fertility clinics to try to start creating babies they can bill as genetically enhanced before the technology has even been proved safe, and before a societal consensus has been reached about what applications should be permitted.

"This is a strong statement that we can do genome editing," says Harvard's Daley. "The question that remains is: 'Should we?' We need a deeper public discourse around the ethical implications of this technology."

Darnovsky and some scientists argue that many couples who carry genetic diseases already have safer alternatives to this sort of gene editing. Couples carrying genetic diseases can go through in vitro fertilization (IVF) and have their embryos tested before being implanted in the womb.

"I will admit to experiencing a sense of puzzlement," says Fyodor Urnov, an associate director at the Altius Institute for Biomedical Sciences, a nonprofit research institute in Seattle.

"The question I have is: 'Why did you folks bother, given that there is a safe, effective, approved and ethical way to attain exactly the goal you have set out to do without any of the significant logical and ethic hurdles of having to edit a human embryo?" Urnov says.

Amato and the other scientists on the international team say their approach could offer an alternative for couples for whom those standard options won't work or are less desirable. But they agree the work should only move forward with careful regulatory oversight to prevent abuse.

"Anytime there's a new technology there's a potential for misuse. We have to acknowledge that," Amato says. "Personally I don't feel that's a reason not to pursue the research if you think there's a potential benefit that outweighs that risk. And I think if you can prevent serious disease in future generations, that makes it worthwhile to pursue this."

The advance was first reported last week in Technology Review, a magazine published by the Massachusetts Institute of Technology. But the details were withheld and the researchers did not elaborate until the scientific paper had finished being vetted by other scientists for publication in Nature.

For their experiments, the scientists obtained sperm from a donor carrying a mutation for the heart disorder cardiomyopathy. They then used that sperm to fertilize dozens of eggs obtained from healthy women.

At the same time as fertilization, the researchers injected a powerful, microscopic gene-editing tool known as CRISPR-Cas9. The new technique makes it much easier than previous approaches to make very precise changes in DNA.

Several scientists likened the approach to doing surgery on fetuses when they are in the womb. But this takes that idea much further and involves repairing damaged DNA at a molecular level in the womb.

"This is nano-surgery," says George Church, a prominent Harvard geneticist who also was not involved in the research. "You're doing it with the finest possible scalpel."

The editing tool very accurately cut into a mutated gene known as MYBPC3, which causes cardiomyopathy. To the researchers' surprise, the cut triggered the embryos to repair the defective gene on their own. This is a process that had previously been unknown, the scientists say.

"The most exciting moment was when we realized the mechanism of repair," Amato says. "It was fixing itself."

The researchers then let the embryos develop for several days so they could analyze them to see how well the experiments worked. In one part of the experiments involving 58 embryos, the approach corrected the mutation in more than 70 percent of the embryos, the researchers reported.

"The gene defect was corrected with high efficiency," Amato says.

In addition, a detailed genetic analysis of the embryos concluded that the gene editing had not caused safety problems.

"I think this is a significant advance," Church says. "This is important."

In 2015, Chinese scientists reported trying to edit the DNA of embryos for the first time, also using CRISPR-Cas9. But that experiment involved embryos that could never develop normally. And while those researchers did succeed in editing the targeted defect, it also produced unintended defects elsewhere in the embryos' DNA.

The scientists who conducted the new experiments say they think they avoided those problems by injecting CRISPR at the same time the eggs were being fertilized by sperm.

"That was key," Mitalipov says.

Alta Charo, a bioethicist at the University of Wisconsin, dismissed concerns about the work leading to designer babies.

"This is not the dawn of the era of the designer baby," says Charo, who co-chaired a committee formed by the National Academies of Sciences and the National Academy of Medicine to determine whether such experiments should be permissible. The committee concluded earlier this year that gene editing of human embryos could be allowed in rare cases when no other options are available — but only to treat diseases.

