How can IVF help prevent inherited diseases?

Shortly, we’ll hear about a new breakthrough that can reduce the risk of mitochondrial disease entirely by completely replacing the defective mitochondria with healthy ones. This is achieved by using a form of IVF - in vitro fertilisation - and a healthy “donor” egg - replete with working mitochondria but devoid of its own genetic material - to fix the problem. The resulting embryo is implanted back into the mother’s womb, and - if all goes according to plan - a normal pregnancy follows. Before diving into the new breakthrough, we called an IVF pioneer to ask how this approach can help prevent inherited conditions…

Robert - I'm Robert Winston. I'm Professor of Science and Society at Imperial College London and, of course, I've been involved with in vitro fertilisation since the very first IVF treatments. We've been able to deal with genetic diseases for some time since pre-implantation genetic diagnosis was undertaken in my own laboratory. What we were able to do was to take a human embryo and remove a single cell or several cells and then look at the DNA which was in the nucleus. And we had a pretty reliable method of making sure that that baby would be free of the inherited disease which was running in that family because, of course, not all the embryos would be affected. 

Selective embryo transfer like this has already helped stop life-limiting conditions like cystic fibrosis from being passed down. But these conditions are carried by the main “genomic” DNA in the cell. So the approach couldn’t help women with faulty mitochondrial DNA - because their eggs, and hence all of the cells in their ensuing embryos, are affected. For these parents, scientists needed a new approach - one that could ensure their embryos are powered by healthy mitochondria. And because the affected woman’s own eggs are all potentially affected, this is where a donor egg, from an unaffected individual - the third person in a three parent embryo - comes in. Robert Winston again…

A woman who is going to be giving birth to a baby with mitochondrial disease has in her egg some of the mitochondria that will cause the disease potentially later on. So what you can do is what's called a nuclear transfer. So what we do actually is to take a single pipette and remove the egg's nucleus, the cell's nucleus, and that then is transferred into another egg from a normal woman who has had no problems genetically. Her egg has been enucleated and you can then put the nucleus straight into that cell and with luck, of course, you'll get a normal embryo developing.

Officially, you're using, if you like, the so-called three-parent family. It's really not, of course, because actually the amount of DNA you're transferring is less than 0.02% of the DNA. As far as we know, you don't change the normal characteristics of the person.

You don't make them more intelligent or super strong or more pleasant to be with. You might, of course, reduce their disease risk and once that's done, once you've done the nuclear transfer, then you actually will want to look at the resulting embryo that you're producing and decide whether it actually is an oral embryo to do the technique that we first started with, which is pre-implantation genetic diagnosis and sample one or two of the embryo's cells to see, in fact, if that embryo really is, in fact, free of any serious mitochondrial disease.