BIG QUESTION OF THE MONTH: Should we use CRISPR, the new technique that enables precise DNA editing, to change the genes of human embryos to eradicate disease--or even to enhance desirable traits? LeapsMag invited three leading experts to weigh in.
CRISPR is producing an important revolution in the biosciences, a revolution that will change our world in fundamental ways. Its implications need to be discussed and debated, and not just by scientists and ethicists. Unfortunately, so far we are debating the wrong issues.
Controversy has raged about editing human genes, particularly the DNA of embryos that could pass the changes down to their descendants. This technology, human germline editing, seems highly unlikely to be broadly available for at least the next few decades; if and when it is, it may well be unimportant.
Human germline editing is unlikely to happen soon because it has important safety risks but almost no significant benefits.
Human germline editing is unlikely to happen soon because it has important safety risks but almost no significant benefits. The risks – harm to babies – are compelling. We care a lot about babies. A technology that worked 95 percent of the time (and produced disabled or dying infants "only" five percent of the time) would be a disaster. Our concern for babies will lead, at the least, to rigorous legal requirements for preapproval safety testing. Many countries will just impose flat bans.
But these risks also have implications beyond safety regulation. For this technology to take off, physicians, assisted reproduction clinics, and geneticists will have to be willing to put their reputations – and their malpractice liability – on the line. And prospective mothers will have to be willing to take unknown risks with their children.
Sometimes, large and unknown risks are worth taking, but not here. For the next few decades, human germline editing offers almost no substantial benefits, for health or for enhancement.
Prospective parents already have a tried and true alternative to avoid having children with genetic diseases: preimplantation genetic diagnosis (PGD). In PGD, clinicians remove cells from three- to five-day-old embryos. Those cells are then tested to see which embryos would inherit the disease and which would not. This technology has been in use for over 27 years and is safe and effective. Rather than engaging in editing an embryo's disease-causing DNA, parents can just select embryos without those DNA variations. For so-called autosomal recessive diseases, three out of four embryos, on average, will be disease free; for autosomal dominant diseases, half will be.
Only a handful of prospective parents would need to use gene editing to avoid genetic disease.
Couples where each has the same recessive condition (cystic fibrosis) or where one of them has the terrible luck to have two copies of the DNA variant for a dominant disease (Huntington's disease). In those cases, the prospective parents would need to stay alive long enough to be able, and be sufficiently healthy to want, to have children. In a world of 7.3 billion humans, there will be some such cases, but they will probably be no more than a few thousand – or hundred.
People are also concerned about germline editing for genetic enhancement. But this is also unlikely anytime soon. We know basically nothing about genetic variations that enhance people beyond normal. For example, we know hundreds of genes that, when damaged, affect intelligence – but these all cause very low intelligence. We know of no variations that non-trivially increase it.
Over the next few decades, we might (or might not) learn about complex diseases where several genes are involved, making embryo selection less useful. And we might (or might not) learn about genetic enhancements involving DNA sequences not typically found in prospective parents and so not available to embryo selection. By that time, the safety issues could be resolved.
And, even then, how worried should we be – and about what? A bit, but not very and not about much.
"The human germline genome is not the holy essence of humanity."
The human germline genome is not the holy essence of humanity. For one thing, it doesn't really exist. There are 7.3 billion human germline genomes; each of us has a different one. And those genomes change every generation. I do not have exactly the same genetic variations my parents received from my grandparents; my children do not have exactly the ones I received from my parents. The DNA changed, through mutation, during each generation.
And our editing will usually be insignificant in the context of the whole human genome. For medical purposes, we will change some rare DNA variations that cause disease into the much more common DNA variations that do not cause disease. Rare, nasty variants will become rarer, but civilization changes these frequencies all the time. For instance, the use of insulin has increased the number of people with DNA variations that predispose people to type 1 ("juvenile") diabetes – because now those people live long enough to reproduce. Even agriculture changed our DNA, leading, for example, to more copies of starch-digesting genes. And, in any event, what is the meaningful difference between "fixing" a disease gene in an embryo or waiting to fix it with gene therapy in a born baby . . . other than avoiding the need to repeat the gene therapy in the next generation?
If genetic enhancement ever becomes possible in a non-trivial way, it would raise important questions, but questions about enhancement generally and not fundamentally about genetics. Enhancement through drugs, prosthetics, brain-computer interfaces, genes, or tools (like the laptop I wrote this on) all raise similar ethical issues. We can use the decades we will have to try to think more systematically about the ethical and policy issues for all enhancements. We should not panic about germline genetic enhancement.
One superficially appealing argument is that we are not wise enough to change our own genomes. This ignores the fact that we have been changing our genomes, inadvertently, since at least the dawn of civilization. We do not have to be wise enough to change our genome perfectly; we just need to be wise enough to change it better than the random and unforeseen ways we change it now. That should not be beyond our power.
Human germline editing will not be a concern for several decades and it may never be an important concern. What should we be paying attention to?
Non-human genome editing. Governments, researchers, and even do-it-yourself hobbyists can use CRISPR, especially when coupled with a technique called "gene drive," to change the genomes of whole species of living things – domestic or wild; animal, vegetable, or microbial – cheaply, easily, and before we even know it is happening. We care much less about mosquito babies than human ones and our legal structures are not built for wise and nuanced regulation of this kind of genome editing. Those issues demand our urgent attention – if we can tear ourselves away from dramatic but less important visions of "designer babies."