"I do not think that the constant drumbeat about the fear of designer baby is warranted, Charo says. "What this is, is a possible step toward being able to edit the DNA in human embryos that's reliable and precise."

In the meantime, scientists in Britain have won approval to use CRISPR to edit the DNA in healthy human embryos to learn more about normal human development. A team in Sweden has started similar experiments.

"I think this needs to be tightly regulated," says Fredrik Lanner, a geneticist at the Karolinska Institute in Stockholm who is conducting those experiments. "This is very exciting. But it also could be a double-edged sword. So I think we really have to be extra cautious with this technology."</s>Scientists for the first time have successfully edited genes in human embryos to repair a common and serious disease-causing mutation, producing apparently healthy embryos, according to a study published on Wednesday.

The research marks a major milestone and, while a long way from clinical use, it raises the prospect that gene editing may one day protect babies from a variety of hereditary conditions.

But the achievement is also an example of human genetic engineering, once feared and unthinkable, and is sure to renew ethical concerns that some might try to design babies with certain traits, like greater intelligence or athleticism.

Scientists have long feared the unforeseen medical consequences of making inherited changes to human DNA. The cultural implications may be just as disturbing: Some experts have warned that unregulated genetic engineering may lead to a new form of eugenics, in which people with means pay to have children with enhanced traits even as those with disabilities are devalued.

The study, published in the journal Nature, comes just months after a national scientific committee recommended new guidelines for modifying embryos, easing blanket proscriptions but urging the technique be used only for dire medical problems.

“We’ve always said in the past gene editing shouldn’t be done, mostly because it couldn’t be done safely,” said Richard Hynes, a cancer researcher at the Massachusetts Institute of Technology who co-led the committee. “That’s still true, but now it looks like it’s going to be done safely soon,” he said, adding that the research is “a big breakthrough.”

“What our report said was, once the technical hurdles are cleared, then there will be societal issues that have to be considered and discussions that are going to have to happen. Now’s the time.”

Scientists at Oregon Health and Science University, with colleagues in California, China and South Korea, reported that they repaired dozens of embryos, fixing a mutation that causes a common heart condition that can lead to sudden death later in life.

If embryos with the repaired mutation were allowed to develop into babies, they would not only be disease-free but also would not transmit the disease to descendants.

The researchers averted two important safety problems: They produced embryos in which all cells — not just some — were mutation-free, and they avoided creating unwanted extra mutations.

“It feels a bit like a ‘one small step for (hu)mans, one giant leap for (hu)mankind’ moment,” Jennifer Doudna, a biochemist who helped discover the gene-editing method used, called CRISPR-Cas9, said in an email.

Gene Editing in Embryos

 Scientists tried two techniques to remove a dangerous mutation. In the first, genetic “scissors” were inserted into fertilized eggs. The mutation was repaired in some of the resulting embryos but not always in every cell. The second method worked better: By injecting the “scissors” along with the sperm into the egg, more embryos emerged with repaired genes in every cell.

FIRST TECHNIQUE

 When gene-editing components were introduced into a fertilized egg, some embryos contained a patchwork of repaired and unrepaired cells.

“I expect these results will be encouraging to those who hope to use human embryo editing for either research or eventual clinical purposes,” said Dr. Doudna, who was not involved in the study.

Much more research is needed before the method could be tested in clinical trials, currently impermissible under federal law. But if the technique is found to work safely with this and other mutations, it might help some couples who could not otherwise have healthy children.

Potentially, it could apply to any of more than 10,000 conditions caused by specific inherited mutations. Researchers and experts said those might include breast and ovarian cancer linked to BRCA mutations, as well as diseases like Huntington’s, Tay-Sachs, beta thalassemia, and even sickle cell anemia, cystic fibrosis or some cases of early-onset Alzheimer’s.

“You could certainly help families who have been blighted by a horrible genetic disease,” said Robin Lovell-Badge, a professor of genetics and embryology at the Francis Crick Institute in London, who was not involved in the study.

