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Salk Scientists Contribute To First Gene Editing Of Human Embryos In US
Wednesday, August 2, 2017
Credit: Salk Institute
Salk Scientists Contribute To First Gene Editing Of Human Embryos In US
David Wagner, science reporter, KPBS
Salk scientists were involved in a new study that raises the possibility of curing certain genetic diseases in future generations. But the prospect of editing a child's DNA before they are born remains very controversial.
Scientists at the Salk Institute in La Jolla have helped to edit the DNA of human embryos for the first time in the United States.
They contributed to a study published Wednesday in the journal Nature showing that a mutation linked with a deadly, inherited heart disease can be successfully corrected in early-stage embryos using the gene editing tool CRISPR.
The researchers, led by Shoukhrat Mitalipov at the Oregon Health & Science University, say their results suggest CRIPSR could be a powerful technique for correcting disease-causing genetic mutations in developing human embryos.
But in an interview with KPBS, a Salk scientist involved in the study said more scientific work and ethical consideration is needed before using this approach in the creation of any future human children.
"We need much more basic studies like this to answer the question of whether this is a feasible approach," said Salk staff scientist Jun Wu, who contributed to the study along with Salk researchers Juan Carlos Izpisua Belmonte and Keiichiro Suzuki.
"At this stage, I would say this is still basic research," Wu said. "And we need more basic research like this before we can even consider going forward."
The scientists targeted a mutation in the gene MYBPC3. Having one bad copy of this gene can lead to heart failure and sudden death. The disease affects 1 in 500 people, and is a leading cause of death in otherwise healthy athletes. A patient with this mutation donated his sperm and skin cells for the study.
The scientists in Oregon obtained the eggs for the research and brought their expertise in embryo biology to the study. The Salk scientists contributed by developing the gene editing strategy, initially testing it in stem cells derived from the patient's skin cells.
In 2015, scientists in China conducted the first known attempt to use CRISPR on human embryos. But they found that their edits were imprecise.
Those results raised concerns that any effort to manipulate genes in a human embryo could lead to unintended edits in other genes — known as "off-target effects" — or could lead to embryos containing a mixture of cells with corrected genes and cells with uncorrected genes, a problem known as "mosaicism" that could end up failing to prevent disease.
Wu and his colleagues were able to avoid these problems in their experiments, leading other scientists to describe their results as a "step forward" in comparison to previous studies.
"The very low level of off-target effects (actually apparently not distinguishable from background genomic variation) is very encouraging for future applications," said MIT scientist Richard Hynes, who co-chaired a National Academy of Sciences report on human genome editing released earlier this year.
"Their method is not yet proven to work for other genes and is not yet 100 percent efficient," Hynes wrote in an email to KPBS. "So more work would be needed before this could potentially be used for heritable germline editing."
Wu said timing was key for preventing off-target effects and mosaicism. The scientists made the gene edits early in the embryos' development and saw the efficiency of DNA correction go up.
"We delivered the editing tools earlier. At the one-cell stage, the embryo has enough time to make the repair before they make copies of the DNA," Wu said.
Scientists contacted by KPBS saw these results as a small yet successful step toward the development of new strategies for fighting genetic diseases in future generations. But the prospect of editing a child's DNA before they are born remains very controversial.
Because these edits would not only affect that child, but could also be passed down to their descendants, some ethicists are firmly opposed to editing of the human "germline." In a 2015 statement regarding its policy against funding research on gene-editing in human embryos, the National Institutes of Health said germline editing "has been viewed almost universally as a line that should not be crossed."
The Salk scientists and their colleagues say they never intended to implant any of the embryos used in their research, much less to bring any of those embryos to term. Their work was largely funded by private donations and university money.
Other strategies currently exist for preventing genetic diseases in offspring. Embryos can be genetically screened before they are implanted during in vitro fertilization.
But the scientists note that in certain rare cases, existing strategies are not enough to help parents conceive a child free of a genetic disease. They say it remains to be seen in future studies whether this approach will be successful at correcting other mutations.
"One thing clear at this stage is that we shouldn't apply this technology in any shape or form toward designer babies," Wu said. "The technology is not there yet. And even if it was there, there is still a lot of ethical considerations and scientific limitations. For many of the traits that people want in their next generation, there's not a single underlying gene."
Ethicists told KPBS the researchers have not raised any new problems that were not already known prior to the study's publication.
"This is not the dawn of the era of the designer baby," said University of Wisconsin bioethicist and law professor Alta Charo in an email. "The need for embryo editing to avoid passing a serious disorder to one's children is limited to a small number of situations. In addition, we are already in clinical trials for use of editing to treat diseases in those already born."
Michael Kalichman, director of the Research Ethics Program at UC San Diego, agreed that the study did not signal that parents will soon have the option to pick and choose from a menu of desired traits for their offspring.
"Although it implies a future in which we could choose to have children without particular genetic diseases, or even design for particular traits, that is still likely a very long time from now," he wrote in an email to KPBS.
"On the other hand, the trajectory is for this technology to be sufficiently robust that it will eventually be used," Kalichman wrote. "In anticipation of that use, it is essential that the general public, not just the scientists and clinicians, needs to learn about and consider the implications of the potential applications."
This is not the first time Wu and his Salk colleagues have been involved in research that, even if it has not crossed ethical lines, has raised ethical questions. Earlier this year, they reported creating partially human pig embryos as a way to explore the idea of growing humanized organs in animals in order to address shortages of transplantable organs.
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