Bioethics Blogs

“3-Parent Babies”—Half-Speed Ahead?

Three weeks ago, the Institute of Medicine released its FDA-requested report “Mitochondrial Replacement Techniques: Ethical, Social, and Policy Considerations.”  The report may be read online, or a prepublication pdf copy may be downloaded for free, at this link.

In view is the so-called “3-parent babies” technology, intended to treat inherited diseases of the mitochondria, components (called “organelles”) of a cell that are responsible for producing the energy needed for life.  These diseases are rare, but devastating when they occur.  There are actually genes in our mitochondria—37, to be exact, compared with 20-30,000 in the nuclei of our cells.  Those 20-30,000 are the genes that “make you you,” as they say.  The 37 in the mitochondria are ones we don’t notice unless they are messed up—kind of like you view your car’s engine on most days, I bet.  Mitochondrial diseases are inherited from mom, not dad, because sperm lose their mitochondria when they are formed.

To fashion treatment, there are two main options.  One is to take an affected fertilized egg, remove its nucleus, and insert said nucleus into a second, normal fertilized egg that has had its nucleus removed.  The result is a new fertilized egg—the earliest stage of an embryo—that has the genetic material from the diseased mom, but healthy mitochondria from the normal fertilized egg—that is, embryo—which has been “donated” for the purpose.  Both of the original embryos are destroyed in the process; the new one is at least mostly new.  The second approach, considered less promising, is to try to do this process between two eggs before fertilization: one normal (donated) and one diseased (which has the genes from the mom, for her intended baby—healthy, it is hoped).  The nucleus (and its genes) are removed from the diseased mom’s egg and placed into the donor egg, which has had its nucleus removed.  The resulting new egg is then fertilized, implanted into mom’s uterus, and from there one hopes things proceed smoothly.  This has been done successfully in animals, and the resulting offspring at least appear normal.  (Longer-term results, including outcomes for subsequent animal generations, are still to be determined.)  Whether it all would work in people remains to be seen, not just at birth or in childhood, but throughout the offspring’s life and potentially extending into subsequent generations.  We don’t know how they will do, and we wouldn’t for some time now. 

The IOM committee addressed whether, and under what conditions, it is ethically permissible to try this to give an affected mom a chance at healthy offspring.  The report is detailed and thorough.  I cannot cover its recommendations, or the ethical issues, in a single blog post.  Other contributors and I have written about this on this blog during the last two years.  

If one holds that human lives warrant protection from the point of fertilization, then the pronuclear transfer between embryos, at least, is out of bounds.  If one, like the committee, does not hold that, then emphasis is placed on the many other ethical concerns.

The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.