“You could quite imagine that in the future the demand would increase. Maybe it will still be small, but for those individuals it will be very important.”

The researchers also discovered something unexpected: a previously unknown way that embryos repair themselves.

In other cells in the body, the editing process is carried out by genes that copy a DNA template introduced by scientists. In these embryos, the sperm cell’s mutant gene ignored that template and instead copied the healthy DNA sequence from the egg cell.

“We were so surprised that we just couldn’t get this template that we made to be used,” said Shoukhrat Mitalipov, director of the Center for Embryonic Cell and Gene Therapy at Oregon Health and Science University and senior author of the study. “It was very new and unusual.”

The research significantly improves upon previous efforts. In three sets of experiments in China since 2015, researchers seldom managed to get the intended change into embryonic genes.

And some embryos had cells that did not get repaired — a phenomenon called mosaicism that could result in the mutation being passed on — as well as unplanned mutations that could cause other health problems.

In February, a National Academy of Sciences, Engineering and Medicine committee endorsed modifying embryos, but only to correct mutations that cause “a serious disease or condition” and when no “reasonable alternatives” exist.

 Sheldon Krimsky, a bioethicist at Tufts University, said the main uncertainty about the new technique was whether “reasonable alternatives” to gene editing already exist.

As the authors themselves noted, many couples use pre-implantation genetic diagnosis to screen embryos at fertility clinics, allowing only healthy ones to be implanted. For these parents, gene editing could help by repairing mutant embryos so that more disease-free embryos would be available for implantation.

Hank Greely, director of the Center for Law and the Biosciences at Stanford, said creating fewer defective embryos also would reduce the number discarded by fertility clinics, which some people oppose.

 The larger issue is so-called germline engineering, which refers to changes made to embryo that are inheritable.

“If you’re in one camp, it’s a horror to be avoided, and if you’re in the other camp, it’s desirable,” Dr. Greely said. “That’s going to continue to be the fight, whether it’s a feature or a bug.”

For now, the fight is theoretical. Congress has barred the Food and Drug Administration from considering clinical trials involving germline engineering. And the National Institutes of Health is prohibited from funding gene-editing research in human embryos. (The new study was funded by Oregon Health and Science University, the Institute for Basic Science in South Korea, and several foundations.)

The authors say they hope that once the method is optimized and studied with other mutations, officials in the United States or another country will allow regulated clinical trials.

“I think it could be widely used, if it’s proven safe,” said Dr. Paula Amato, a co-author of the study and reproductive endocrinologist at O.H.S.U. Besides creating more healthy embryos for in vitro fertilization, she said, it could be used when screening embryos is not an option or to reduce arduous IVF cycles for women.

Dr. Mitalipov has pushed the scientific envelope before, generating ethical controversy with a so-called three-parent baby procedure that would place the nucleus of the egg of a woman with defective cellular mitochondria into the egg from a healthy woman. The F.D.A. has not approved trials of the method, but Britain may begin one soon.

The new study involves hypertrophic cardiomyopathy, a disease affecting about one in 500 people, which can cause sudden heart failure, often in young athletes.

It is caused by a mutation in a gene called MYBPC3. If one parent has a mutated copy, there is a 50 percent chance of passing the disease to children.

 Using sperm from a man with hypertrophic cardiomyopathy and eggs from 12 healthy women, the researchers created fertilized eggs. Injecting CRISPR-Cas9, which works as a genetic scissors, they snipped out the mutated DNA sequence on the male MYBPC3 gene.

They injected a synthetic healthy DNA sequence into the fertilized egg, expecting that the male genome would copy that sequence into the cut portion. That is how this gene-editing process works in other cells in the body, and in mouse embryos, Dr. Mitalipov said.

Instead, the male gene copied the healthy sequence from the female gene. The authors don’t know why it happened.

Maybe human sex cells or gametes evolved to repair themselves because they are the only cells that transmit genes to offspring and “need special protection,” said Juan Carlos Izpisua Belmonte, a co-author and geneticist at the Salk Institute.

