I’ve written several times in the past years about how new technologies have raised the prospects of a child having three genetically related parents. Most of the discussion has occurred in the UK, but the debate has now reached the US.
The idea here is that egg cells have both mitochondrial and nuclear DNA. Mitochondrial DNA is passed from only from mother to child (and indeed, as I recall it is used to track lineages, sometimes over hundreds of years.) Fathers do not contribute mitochondrial DNA.
Nuclear DNA in an egg combines with DNA from the sperm when the egg is fertilized. Nuclear DNA controls virtually all of the things we think about when we think about genetic heritability–height, weight, eye color, hair color and so on. I believe that, to the extent more complicated things are also controlled by DNA (say tendency towards cancer or alcoholism) it is also nuclear DNA that matters.
But mitochondrial DNA is important. In particular it can matter because there are diseases that are transmitted via mitochondrial DNA. And a woman who carries these diseases will pass them on to her children.
As the earlier posts discuss, this has spurred the development of techniques where the nucleus of an egg cell with healthy mitochondrial DNA is extracted and replaced with the nucleus of an egg from a woman with problematic mitochondrial DNA. The end result is an egg that has healthy mitochondrial DNA.
This egg can then be used in IVF to create an embryo. That embryo will have genetic material from three people–one male who provided the sperm, and two females, one who provided mitochondrial DNA and the other who provided nuclear DNA.
The article and the earlier posts sum up the controversy, I think. I’d only stress that there are two separate questions here. I think we’d do well to keep them separate in discussions.
First, there is a question of safety/readiness of technology. I don’t want to minimize these questions, but in the end they seem to me less interesting for discussion. All medical advances have to be tested for safety before you move to using them on people. And we frequently have debates about whether technologies are safe enough. We know what that debate looks/sounds like.
The second issue, it seems to me, is more unusual–it’s the issue of ethics/eugenics. Is this a dangerous step on a path to designer babies? Here I think the discussion is particularly interesting.
One bioethicist–Sheldon Krimsky–makes an argument that resonate with other discussions here. His general observation is that this technology is potentially quite troubling and also unnecessary. If he’s right about being unnecessary, then of course it is much easier to conclude that the troubling technology should be rejected.
In support of his position that it is unnecessary, he makes two points. First, he identified PIGD (that’s preimplantation genetic diagnosis) as a technology that ensures that embryos with more defective mitochondrial DNA could be weeded out. (I wonder about this because as I understand it, all of the eggs that a woman produces would have the same mitochondrial defects, unless they were random mutations.)
But more importantly, Dr. Krimsky observes that you could avoid this problem just by using donor eggs–eggs from someone who didn’t have any mitochondrial DNA issues. Yet Dr. Krimsky recognizes the Achilles heel of this argument:
“There’s that genetic chauvinism that says unless my DNA is in the child, it will not be truly my child,” he said.
It is “genetic chauvinism” (as Dr. Krimsky calls it) that is driving the demand for this technology.
That sentiment (I’m not sure I’ll call it genetic chauvinism myself) is frequently expressed here. So I think it’s important to recognize that this demand for technology is a driven by that very view. The insistence that only those who are genetically related are the real parents of the child, that all other sorts of parents are somehow false or secondary reinforces the assertion that only a genetic child will do and so, access to the technology is indispensable.