The advances in this field – and the potential dangers they pose – were highlighted last year when Chinese scientist He Jiankui claimed he had made gene edits to a pair of twins to make them immune to AIDS. His work has been internationally condemned, and Chinese authorities went so far as to call it “abominable in nature”.
However, this has not stopped other scientists from pursuing their own research. A team from the Broad Institute of MIT and Harvard recently announced that they have developed a new gene-editing technology that could potentially correct up to 89% of genetic defects, including those that cause diseases like sickle cell anemia. Called “prime editing”, this technique allows for entire sections of DNA strands to be found and replaced, without disruptive breaks or donor DNA.
Prime editing builds on Crispr gene editing, the method used by He Jiankui. Crispr editing works like “molecular scissors” which home in on a particular DNA sequence and then cut it in two. The procedure allows scientists to disable specific genes and correct harmful mutations by providing cells with fresh strands of DNA with which to repair the cut. However, Crispr often leads to cells with a haphazard mix of edits, including extra chunks of DNA, or missing chunks of genetic code.
Prime editing is more precise and versatile, the researchers say, “directly writing new genetic information into a specified DNA site”. Writing in the journal Nature, the scientists described their success in making 175 different DNA edits to human cells with “impressive precision”. In one case, they corrected mutations that cause the inherited blood disorder sickle cell anaemia. In another, they removed the four extra DNA letters in a particular gene that cause Tay-Sachs disease, a rare condition that destroys children’s nerves and usually proves fatal by five years old.
The scientists stress that they are a long way from being able to move away from tissue cultivated in the lab to human subjects, but they aim to continue testing on different models of diseases to ultimately “provide a potential path for human therapeutic applications”. However, a Russian geneticist, Denis Rebrikov, has already announced plans to alter the DNA in human embryos with CRISPR, and then implant them so they can develop into babies.
He says that he plans to seek rigorous ethical and regulatory review, and will focus on treating inherited deafness. His detractors point out that cochlear implants are already extremely effective at mitigating the effects of the condition he wants to treat with the gene splicing, and that his call for volunteers is in itself unethical because the technology is not ready for human testing.
These criticisms are the same that have been raised about Crispr before. Some scientists have said that it could open the door to human embryos being manipulated for nontherapeutic reasons, or that it could create unintended mutations and new diseases. In March this year, a group of researchers, including the scientist who pioneered and patented Crispr technology, called for a global moratorium on human germline editing – changes made to inherited DNA that can be passed on to the next generation.
Whether they succeed in getting the world’s governments to agree to the moratorium or not, the genie is already out of the bottle. The technology may still be in its early days, but all of these trials and research bring us one step closer to being able to create made-to-order babies. In addition to removing the propensity for genetic diseases, we could demand that our children grow to reach a certain height or have a certain eye colour. And even if (and when) the technology is regulated, there will always be unethical doctors and clinics who will perform the procedure illegally.