Breakthrough: Human Embryos Successfully and Safely Gene-Edited

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The result was one-cell embryos, known as zygotes, with a defective gene responsible for the heart condition from the man along with a healthy copy of the gene from the woman. The researchers didn't notice any "off-target" effects on the DNA, either.

In this July 31, 2017 photo provided by Oregon Health & Science University, Shoukhrat Mitalipov, left, talks with research assistant Hayley Darby in the Mitalipov Lab at OHSU in Portland, Ore. In this case, the gene-edited embryos would grow up to be healthy people who don't pass along a disease gene to their children.

Prospective parents can already look for and eliminate known disease genes by going through in vitro fertilization and having the resulting embryos screened for the genes. Instead, embryos used the mother's healthy copy of the gene to fix the cut. She said that while pre-implantation genetic screening of embryos is now available, it isn't ideal.

Though the federal government essentially bars clinical trials involving genetically modified embryos, the National Academy of Sciences adopted principles earlier this year that would allow them if they are limited to preventing a serious disease, would only involve editing applicable genes and when there are no reasonable alternatives.

After CRISPR cut out those bad segments, the embryo itself repaired the cut. Sometimes eggs had already copied DNA, and a mutant gene escaped editing (top, middle). They effectively corrected the problematic sperm gene 72 per cent of the time, and even in those instances where they did not correct it, the problematic gene was still deleted. "Our expectation was that this was how embryos would respond". And how concerned should we be about the ethical implications of the technology?

Scientists in the U.S. reached a new milestone by successfully altering DNA in defective embryos so they were no longer programmed to develop heart failure.

"On the other hand, the trajectory is for this technology to be sufficiently robust that it will eventually be used", Kalichman wrote.

Mitalipov's team took several steps to improve the safety of the technique. But Mitalipov's technique would have to be tested in a clinical trial that is banned in the United States.

With advances in stem cell technologies and gene editing, researchers are finally starting to address disease-causing mutations that impact potentially millions of people. Mitalipov thinks it would work if the mutant gene is maternal, but the problem of getting enough donor oocytes will make this hard to verify.

OHSU said the study's research adhered to guidelines established by the university's Institutional Review Board and additional ad-hoc committees set up for scientific and ethical review. "It's unclear at this point when we would be able to move on".

Not everybody is in favour of gene editing being used to prevent heritable conditions in the future.

"We need more debate", Wu said. "The technique was used to make a correction using existing wild-type maternal genes". "But for now, scientists just need to do more basic research".

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.

"I think we are at a very pivotal moment with this study", said bioethicist Marcy Darnovsky of the Center for Genetics and Society, a past critic of engineering inherited genes. "The results reflect much-needed progress in utilizing human eggs and sperm in research for the prevention of diseases which have no current cure or treatment". "The consequences and the ethics of it, they're not addressing that in any honest or meaningful way", she says. It increased the number of repaired embryos from 50 percent, which would have occurred naturally, to 74 percent. In earlier research in China, the modified DNA was taken up by only some cells, not all, and suffered other setbacks, raising questions about its effectiveness.

The new study, published in Nature, is different because it deals with viable human embryos and shows that the genome editing can be carried out safely - without creating harmful mutations.

A group of South Korean and US scientists successfully corrected a disease-causing mutation in human embryos, a local research institute said Thursday, a groundbreaking discovery that would open up new pathways to treat and prevent genetic diseases.

Professor Peter Braude, from King's College London, said the work showed how rapidly the field of gene editing had progressed. Remarkably, no "off-target" effects were detected.

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