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Scientists Edit Genes of 167 Embryos, the First Such Procedure on Humans in the U.S.The first CRISPR-Cas9 trial on embryos in the United States was by far the biggest trial with the gene-editing tool to edit humans.
The era of CRISPR for humans has begun.
Last week, genetic biologist Shoukhrat Mitalipov and a team of researchers at Oregon Health and Science University (OHSU) successfully edited the genes of 167 human embryos using the medical tool CRISPR-Cas9. According to a report of the study published today in Nature, they targeted a gene in the embryos called MYBPC3 to remove a mutation that can cause a common hereditary heart condition known as hypertrophic cardiomyopathy, which can result in fatal cardiac arrest even in young people and athl
The procedure was conducted on embryos created in the lab for the purpose of testing the CRISPR-Cas9 treatment. The researchers said the method was more successful than anticipated, and that using CRISPR-Cas9 to remove the target mutation should be considered for clinical trials—which would mean implanting the embryos into a mother's womb so the child is born with the genetic alterations.
"With this particular mutation, we've already done the groundwork, so we're probably much closer to clinical applications," Mitalipov said during a press call, according to MIT Technology Review. "Clinical trials would mean actually implanting some of these embryos with the goal of establishing pregnancy and monitoring births of children and hopefully following up with children."
CRISPR stands for clustered regularly interspaced short palindromic repeats. These are segments of DNA and RNA that work with the Cas9 protein to delete and sometimes replace parts of an organism's genome. The process works in three steps. First a segment of RNA is coded with instructions to locate a specific part of the genome by copying that genetic sequence. Then the Cas9 enzyme cuts out that part of the genetic code. As an optional third step, a new DNA segment can be inserted to replace the deleted part of the genome.
In the case of the recent trial at Oregon Health and Science University, researchers deleted a part of the genome that causes a mutation that can lead to hypertrophic cardiomyopathy and filled the gap with a healthy strand of DNA. The embryos were created from eggs donated by healthy women, which were artificially inseminated with sperm from males carrying the mutation. While Chinese researchers have conducted three CRISPR trials on human embryos, the OHSU study was by far the largest procedure with the most embryos modified.
The procedure was most effective when CRISPR-Cas9 was injected into the eggs along with the sperm rather than immediately after. In this case, 42 out of the 58 edited embryos were free of the mutation that causes hypertrophic cardiomyopathy. Under normal circumstances, 50 percent of eggs fertilized by a father carrying the cardiomyopathy mutation will also carry the genetic flaw. Using CRISPR improved that ratio so only about 28 percent received the mutation, and 72 percent became healthy embryos.
However, the 16 embryos that did not become free of the mutation experienced unintended genetic deletions or insertions. This margin of error shows that the CRISPR-Cas9 tool is not perfect, and improvements are still needed.
Proponents of this procedure point out that fathers who carry the mutation can take advantage of such treatments to completely delete the dangerous genetic flaw from the family lineage. Opponents argue that parents can already used established medical processes, such as in vitro fertilization (IVF) and genetic scans, to fertilize eggs in the lab and only implant healthy eggs back into the mother's womb. However, the team that conducted the recent study argues that CRISPR can be used to augment this process and increase the probability of pregnancy.
More importantly, CRISPR-Cas9 has the potential to prevent a myriad of diseases and conditions beyond hypertrophic cardiomyopathy, which affects about 1 in 500 people. Gene editing procedures could also treat patients with sickle cell anemia, HIV, and multiple types of cancers including leukemia and breast cancer. Treating these conditions at an early age, or even before the patient is born, could also result in huge cost savings for the medical industry—the ultimate preventative care.
But there is no shortage of concerns regarding genome editing. Some opponents argue the unforeseen effects present a real danger in these types of procedures, and others worry that disease treatment with gene editing is the first step toward a future of so-called "designer babies."
The regulation of future CRISPR research in the United States remains unclear as well. While genome editing studies are permitted in specific circumstances, such as the OHSU study, clinical trials are still forbade by Congress. In addition, the National Institutes of Health does not fund research on human embryos, which is where CRISPR is most effective at preventing disease. Given these barriers, it is possible U.S. researchers look to other countries to continue their work.
"There is a long road ahead, particularly if you want to do this study in a regulated way," said Mitalipov. "It's unclear at this point when we would be able to move on. We would be supportive to moving this technology to other countries."
Doctors and medical researchers have demonstrated that genome modification can be highly effective at treating and preventing otherwise lethal and permanent human diseases. CRISPR will almost certainly become more commonly used in the future, as institutions around the world prepare to conduct studies of their own. Whether CRISPR is a miracle procedure, humanity's tool to ensuring good health, or if it could cause unforeseen physical and societal consequences, is yet to be seen.
Source: MIT Technology Review