Out of 54 embryos, 36 emerged mutation-free, a significant improvement over natural circumstances in which about half would not have the mutation. Another 13 embryos also emerged without the mutation, but not in every cell.

The researchers tried to eliminate the problem by acting at an earlier stage, injecting the egg with the sperm and CRISPR-Cas9 simultaneously, instead of waiting to inject CRISPR-Cas9 into the already fertilized egg.

That resulted in 42 of 58 embryos, 72 percent, with two mutation-free copies of the gene in every cell. They also found no unwanted mutations in the embryos, which were destroyed after about three days.

The method was not perfect. The remaining 16 embryos had unwanted additions or deletions of DNA. Dr. Mitalipov said he believed fine-tuning the process would make at least 90 percent of embryos mutation-free.

And for disease-causing mutations on maternal genes, the same process should occur, with the father’s healthy genetic sequence being copied, he said.

But the technique will not work if both parents have two defective copies. Then, scientists would have to determine how to coax one gene to copy a synthetic DNA sequence, Dr. Mitalipov said.

Otherwise, he said, it should work with many diseases, “a variety of different heritable mutations.”

 R. Alta Charo, a bioethicist at University of Wisconsin at Madison, who led the committee with Dr. Hynes, said the new discovery could also yield more information about causes of infertility and miscarriages.

She doubts a flood of couples will have “edited children.”

“Nobody’s going to do this for trivial reasons,” Dr. Charo said. “Sex is cheaper and it’s more fun than IVF, so unless you’ve got a real need, you’re not going to use it.”</s>In the landmark trials, the US and South Korean team demonstrated how they can use CRISPR technology (a revolutionary tool used to edit DNA) to successfully free the embryo from a faulty piece of DNA introduced by one of the parents at conception.

This opens the door to potentially tackle thousands of inherited diseases, but this study focused specifically on hypertrophic cardiomyopathy, a condition that causes the heart’s muscular wall to thicken and affects one in every 500 people worldwide.

Caused by an error in a single gene, anyone carrying it has a 50% chance of passing it on to their future children, but editing the DNA removes this risk.

Dr Shoukhrat Mitalipov, who worked on the study, wrote in the ‘Nature’ journal: “Every generation on would carry this repair because we’ve removed the disease-causing gene variant from that family’s lineage.

“By using this technique, it’s possible to reduce the burden of this heritable disease on the family and eventually the human population.”

Taking sperm from a male donor who has hypertrophic cardiomyopathy, and an egg from a healthy woman, the team injected the CRISPR technology at the point of fertilisation to carry out the genetic repairs.

Although it was not 100% successful, the attempt worked in 72% of the 58 embryos - the biggest success rate anywhere in the world so far.

The embryos were then allowed to develop for five days, before the experiment was stopped; as no work of this kind with modified embryos is actually permitted to carry children to term, it is only for purposes of “better understanding” human development.

This includes in the UK where, according to the UK Human Fertilisation and Embryology Authority (HFEA) 2016 licensing, embryos must be destroyed within 14 days and cannot be implanted into a woman after being altered.

A spokesperson for HFEA said: “UK researchers can apply for a license to edit human embryos in research, but offering it as a treatment is currently illegal.”

This is the first time such a trial has taken place outside of China, where laws are more relaxed.

But all previous Chinese trials (the most recent was in 2015) have not been this successful, and have resulted in “mosaic” cells that are a tapestry of healthy and unhealthy cells, as well as parts of the genetic code being mutated.

More work is needed to prove that gene editing would be safe to do in people, but even if it seems safe, scientists face major regulatory hurdles before clinical trials could start.

Today, people who carry certain genetic diseases can opt for IVF and have their embryos screened for harmful mutations but there are many ethical questions about the potential for creating “designer” babies that could be “edited” to have a specific intelligence, height, facial appearance or hair colour.</s>WASHINGTON — Altering human heredity? In a first, researchers safely repaired a disease-causing gene in human embryos, targeting a heart defect best known for killing young athletes — a big step toward one day preventing a list of inherited diseases.

