Scientists fix heart disease mutation in human embryos using CRISPR

Last week the scientific community was buzzing with the news that US scientists had genetically modified human embryos using CRISPR gene editing technology. While the story broke before the research was published, many journalists and news outlets weighed in on the study’s findings and the ethical implications they raise. We covered this initial burst of news in last week’s stem cell stories that caught our eye.

Shoukhrat Mitalipov (Leah Nash, New York Times)

After a week of suspense, the highly-anticipated study was published yesterday in the journal Nature. The work was led by senior author Dr. Shoukhrat Mitalipov from Oregon Health and Sciences University (and a member of CIRM’s Grants Working Group, the panel of experts who review applications to us for funding) in collaboration with scientists from the Salk Institute and Korea’s Institute for Basic Science.

In brief, the study revealed that the teams’ CRISPR technology could correct a genetic mutation that causes a disease called hypertrophic cardiomyopathy (HCM) in 72% of human embryos without causing off-target effects, which are unwanted genome modifications caused by CRISPR. These findings are a big improvement over previous studies by other groups that had issues with off-target effects and mosaicism, where CRISPR only correctly modifies mutations in some but not all cells in an embryo.

Newly fertilized eggs before gene editing, left, and embryos after gene editing and a few rounds of cell division. (Image from Shoukrat Mitalipov in New York Times)

Mitalipov spoke to STATnews about a particularly interesting discovery that he and the other scientists made in the Nature study,

“The main finding is that the CRISPR’d embryos did not accept the “repair DNA” that the scientists expected them to use as a replacement for the mutated gene deleted by CRISPR, which the embryos inherited from their father. Instead, the embryos used the mother’s version of the gene, called the homologue.”

Sharon Begley, the author of the STATnews article, argued that this discovery means that “designer babies” aren’t just around the corner.

“If embryos resist taking up synthetic DNA after CRISPR has deleted an unwanted gene, then “designer babies,” created by inserting a gene for a desirable trait into an embryo, will likely be more difficult than expected.”

Ed Yong from the Atlantic also took a similar stance towards Mitalipov’s study in his article titled “The Designer Baby Era is Not Upon Us”. He wrote,

“The bigger worry is that gene-editing could be used to make people stronger, smarter, or taller, paving the way for a new eugenics, and widening the already substantial gaps between the wealthy and poor. But many geneticists believe that such a future is fundamentally unlikely because complex traits like height and intelligence are the work of hundreds or thousands of genes, each of which have a tiny effect. The prospect of editing them all is implausible. And since genes are so thoroughly interconnected, it may be impossible to edit one particular trait without also affecting many others.”

Dr. Juan Carlos Izpisua Belmonte, who’s a corresponding author on the paper and a former CIRM grantee from the Salk Institute, commented on the impact that this research could have on human health in a Salk news release.

Co-authors Juan Carlos Izpisua Belmonte and Jun Wu. (Salk Institute)

“Thanks to advances in stem cell technologies and gene editing, we are finally starting to address disease-causing mutations that impact potentially millions of people. Gene editing is still in its infancy so even though this preliminary effort was found to be safe and effective, it is crucial that we continue to proceed with the utmost caution, paying the highest attention to ethical considerations.”

Pam Belluck from The New York Times also suggested that this research could have a significant impact on how we prevent disease in newborns.

“This research marks a major milestone and, while a long way from clinical use, it raises the prospect that gene editing may one day protect babies from a variety of hereditary conditions.”

So when will the dawn of CRISPR babies arrive? Ed Yong took a stab at answering this million dollar question with help from experts in the field.

“Not for a while. The technique would need to be refined, tested on non-human primates, and shown to be safe. “The safety studies would likely take 10 to 15 years before FDA or other regulators would even consider allowing clinical trials,” wrote bioethicist Hank Greely in a piece for Scientific American. “The Mitalipov research could mean that moment is 9 years and 10 months away instead of 10 years, but it is not close.” In the meantime, Mitalipov’s colleague Sanjiv Kaul says, “We’ll get the method to perfection so that when it’s possible to use it in a clinical trial, we can.”

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