How to strike the right balance in talking about the latest experiment in which a gene in a human embryo was edited? Should it be considered the first step on the road to tailored personal genomes, or a useful advance in what might one day be a valuable medical technique? Or just an incremental step in basic science?
This sort of editing of a genome would have been impossible before the advent in 2012-13 of the CRISPR-Cas9 technique, which uses a set of molecular machinery—basically a bacterial DNA-cleaving enzyme—to modify genes on DNA in a precisely targeted manner. So the result is certainly exciting. And because gene editing in human embryos has profound ethical as well as medical implications, it is controversial. Yet at the same time, the potential of doing such work was already apparent from previous experience with CRISPR, and we know very little at this stage about the implications of such a genetic change for the further development of the embryo. No one is talking yet about doing this in clinical medicine or human reproduction. So the furore over “designer babies,” while predictable, is out of proportion to what has been scientifically achieved here.
The new work was carried out by a team in the US, China and South Korea. It is not the first time that CRISPR has been used to genetically modify a human embryo—that was done in 2015 by researchers in China (see this piece)—but the involvement of teams within the more stringent regulatory and ethical regime of the US marks a significant step in acceptance of such experiments. The 2015 Chinese work was rejected by the two major science journals Nature and Science on ethical grounds, so it is notable that Nature has published the new paper. Nonetheless, it was only because the work had private funding in the US (where the main laboratory was at the Oregon Health and Science University in Portland) that it could sidestep government restrictions.
The researchers used IVF techniques to produce embryos from the sperm of a man carrying a mutant form of a gene called MYBPC3, which causes a rare and severe heart disease called hypertrophic cardiomyopathy (HCM). (Because, like most carriers, the man also had the healthy form of the gene—we have two copies of our genes, one inherited from each parent—he does not suffer from the often fatal condition, but is a carrier.)