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. 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. “It’s the best way to treat the disease before the genetic mutation is actually transmitted to the embryo.”

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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. “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. 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. 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. “But I think that’s possible to do.”

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He’s also encouraged by the fact that the gene editing and repair did not introduce other errors in the DNA. 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. 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. 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. 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. “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. 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.
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.