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> 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> Scientists have cured human embryos of a blood disorder in a first-ever technique that could one day stamp out inherited diseases.

Researchers with Sun Yat-sen University in China performed “chemical surgery” on the lab-made embryos to remove the disease called beta thalassemia, which reduces the production of hemoglobin, according to the BBC.

“We are the first to demonstrate the feasibility of curing genetic disease in human embryos by base editor system,” said researcher Junjiu Huang.

Huang said the study creates the possibility of treating patients and preventing babies being born with beta thalassemia — “and even other inherited diseases.”

The experiment was conducted on tissue taken from a patient with the blood disorder and human embryos made through cloning.

Researchers used a technique called “base editing,” which alters the fundamental building blocks of DNA — adenine, cytosine, guanine and thymine, commonly known by their respective first letters, A, C, G and T.

Beta thalassemia is caused by a fault called a point mutation — a change to a single base in the genetic code.

Researchers used base editing to change a G base to an A — successfully curing the DNA of the blood disorder.

Base editing is an advanced form of gene editing called Crispr, which breaks DNA.

David Liu, who pioneered the technique at Harvard University, said the method is preferred because it creates fewer side effects than Crispr.

“About two-thirds of known human genetic variants associated with disease are point mutations,” said Liu. “So base editing has the potential to directly correct, or reproduce for research purposes, many pathogenic [mutations].” </s> Chinese scientists have successfully altered the genetic code of a human embryo, an “ingenious” breakthrough that experts believe could be key to eradicating hereditary diseases.

Using a technique known as ‘base editing’, researchers from Sun Yat-sen University in Guangzhou filtered through three-billion ‘letters’ of our genetic code to remove a single error responsible for a potentially deadly blood disorder.

"We are the first to demonstrate the feasibility of curing genetic disease in human embryos by base editor system,”Junjiu Huang, one of the scientists involved in the research, told BBC.

During the experiments, which were carried out on tissues taken from a patient with the blood disorder beta-thalassemia and inserted into cloned human embryos, a strand of DNA was examined to pinpoint the offending base. The team then used base editing, a more advanced form of the Crispr gene-editing technique to repair the faulty gene.

Such is the level of precision involved in base editing that Professor David Liu of Harvard University, a pioneer of the technique, dubbed it “chemical surgery.”

“Base editing has the potential to directly correct, or reproduce for research purposes, many pathogenic [mutations]," Liu said, adding that it is more efficient than Crispr as it has fewer unexpected side-effects.

The study, which has been published in the journal Protein and Cell, presents serious ethical questions for scientists.

While describing parts of the study as “ingenious,” Professor Robin Lovell-Badge of the Crick Institute in London called for robust regulation the techniques employed in gene editing.

"There would need to be far more debate, covering the ethics, and how these approaches should be regulated,” Lovell-Badge said. "And in many countries, including China, there needs to be more robust mechanisms established for regulation, oversight, and long-term follow-up."

The debate is also raging in the US, where the National Academy of Science and the National Academy of Medicine recommended easing the blanket ban on modifying DNA in February this year.

“We’ve always said in the past gene editing shouldn’t be done, mostly because it couldn’t be done safely. That’s still true, but now it looks like it’s going to be done safely soon,” Richard Hynes, a cancer researcher at the Massachusetts Institute of Technology who co-led the committee, told the New York Times. </s> Chinese scientists used an adapted version of a controversial gene-editing technique to correct a disease-causing mutation in human embryos, a medical first cautiously hailed by other experts Thursday.

The team used a so-called "base editor" -- an adaptation of the CRISPR-Cas9 DNA snipping tool -- to correct a single, mutated "letter" among about three billion in the intricate coding of the human genome.

The targeted mutation can cause humans to be born with beta-Thalassaemia, a potentially fatal genetic blood disorder.

"This study demonstrated the feasibility of curing genetic diseases in human... embryos by base editor system," the team wrote in the specialist journal Protein & Cell.

