A team of biologists in Oregon for the first time have successfully edited genes in human embryos to correct a heritable disease-causing mutation, according to a study published Wednesday in the journal Nature. 

The experiment, first reported last week in MIT Technology Review, is not the first of its kind: Three previous studies that used CRISPR to edit human embryos were all conducted in China. However, it is the first such study completed in the United States, and the scope of the study goes beyond the previous research in terms of the number of embryos tested and the research findings.

None of the embryos involved in the study developed for more than a few days, and researchers never intended to implant any of them into a womb, according to the Technology Review. Congress has barred FDA from approving any clinical trials using genome-editing technology in human embryos.

Study details

For the study, researchers at Oregon Health and Science University worked with researchers in California, China, and South Korea to see whether they could use the gene-editing tool CRISPR to successfully edit out a gene mutation in human embryos that causes hypertrophic cardiomyopathy—a genetic heart condition that can have no symptoms and is known for causing sudden death in young competitive athletes. According to the Washington Post's "To Your Health," the disease affects 1 in 500 people around the globe.

Both FDA and the National Institutes of Health are currently prohibited from funding such research. As such, the latest study was funded by Oregon Health and Science University, the Institute for Basic Science in South Korea, and several foundations, according to the New York Times.

The research involved eggs from 12 healthy female donors and sperm from a male donor who has the gene mutation. The researchers used CRISPR to edit the genetic mutation during the in vitro fertilization process.

Findings

The researchers noted that absent genetic modification, embryos have a 50 percent chance of not having the disease-causing mutation if one biological parent is a carrier. Using CRISPR, they were able to increase those odds to 72 percent. Further, they found the successfully CRISPR-edited embryos did not contain editing errors or unintended DNA changes that arose in previous studies.

According to the Technology Review, the latest experiment may have had more success than past research by "'getting in early' and injecting CRISPR into the eggs at the same time they were fertilized with sperm."

Shoukhrat Mitalipov, director of the Oregon Health and Science University Center for Embryonic Cell and Gene Therapy and senior author of the study, said he believed the odds of achieving a mutation-free gene could reach 90 percent after the process is fine-tuned.

The researchers also said they were surprised by the way the CRISPR-edited embryos repaired themselves. Instead of copying a healthy, lab-grown heart gene introduced by the scientists, the embryo's cells copied the DNA sequence from the healthy genetic material in the donor eggs. Juan Carlos Izpisua Belmonte, a professor in Salk's Gene Expression Laboratory and a co-author of the study, said, "We have demonstrated the possibility to correct mutations in a human embryo in a safe way and with a certain degree of efficiency."

Discussion

Scientists and ethicists have expressed a range of sentiments over such experiments—from awe to alarm, the Technology Review reports.

While scientists say the approach could one day be used to avoid genetic diseases—such as breast and ovarian cancer, and diseases such as Huntington's, Tay-Sachs, and sickle cell anemia—some have raised concerns that it could lead to "designer babies." Further, according to STAT News, some fear that "such manipulations could alter the course of human evolution" because the edited cells could be passed down to future generations, if a germline edited embryo were implanted, born, and grown to adulthood.

However, R. Alta Charo, a legal scholar and bioethicist at the University of Wisconsin, Madison, said, "We still have regulatory barriers in the United States to ever trying this to achieve a pregnancy," adding that the public would have "plenty of time" to weigh in on whether such embryos should be implanted in a womb.

Charo said the study "is the kind of research that is essential if we are to know if it's possible to safely and precisely make corrections" in human embryos. She added that "while there will be time for the public to decide if they want to get rid of regulatory obstacles to these studies, [she does] not find them inherently unethical."

The National Academy of Sciences (NAS) and the National Academy of Medicine earlier this year gave the first green light to such research, saying scientific advancements have made the use of gene-editing technology on human reproductive cells "a realistic possibility that deserves serious consideration." But the groups said such research would need to be strictly regulated.  

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

According to Reuters, an international group of 11 organizations, including the American Society of Human Genetics, issued a policy statement Wednesday said they support publicly funded research into the clinical uses of genome editing in human embryos, but recommended against implanting such embryos for pregnancy.

Robert C. Green, a medical geneticist at Harvard Medical School, called the prospect of editing embryos to avoid disease "inevitable and exciting." He said that "with proper controls in place, it's going to lead to huge advances in human health" (Beasley, Reuters, 8/2; Belluck, New York Times, 8/2; Eunjung Cha, "To Your Health," Washington Post, 8/2; Dockser Marcus, Wall Street Journal, 8/2; Begley, STAT News, 7/26; Beasley, Reuters, 7/27; Connor, MIT Technology Review, 7/26; AP/New York Times, 7/27).

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