In a surprising discovery, a research team led by Oregon Health and & Science University reported Wednesday that embryos can help fix themselves if scientists jump-start the process early enough.

It’s laboratory research only, nowhere near ready to be tried in a pregnancy. But it suggests that scientists might alter DNA in a way that protects not just one baby from a disease that runs in the family, but his or her offspring as well. And that raises ethical questions.

“I for one believe, and this paper supports the view, that ultimately gene editing of human embryos can be made safe. Then the question truly becomes, if we can do it, should we do it?” said Dr. George Daley, a stem cell scientist and dean of Harvard Medical School. He wasn’t involved in the new research and praised it as “quite remarkable.”

“This is definitely a leap forward,” agreed developmental geneticist Robin Lovell-Badge of Britain’s Francis Crick Institute.

Today, couples seeking to avoid passing on a bad gene sometimes have embryos created in fertility clinics so they can discard those that inherit the disease and attempt pregnancy only with healthy ones, if there are any.

Gene editing in theory could rescue diseased embryos. But so-called “germline” changes — altering sperm, eggs or embryos — are controversial because they would be permanent, passed down to future generations. Critics worry about attempts at “designer babies” instead of just preventing disease, and a few previous attempts at learning to edit embryos, in China, didn’t work well and, more importantly, raised safety concerns.

In a series of laboratory experiments reported in the journal Nature, the Oregon researchers tried a different approach.

They targeted a gene mutation that causes a heart-weakening disease, hypertrophic cardiomyopathy, that affects about 1 in 500 people. Inheriting just one copy of the bad gene can cause it.

The team programmed a gene-editing tool, named CRISPR-Cas9, that acts like a pair of molecular scissors to find that mutation — a missing piece of genetic material.

Then came the test. Researchers injected sperm from a patient with the heart condition along with those molecular scissors into healthy donated eggs at the same time. The scissors cut the defective DNA in the sperm.

Normally cells will repair a CRISPR-induced cut in DNA by essentially gluing the ends back together. Or scientists can try delivering the missing DNA in a repair package, like a computer’s cut-and-paste program.

Instead, the newly forming embryos made their own perfect fix without that outside help, reported Oregon Health & Science University senior researcher Shoukhrat Mitalipov.

We all inherit two copies of each gene, one from dad and one from mom — and those embryos just copied the healthy one from the donated egg.

“The embryos are really looking for the blueprint,” Mitalipov, who directs OHSU’s Center for Embryonic Cell and Gene Therapy, said in an interview. “We’re finding embryos will repair themselves if you have another healthy copy.”

It worked 72 per cent of the time, in 42 out of 58 embryos. Normally a sick parent has a 50-50 chance of passing on the mutation.

Previous embryo-editing attempts in China found not every cell was repaired, a safety concern called mosaicism. Beginning the process before fertilization avoided that problem: Until now, “everybody was injecting too late,” Mitalipov said.

Nor did intense testing uncover any “off-target” errors, cuts to DNA in the wrong places, reported the team, which also included researchers from the Salk Institute for Biological Studies in California and South Korea’s Institute for Basic Science. None of the embryos was allowed to develop beyond eight cells, a standard for laboratory research.

Genetics and ethics experts not involved in the work say it’s a critical first step — but just one step — toward eventually testing the process in pregnancy, something currently prohibited by U.S. policy.

“This is very elegant lab work,” but it’s moving so fast that society needs to catch up and debate how far it should go, said Johns Hopkins University bioethicist Jeffrey Kahn.

And lots more research is needed to tell if it’s really safe, added Britain’s Lovell-Badge.

“What we do not want is for rogue clinicians to start offering treatments” that are unproven like has happened with some other experimental technologies, he stressed.

Among key questions: Would the technique work if mom, not dad, harboured the mutation? Is repair even possible if both parents pass on a bad gene?