The journal sparked controversy when it published a paper in 2015 in which the same authors reported on experiments with CRISPR-Cas9 to modify the thalassaemia gene.

That paper led to calls for a halt to experiments involving the genetic editing of human embryos.

Many fear such technology could lead to so-called "designer babies" with desired features such as intelligence engineered into their genes.

For the new study, Puping Liang of the Sun Yat-sen University in China, and a team used a technique based on CRISPR-Cas9, which allows scientists to remove and replace a faulty strand of DNA with pinpoint precision.

Instead of using the Cas9 protein as "scissors" to eliminate the mutated "letter", they used an enzyme to change it.

- Can it be improved? -

DNA is the instruction booklet for cells to make and sustain life.

It resembles a zipper-like spiral -- the teeth on each strand are "base pairs" of encoding "letters" that chemically match with each other.

Adenine teams up with thymine to create the A-T base pair, while cytosine pairs with guanine for the C-G pair.

Thalassaemia can be caused by an "A" base letter converted to a "G" in a specific location of the gene.

For the latest study, the team sought to chemically change the "C" partner of the mutant "G", to a "T".

This would cause the errant "G" to automatically convert to an "A", expert Robin Lovell-Badge of the Francis Crick Institute, who was not involved in the study, explained via the Science Media Centre.

The method eliminated the need to cut DNA, and the team were successful about one in five times.

They worked with cloned embryos that were kept alive for just a few days for the purposes of lab experimentation

Observers said the technique appeared to be an improvement on standard CRISPR-Cas9.

"This powerful study sheds new light on precise gene correction for single gene disorders," commented Helen Claire O'Neill of University College London.

"It remains to be seen whether the efficiency... can be improved upon."

For Darren Griffin, a genetics professor at the University of Kent, the paper showed that "the ethical implications of gene manipulation in embryos need a thorough examination where safety is of paramount concern."

US-based scientists in August reported using CRISPR-Cas9 to repair a disease-causing mutation in the DNA of early-stage human embryos.

Last week, British scientists said they had used CRISPR-Cas9 to reveal the role of a key gene in the early development of human embryos. </s> Image copyright Getty Images

Precise "chemical surgery" has been performed on human embryos to remove disease in a world first, Chinese researchers have told the BBC.

The team at Sun Yat-sen University used a technique called base editing to correct a single typo out of the three billion "letters" of our genetic code.

They altered lab-made embryos to remove the disease beta-thalassemia. The embryos were not implanted.

The team says the approach may one day treat a range of inherited diseases.

Base editing alters the fundamental building blocks of DNA: the four bases adenine, cytosine, guanine and thymine.

They are commonly known by their respective letters, A, C, G and T.

All the instructions for building and running the human body are encoded in combinations of those four bases.

Image copyright Getty Images

The potentially life-threatening blood disorder beta-thalassemia is caused by a change to a single base in the genetic code - known as a point mutation.

The team in China edited it back.

They scanned DNA for the error then converted a G to an A, correcting the fault.

Junjiu Huang, one of the researchers, told the BBC News website: "We are the first to demonstrate the feasibility of curing genetic disease in human embryos by base editor system."

He said their study opens new avenues for treating patients and preventing babies being born with beta-thalassemia, "and even other inherited diseases".

The experiments were performed in tissues taken from a patient with the blood disorder and in human embryos made through cloning.

Genetics revolution

Base editing is an advance on a form of gene-editing known as Crispr, that is already revolutionising science.

Crispr breaks DNA. When the body tries to repair the break, it deactivates a set of instructions called a gene. It is also an opportunity to insert new genetic information.

Base editing works on the DNA bases themselves to convert one into another.

Prof David Liu, who pioneered base editing at Harvard University, describes the approach as "chemical surgery".

He says the technique is more efficient and has fewer unwanted side-effects than Crispr.

He told the BBC: "About two-thirds of known human genetic variants associated with disease are point mutations.

"So base editing has the potential to directly correct, or reproduce for research purposes, many pathogenic [mutations]."

