Britain’s House of Commons has approved, by an overwhelming majority, to allow a form of technology that involves replacing the nucleus of one woman’s egg with the nucleus of another to be used in so-called “three-parent IVF.”
This vote has been wrought with controversy. Many people are hopeful that this technology will help those women with mitochondrial disease to have biological children without passing on their mitochondrial DNA. Others are concerned about the long-term consequences that this procedure will have on the children born from it.
In November of 2013, I wrote an article about mitochondrial screening and three-parent IVF for bioethics.com that discusses the science and the bioethical issues behind these techniques. It also provides a some background information on mitochondria. The issues raised in this article remain relevant to today’s vote. I do want to add a comment about something that has appeared in recent media reports.
Julian Savulescu, ethicist at Oxford, said in a recent article in The Guardian that the technology used for “three-parent IVF” is akin to micro-organ, or organelle, donation. Arthur Caplan, medical ethicist at NYU, in an article in Wired, also likened this technology to a kind of organ donation. However, replacing the nucleus of an egg with another is not analogous to organ donation, or stem cell donation, because this kind of procedure changes the germ line. In other words, the results from replacing the nucleus in an egg cell changes not only the child born from the subsequent IVF procedure, but the children that come from this child, and so on down the generational line.
With something like a kidney transplant or a stem cell transplant, the procedure does not introduce the donor’s DNA into the recipient’s gametes, and thus, does not incorporate new DNA into the germ line. If the recipient has children after receiving an organ or stem cell donation, he or she will not pass the donor’s DNA along to the child.
Some would consider the multi-generational effect from this nuclear transfer procedure beneficial because it means that mitochondrial disease is not passed down to the next generation. Others are concerned that any unforeseen problems that emerge later would be perpetuated down the generational line. Even though there have been studies with primates and human embryos, we cannot truly know if there will be long-term negative effects until it is done on a human embryo that is allowed to mature.
However, if we assume, as Julian Savulescu and Arthur Caplan have said, that this technique is like organ (or micro-organ) donation, then should we be concerned with compatibility issues? While the mitochondrial DNA has its own replication and transcription processes and it codes for some of the proteins used in mitochondrial processes, it does not code for all of them. Many of the genes necessary to code for proteins used in the mitochondria are made from the nuclear DNA. The proteins are transported from the nucleus to the mitochondria through the cytosol. The assumption is that this interaction will be compatible even though the nucleus and the mitochondria have DNA from different people.
Healthy primate offspring have been born from this technique, so this assumptions not unfounded, but, particularly in cases of reproductive technologies, there is a conceptual and biological leap when going from animal models to human subjects. This technique has, apparently, been done in human embryos that have not been implanted in a womb, but there is a limit to what can be discerned from the laboratory setting because human embryological development is a complex process from beginning to end. We must assume that the nucleus and the other organelles are compatible, but we will not actually know until the embryo is implanted development continues.