Mitalipov is “pushing a frontier,” but it’s responsible basic research that’s critical for understanding embryos and disease inheritance, noted University of Pittsburgh professor Kyle Orwig.

In fact, Mitalipov said the research should offer critics some reassurance: If embryos prefer self-repair, it would be extremely hard to add traits for “designer babies” rather than just eliminate disease.

“All we did is un-modify the already mutated gene.”

This Associated Press series was produced in partnership with the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

This story is part of Genetic Frontiers, AP’s ongoing exploration of the rapidly growing understanding of DNA and new attempts to manipulate it.</s>Scientists have successfully used CRISPR , a tool that cuts DNA with more precision than any other genome editing technology, to fix a genetic defect in human embryos that can cause serious heart problems, according to a landmark new study in the journal Nature. This is the first use of CRISPR on human embryos in the U.S.

Chinese scientists have reported using CRISPR to correct genetic defects in human embryos, but some of the embryos they used weren’t viable.

Shoukhrat Mitalipov, from Oregon Health & Science University, collaborated with researchers at the Salk Institute, as well as with scientists from China and South Korea, to improve on those results. They applied CRISPR at the earliest stage possible—when the embryo is still a single cell—to ensure that the genetic changes they introduced were propagated to every cell of the embryo as it divided and developed. Because the embryos were created for research purposes only, none were allowed to develop beyond three days.

MORE: First CRISPR Human Trial Approved in the U.S.

CRISPR, which was introduced in 2012, precisely cuts DNA but does not repair it. If combined with other techniques, however, researchers say it could both cut out disease-causing genes and replace them with healthy versions to essentially cure genetic human diseases. So in order to further the science, Mitalipov and his colleagues wanted to test what happened when CRISPR was used in a human embryo. Theoretically, once CRISPR broke the DNA in the appropriate place to cut out a mutation, the cell’s natural repair mechanisms would kick in to repair the injury, fixing the defect this time with the proper code—much like how a word processor's autocorrect function fixes spelling mistakes.

Unfortunately, this process isn’t very efficient in adult cells in which CRISPR has been tested, so Mitalipov expected similarly low yields in the embryos.

To his surprise, however, he found that embryos were very effective at fixing breaks in DNA.

He created embryos that contained a specific defect known to cause a heart condition by fertilizing healthy donor eggs from various women with sperm from a man who carried the genetic mutation for the disease. He then introduced CRISPR to splice out the mutated gene in more than 50 embryos just after the sperm fertilized the eggs, when the embryos were still just one cell. Several days later, 72% of the embryos showed no sign of the mutated gene; the gene was essentially corrected in all of their cells.

MORE: How the Science of CRISPR Can Change Your Genes

It turns out that the embryo relies on the normal copy of the gene, in this case from the egg, to fix the break made when CRISPR cut out the mutated gene. They key was to introduce CRISPR early enough so the embryo’s own DNA repair system could fix the mutated gene. That’s encouraging for one potential use of CRISPR in the future as a way to correct inherited genetic disease, says Mitalipov, since the embryo seems to have a built-in, reliable way of repairing the injury caused by splicing out an abnormal gene.

“Genetic diseases that are heritable can be treated this way as early as possible,” he says. “It’s the best way to treat the disease before the genetic mutation is actually transmitted to the embryo.”

MORE: New Technique That Lets Scientists Edit DNA Is Transforming Science—and Raising Difficult Questions

Currently, the most reliable way of screening for such inherited defects is by using IVF, screening the resulting embryos for the mutation and transferring only those without the mutation for pregnancy. But that may require several cycles of IVF, which is expensive and carries with it side effects and complications, before enough genetically healthy embryos are created.

The study results don’t mean that editing human embryos to correct genetic diseases will be available at hospitals anytime soon. While that’s the goal, the findings are just the first in a series of studies that will need to be done to document the safety and reliability of using CRISPR to fix human disease. For one, the efficiency of the CRISPR and repair process is still about 70%. “There is still work to do to improve the efficiency,” says Mitalopov. “But I think that’s possible to do.”

