U.S. scientists have succeeded in alteringthe genes of a human embryo to correct a disease-causingmutation, making it possible to prevent the defect from beingpassed on to future generations.The milestone, published this week in the journal Nature,was confirmed last week by Oregon Health and Science University(OHSU), which collaborated with the Salk Institute and Korea'sInstitute for Basic Science to use a technique known asCRISPR-Cas9 to correct a genetic mutation for a heart condition.Until now, published studies using the technique had beendone in China with mixed results.

CRISPR-Cas9 works as a type of molecular scissors that canselectively trim away unwanted parts of the genome, and replaceit with new stretches of DNA."We have demonstrated the possibility to correct mutationsin a human embryo in a safe way and with a certain degree ofefficiency," said Juan Carlos Izpisua Belmonte, a professor inSalk's Gene Expression Laboratory and a co-author of the study.To increase the success rate, his team introduced the genomeediting components along with sperm from a male with thetargeted gene defect during the in vitro fertilization process.

They found that the embryo used the available healthy copy ofthe gene to repair the mutated part.The Salk/OHSU team also found that its gene correction didnot cause any detectable mutations in other parts of the genome a major concern for gene editing.Still, the technology was not 100 per cent successful it increased the number of repaired embryos from 50 per cent, whichwould have occurred naturally, to 74 per cent.The embryos, tested in the laboratory, were allowed todevelop for only a few days."There is still much to be done to establish the safety ofthe methods, therefore they should not be adopted clinically,"Robin Lovell-Badge, a professor at London's Francis CrickInstitute who was not involved in the study, said in astatement.

Washington's National Academy of Sciences (NAS) earlier thisyear softened its previous opposition to the use of gene editingtechnology in human embryos, which has raised concerns it couldbe used to create so-called designer babies. There is also afear of introducing unintended mutations into the "germline,"meaning cells that become eggs or sperm."No one is thinking about this because it is practicallyimpossible at this point," Izpisua Belmonte said. "This is stillvery basic research let alone something as complex as whatnature has done for millions and millions of years ofevolution."An international group of 11 organizations, including theAmerican Society of Human Genetics and Britain's Wellcome Trust,on Wednesday issued a policy statement recommending againstgenome editing that culminates in human implantation andpregnancy, while supporting publicly funded research into itspotential clinical applications.The latest research involved a gene mutation linked tohypertrophic cardiomyopathy, the most common cause of suddendeath in otherwise healthy young athletes. It affects around 1in 500 people.Salk's Izpisua Belmonte, emphasizing that much more study isneeded, said the most important practical application for thenew technology could be in correcting genetic mutations inbabies either while they are still in utero or right after theyare born."It is crucial that we continue to proceed with the utmostcaution, paying the highest attention to ethicalconsiderations," he said.

Canada's Assisted Human Reproduction Actbans any manipulation of the human genome that can be transmitted to the next generation.

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