Scientists Correct Disease-Causing Gene Mutation in Human Embryos

In breakthrough research published on Wednesday, American scientists announced that they had successfully edited disease-causing genes out of human embryos using the gene-editing tool CRISPR.

Scientists at the Salk Institute in collaboration with colleagues in OR and South Korea have succeeded in correcting a disease-causing mutation in human embryos through gene editing.

"Using gene editing during fertilization in this way is a clever idea, especially as we know that human sperm naturally contain a high level of damaged DNA due to environmental and other exposures, which must be repaired by the oocyte as part of fertilization during natural conception", Brison said.

CRISPR, which stands for "clustered regularly interspaced short palindromic repeats", holds promise for correcting mutations in the human genome to prevent genetic disease. The efficiency, accuracy and safety of the approach presented suggest that it has potential to be used for the correction of heritable mutations in human embryos by complementing preimplantation genetic diagnosis.

CRISPR-Cas9 is a gene-editing technique that lets scientists pinpoint, remove and replace a faulty sequence on a strand of DNA. Previous attempts by Chinese researchers were unsuccessful at achieving this without safety concerns.

Jennifer Doudna, a University of California, Berkeley molecular biologist, told the the San Diego Union-Tribune that the recommendations of the National Academy of Science should be respected, saying the ban on clinical trials ought to continue "until there's broad societal consensus about the value". When that was done, 42 out of 58 edited embryos were found to be free of the hypertrophic cardiomyopathy mutation. The United States forbids the use of federal funds for embryo research, and the Food and Drug Administration is prohibited from considering any clinical trials involving genetic modifications that can be inherited.

"The genome editing tools are now not sufficiently efficient and specific to be reliable, and regulatory and oversight processes have not been established", Carroll said, adding that the work on the new study was "well-done" and "well-presented".

It turns out that the embryo relies on the normal copy of the gene, in this case from the egg, to fix the break made when CRISPR cut out the mutated gene. If one version of the bad gene is inherited, that carries the disease forward to the next generation.

However, permitting edits to germ line cells - such as embryos, eggs, and sperm - could also be "very unsafe on multiple levels", DiCamillo warned. Such tinkering with embryo DNA, called germline editing, is controversial because of that the technology will be used to create so-called designer babies.

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Still, the experiment moves the idea of tinkering with genes before birth "from future fantasy to the world of possibility", said Peter Braude, an emeritus professor of obstetrics and gynecology at King's College London. People with the disease carry a mutation in one of two copies of their MYBPC3 gene. Gene correction would rescue mutant embryos, increase the number of embryos available for transfer and ultimately improve pregnancy rates. If US regulators - the Food and Drug Administration - weren't willing to let that happen, the scientists say they'd pursue clinical trials overseas, perhaps in the United Kingdom or elsewhere. The technology, which selectively "snips" and trims areas of the genome and replaces it with strands of desired DNA, has previously been used on adult humans and other species.

Injecting Cas9 along with the sperm - before an egg had a chance to replicate its DNA - produced only one patchwork embryo.

In each case, eggs obtained from healthy donors were fertilized with sperm from a single man carrying the cardiomyopathy mutation.

It is one of 10,000 inherited diseases that are caused by a single defective gene, like BRCA1 and BRCA2.

"These researchers have really taken it upon themselves to advance this technology this way without asking the rest of us if we really want to go along". The work was consistent with recommendations issued this year by the National Academy of Sciences and the National Academy of Medicine joint panel on human genome editing.

Scientists claim if these healthy embryos were implanted into a woman's womb, future generations would no longer inherit the illness.

The scientists in OR obtained the eggs for the research and brought their expertise in embryo biology to the study.

The first study, published in 2015, attempted to fix a defective gene causing the blood disease beta thalassemia.