MORE: HIV Genes Have Been Cut Out of Live Animals Using CRISPR

He’s also encouraged by the fact that the gene editing and repair did not introduce other errors in the DNA. While it’s the most accurate DNA editor available, one of CRISPR's drawbacks is that it can cut the genome in unintended places, especially where letters in the code look very similar to the target (again, similar to the way autocorrect can sometimes introduce more errors in attempting to fix a misspelling). Mitalipov’s team found no such off-target effects, a sign that CRISPR editing, at least in this study, was relatively safe. He notes, however, that may simply be an artifact of the particular gene he targeted; there may be coincidentally no parts of the genome that have similar sequences as the gene that CRISPR cut.

Even beyond the medical questions, there are also ethical concerns about the power inherent in manipulating the human genome. While correcting devastating diseases such as the heart condition Mitalipov studied, which can cause sudden death in young people, isn’t ethically controversial, using CRISPR to modify other genes—for intelligence, say, or athleticism or physical attributes like eye color or height—is much more problematic. The concerns are especially acute when it comes to eggs, sperm and embryos, since changes in these can be passed down to the next generation and forever change the human gene pool. The embryos that Mitalipov created were never intended to be transferred for pregnancy. But had they been allowed to develop, they would not contain the heart disease mutation, and they would not pass on the mutation to their offspring. The CRISPR editing would essentially eliminate the mutation from that family’s pedigree. Editing changes in already developed cells in adults aren’t inherited, so are less worrisome in terms of their legacy.

MORE : Pandora’s Baby: How A New Type Of Prenatal Genetic Testing Could Predict Your Child

For now, there are legal and regulatory hurdles to moving the research closer to human trials. The National Institutes of Health (NIH) does not provide funding for using CRISPR in human embryo research. The Food and Drug Administration is banned from considering studies that involve genetic altering of human eggs, sperm or embryos. Mitalipov and his team used funding from Oregon Health & Science and did not rely on any NIH support.</s>Using a powerful gene-editing technique, scientists have rid human embryos of a mutation that causes an inherited form of heart disease often deadly to healthy young athletes and adults in their prime.

The experiment marks the first time that scientists have altered the human genome to ensure a disease-causing mutation would disappear not only from the DNA of the subject on which it’s performed, but from the genes of his or her progeny as well.

The controversial procedure, known as “germ-line editing,” was conducted at Oregon Health & Science University using human embryos expressly created for the purpose. It was reported Wednesday in the journal Nature.

The new research comes less than six months after the National Academies of Science, Engineering and Medicine recommended that scientists limit their trials of human germ-line editing to diseases that could not be treated with “reasonable alternatives” — at least for now.

In a bid to make the experiment relevant to real-life dilemmas faced by parents who carry genes for inherited diseases, the researchers focused their editing efforts on a mutation that causes inherited hypertrophic cardiomyopathy.

In this genetic condition, a parent who carries one normal and one faulty copy of a the MYBPC3 gene has a 50-50 chance of passing that mutation on to his or her offspring. If the child inherits the mutation, his or her heart muscle is likely to grow prematurely weak and stiff, causing heart failure and often early death.

In diseases where one parent carries such an “autosomal dominant” mutation, a couple will often seek the assistance of fertility doctors to minimize the risk of passing such a mutation on to a child. A woman’s egg production is medically stimulated, and eggs and sperm meet in a lab — a process called in vitro fertilization. Then embryologists inspect the resulting embryos, cull the ones that have inherited an unwanted mutation, and transfer only unaffected embryos into a woman’s uterus to be carried to term.

In the new research, researchers set out to test whether germ-line gene editing could make the process of choosing healthy embryos more effective and efficient by creating more of them.

