Does the editing approach have limitations?
Yes, and they are important ones. CRISPR works by cutting DNA at a precise point. A cell then uses a matching piece of DNA as a template for repairing the cut. It’s like tearing a misprinted page from a book and using a pristine edition to fill out the missing text. Mitalipov’s team offered the embryos a pristine copy of the MYBPC3 gene to be used in the repair process. But to their surprise, the embryos largely ignored this gift. Instead, they used the healthy copy of the gene from the egg to repair the CRISPR-sliced mutant version from the sperm. That means that this technique would not work if both parents have HCM. If both pass a mutant version of MYBPC3 to an embryo, there’s no healthy copy to use as a template. “We still need to figure out how to correct those,” says Mitalipov.
When can we expect such editing to be commonplace?
Not for a while. The technique would need to be refined, tested on non-human primates, and shown to be safe. “The safety studies would likely take 10 to 15 years before FDA or other regulators would even consider allowing clinical trials,” wrote bioethicist Hank Greely in a piece for Scientific American. “The Mitalipov research could mean that moment is 9 years and 10 months away instead of 10 years, but it is not close.” In the meantime, Kaul says, “We’ll get the method to perfection so that when it’s possible to use it in a clinical trial, we can.”
Isn’t this a slippery slope toward making designer babies?
In terms of avoiding genetic diseases, it’s not conceptually different from PGD, which is already widely used. The bigger worry is that gene-editing could be used to make people stronger, smarter, or taller, paving the way for a new eugenics, and widening the already substantial gaps between the wealthy and poor. But many geneticists believe that such a future is fundamentally unlikely because complex traits like height and intelligence are the work of hundreds or thousands of genes, each of which have a tiny effect. The prospect of editing them all is implausible. And since genes are so thoroughly interconnected, it may be impossible to edit one particular trait without also affecting many others.
“There’s the worry that this could be used for enhancement, so society has to draw a line,” says Mitalipov. “But this is pretty complex technology and it wouldn’t be hard to regulate it.”
Wait, haven’t I read about DIY gene-editors, who are using CRISPR in their basement labs?
Yes, but none of those people are using the technique to edit human embryos. Mitalipov’s work is essentially a form of IVF. “It’s not simple IVF either,” he says. “Everything needs to be done exactly the way we did it. You’d need to do a biopsy with every embryo to screen for off-target mutations. You can’t do it at home.”