Later this year, legislators in the UK will vote on (and almost certainly pass) a bill to begin human testing on a new technique of so-called “three-parent” in-vitro fertilization. To understand why this might be helpful, and how a third parent can be medically useful, you need to understand the basics of genetic inheritance. The most important single insight is this: an egg is the factory of human life, while a sperm is just a nucleus with an outboard motor.
Most people are taught in school that the genetic material of a cell is found in the nucleus, protected and packaged up into 23 tidy chromosome-pairs. This is only mostly true, however — the cell actually stores extra genetic information in the mitochondria, the cell’s power stations. Since sperm are literally just moving nuclei, a fetus thus derives 100% of its mitochondrial DNA from the egg (and thus from the mother). Mitochondrial inheritance is so untouched by males that biologists have developed the idea of Mitochondrial Eve, the hypothetical proto-human female from whom all modern mitochondrial DNA is derived. (Click if you’re interested in where mitochondria come from.)
So doctors were faced with millions of couples whose children would definitely inherit a diseased mitochondrial gene, but that gene would be physically separated from the larger primary genome. The solution is rather obvious: replace an egg’s diseased mitochondria with healthy ones before fertilization, and you should cause very few problems while solving very many. Since this would be a full replacement of this secondary genome, it really doesn’t matter how many mitochondrial diseases you carry, as this single treatment would prevent them all from being passed on.
If you’re keeping track, this means that we would technically have children with three parents. That is, we are about to start creating babies with one nuclear mother and one nuclear father, along with a separate mitochondrial mother. As noted, replacing mitochondrial DNA will have a lesser impact than replacing any other sort of DNA, but don’t think that this is a loophole discovery or an overblown headline: in every way that matters, these children will have three distinct parents. Interestingly, while the father does carry mitochondria (in every cell but the sperm), it seems mitochondria taken from female egg cells are the best for this treatment.
Prior research on this procedure has found no negative effects in mice or chimps, while dead-end studies with infertile egg human cells have also been fruitful. The team is adamant that it’s time to begin real human trials — but this brings up some quandaries. Specifically, while ending genetic diseases is of course a noble goal, perhaps simple screening and reproductive restraint is the best response; while it’s terrible for anyone to be restrained from breeding normally, are the hardships of adoption or surrogacy really so bad that we can justify potentially horrific lines of experimentation? How much do we, and should we, really value the right to biologically create a child, as opposed to just having one via any safe and approved avenue?
To be clear, everything we know says that this research should be safe — but what if it isn’t? We’re at a very dangerous point in genetic research, and literally one deformed baby will destroy any productive discussion we might be able to have on the topic. Three-parent babies would probably work, but there is enormous potential for backlash over anything less than complete and total success. Research doesn’t generally progress that way, and human life has always been viewed as too sacred for such learning-by-doing.
On the other hand, if we save millions of lives in the long term, will we care about the failed IVF pregnancies that led to them? Ask yourself these questions seriously, because I guarantee you it’ll be on the news within 10 years, and probably less. Probably a lot less.