In the end, their experiment showed it could. The targeted correction of a disease-causing gene carried by a single parent “can potentially rescue a substantial portion of mutant human embryos, thus increasing the number of embryos available for transfer,” the authors wrote in Nature. Co-author Dr. Paula Amato, an Oregon Health & Science University (OHSU) professor of obstetrics and gynecology, said the technique “could potentially decrease the number of cycles needed for people trying to have children free of genetic disease” if it’s found safe for use in fertility clinics.

Along the way, though, many of the researchers’ findings were scientifically surprising. Long-feared effects of germ-line editing, including collateral damage to “off-target” genetic sequences, scarcely materialized. And “mosaicism,” a phenomenon in which edited DNA appears in some but not all cells, was found to be minimal.

The study’s lead author, OHSU biologist Shoukhrat Mitalipov, called these “exciting and surprising moments.” But he cautioned that “there is room to improve” the techniques demonstrated to produce mutation-free embryos. As for conducting human clinical trials of the germ-line correction, he said those would have to wait until results showed a near-perfect level of efficiency and accuracy, and could be limited by state and federal regulations.

Eventually, Mitalipov said, such germ-line gene editing might also make it easier for parents who carry other gene mutations that follow a similar pattern of inheritance — including some that cause breast and ovarian cancers, cystic fibrosis and muscular dystrophy — to have healthy children who would not pass those genes to their own offspring.

“There is still a long road ahead,” predicted Mitalipov, who heads the Center for Embryonic Cell and Gene Therapy at the Portland university.

The research drew a mix of praise and concern from experts in genetic medicine.

Dr. Richard O. Hynes, who co-chaired the National Academies’ report issued in February, called the new study “very good science” that advances understanding of genetic repair on many fronts. Hynes, who was not involved with the latest research effort, said he was “pleasantly surprised” by researchers’ “clever modifications” and their outcomes.

“It’s likely to become feasible, technically — not tomorrow, not next year, but in some foreseeable time. Less than a decade, I’d say,” said Haynes, a biologist and cancer researcher at MIT and the Howard Hughes Medical Institute.

UC Berkeley molecular and cell biologist Jennifer Doudna, one of pioneers of the CRISPR-Cas9 gene-editing technique, acknowledged the new research highlights a prospective use of gene editing for one inherited disease and offers some insights into the process.

But Doudna questioned how broadly the experiment’s promising results would apply to other inherited diseases. She said she does not believe the use of germ-line editing as a means to improve efficiency at infertility clinics meets the criteria laid out by the National Academies of Science, which urged that the techniques only be explored as treatment for diseases with “no reasonable alternative.”

“Already, 50% of embryos would be normal,” said Doudna. “Why not just implant those?”

Doudna said she worried that the new findings “will encourage people to proceed down this road” before the scientific and ethical implications of germ-line editing have been fully considered.

“A large group of experts concluded that clinical use should not proceed until and unless there’s broad societal consensus, and that just hasn’t happened,” Doudna said. “This study underscores the urgency of having those debates. Because it’s coming.”

What is clear is that the researchers — a multinational team of geneticists, cardiologists, fertility experts and embryologists from OHSU and from labs in South Korea and China — tried a number of innovations in an effort to improve the safety, efficiency and fidelity of gene editing. And most yielded promising results.

After retrieving eggs from 12 healthy female volunteers, researchers simultaneously performed two steps that had never been combined in a lab: At the same moment that they fertilized the eggs with the sperm of a man who carried a single copy of the mutated gene, they introduced the CRISPR-Cas9 repair machinery.

The resulting embryos took up the genetic-editing program so efficiently and uniformly that, after five days of incubation, 72.4% of the embryos (42 of 58) created and tested were free of the MYBPC3 mutation. By comparison, when sperm carrying the single mutation was used to fertilize eggs without any genetic manipulation, just 47.4% of embryos were free of the mutation linked to the deadly heart condition.
Teams of United States-based researchers, composed of American, Chinese and South Korean scientists, successfully edit a piece of faulty DNA that causes a deadly form of heart disease from cells in human embryos.