Lab tests show risks of using CRISPR gene editing on embryos

A laboratory experiment to fix defective DNA in human embryos shows what can go wrong with this type of gene editing and why leading scientists say it is too unsafe to try. In more than half of the cases, editing caused unintended changes, such as B. the loss of an entire chromosome or large parts of it.
Columbia University researchers described their work in Cell on Thursday. They used CRISPR-cas9, the same chemical tool a Chinese scientist used on embryos in 2018 to create the world's first gene-edited babies, which put him in prison and aroused international contempt.
This tool allows scientists to cut DNA at a precise point and has great potential for good - it's already being used to raise better plants and animals, it makes promises to treat diseases, and earned its discoverers a Nobel Prize earlier this month.
However, its use on embryos, sperm or eggs leads to changes that can pass to future generations. Several international panels of scientists and ethicists have said it is too early to know if it can be done safely, and Columbia’s new work highlights the potential harm.
"If our results had been known two years ago, I doubt that anyone would have acted," said the biologist Dieter Egli, who led the study.
The researchers created 40 embryos using eggs from healthy donors and sperm from a man with a gene mutation - a single letter is missing from the DNA alphabet - that causes blindness. Editing aimed to add the missing letter to make the gene work.
Processing of some embryos was attempted at fertilization, which was considered the best time for such attempts. Other embryos were processed when they contained two cells and were almost two days old. The cells at various stages of development were then analyzed to see how many had repaired the mutation.
Surprisingly, it did not work in any of the cells in embryos that were processed at fertilization. It only worked in three of the 45 cells from embryos that were processed at a later date.
In many other cases, "we've found that instead of fixing the mutation, the chromosome that carries the mutation has disappeared" - a profound change that is likely to doom the embryo, Egli said. Many other cells showed changes in other chromosomes that could do harm as well.
Previous researchers who believed they had repaired a defect in embryos may have been misled because they were successful because standard laboratory tests failed to detect the mutation. However, more extensive tests, such as those done in this study, show that other changes could have occurred, such as the obliteration of an entire chromosome, Egli said.
The new work suggests that gene editing could show promise in correcting disorders caused by an extra copy of a chromosome such as Down syndrome. The danger revealed in the new study "further confirms that we are unwilling, not even near" to try, Dr. Eric Topol in an email.
"This takes the concerns already expressed about human embryo manipulation to another level," added Topol, who heads the Scripps Research Translational Institute in San Diego and was not part of the new work.
In the US, federal funds cannot be used for research on human embryos. Therefore, the Columbia researchers used private money from two foundations. Some of the scientists are affiliated with gene therapy or analysis companies.
The Associated Press Department of Health and Science is supported by the Department of Science Education of the Howard Hughes Medical Institute. The AP is solely responsible for all content.

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