Image copyright Getty Images

The research group at Sun Yat-sen University in Guangzhou hit the headlines before when they were the first to use Crispr on human embryos.

Prof Robin Lovell-Badge, from the Francis Crick Institute in London, described parts of their latest study as "ingenious".

But he also questioned why they did not do more animal research before jumping to human embryos and said the rules on embryo research in other countries would have been "more exacting".

The study, published in Protein and Cell, is the latest example of the rapidly growing ability of scientists to manipulate human DNA.

It is provoking deep ethical and societal debate about what is and is not acceptable in efforts to prevent disease.

Prof Lovell-Badge said these approaches are unlikely to be used clinically anytime soon.

"There would need to be far more debate, covering the ethics, and how these approaches should be regulated.

"And in many countries, including China, there needs to be more robust mechanisms established for regulation, oversight, and long-term follow-up."

Follow James on Twitter. </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> 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> In the wake of the first gene-edited embryos in the US being created earlier this year, Chinese researchers have employed a different technique to swap a single base in a human embryo's genome.

The precise edit was designed to return functionality to a gene responsible for a component of haemoglobin, which in its mutated form results in an often fatal blood condition called beta-thalassaemia.

A team of researchers from Sun Yat-sen University in Guangzhou, China, used what's called a base editor technique to change a single G back to an A in the DNA code of an embryonic cell's HBB gene.

The change might have been tiny, but in its mutated form HBB can't produce the protein beta-globin needed to build the oxygen-carrying haemoglobin for our red blood cells.

A shortage of haemoglobin means a shortage of oxygen, impeding growth and development and leading to a lifetime of blood transfusions to treat anaemia – if the embryo survives at all.

Beta-thalassaemia is usually a recessive condition, meaning both parents need to contribute a copy of the mutated gene for anaemia to develop in their child.

Correcting the mutations in this gene could help parents carry an embryo to term, or remove the trait from family lines.

About 400 different kinds of code-corruptions can affect HBB.

In this case, the researchers focussed on a single point-mutation that targets a base called cytosine (C) and exchanges it for one called thymine (T).

Each of these letters complements the other two kinds of base – thymine is a jigsaw-puzzle piece that matches adenine (A), while cytosine matches guanine (G).

By swapping a C for a T, the mutation should revert back to the proper 'A' code.

If this base editing technology seems unnecessarily complicated, there's a good reason for doing a genetic do-si-do – it means the strand of DNA isn't being snipped all the way through.

To test if the procedure was feasible, the team created a cell line with pieces of the gene embedded inside and then used two different base editing techniques to change the code.

Satisfied the editing could be done, they took the process to the next level and edited the gene in skin cells from a beta-thalassemia patient.

Researchers transferred the nucleus of the patient's skin cells into 30 mature oocytes – or human egg cells.

One of the techniques was then applied to the 26 cells that survived the cloning procedure, which successfully turned the G to an A in 9 of the embryos, and a G to a C (cytosine) in one.

None of the embryos were developed further or implanted.

Gene editing has been big news in recent years with advances in the application of a technology called CRISPR, which uses enzymes found in bacteria to chew up DNA at a specific location.

Applying this kind of corrective genetic surgery to human embryos could spell an end to a variety of inherited conditions, but so far efforts have been controversial, to say the least.

Questions have developed recently on whether or not the technology produces unwanted mutations, indicating that for all of its promise, it's still early days for this revolutionary engineering tool.

Base editing won't replace CRISPR, but could be a more delicate solution for those solitary mutations.

"We are the first to demonstrate the feasibility of curing genetic disease in human embryos by base editor system," researcher Junjiu Huang told the BBC.

Feasibility is the word here. We're nowhere near a safe operating procedure for repairing genes we consider broken in embryos.

But each careful step, coupled with healthy public debate, brings us a bit closer to an age when debilitating conditions like beta-thalassemia will be notes in a medical history book.

This research was published in Protein & Cell.
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.