When asked why he wanted to climb Mount Everest, George Mallory famously quipped, “Because it’s there.” Today, a group of scientists, led by Shoukhrat Mitalipov at the Oregon Health & Science University, report in the journal Nature the successful use of a gene editing technology to correct a disease-causing mutation in viable human embryos. As biologists early in our career, we are skeptical that their motivation is any better than Mallory’s—and their endeavor comes with greater ethical concerns.
The focus of this study is a single mutation in the gene MYBPC3. This error is “dominant”—a child that inherits just one copy of the mutant gene is at high risk for a serious disease called hypertrophic cardiomyopathy, which can cause sudden cardiac death. Since each person has two gene copies and receives one randomly from each parent, a child with an affected father or mother has a 50 percent chance of inheriting the disease.
Using a gene editing technology called CRISPR/Cas9, Mitalipov and colleagues repaired the mutations in embryos created through in vitro fertilization (IVF) using sperm from a patient with the mutation and eggs from healthy donors. The key innovation of this study was simultaneously injecting the CRISPR machinery and a single sperm into an egg using an established IVF technique. Out of 58 embryos tested, 72 percent were mutation-free, compared with 50 percent of embryos in the control group. The edited embryos also appeared to develop normally until they were destroyed three days later. Importantly, the researchers did not detect any “mosaic” embryos, containing corrections in some but not all of their cells, or unintended mutations in other parts of the genome—challenges highlighted by a controversial 2015 study that attempted similar edits of nonviable embryos.
Since details of this study were leaked last week in the MIT Technology Review, there have been renewed calls to carefully consider the ethics of making heritable gene edits to embryos, eggs, and sperm. Concerns range from off-target effects and the inability of future generations to consent to genetic editing to the potential for Gattaca-style “designer babies.” In response, it has been correctly pointed out that the simplest clinical application is at least a decade off, and using CRISPR on embryos, eggs, and sperm, in contrast to other types of cells, is opposed by much of the scientific community.
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