The technique that the United States and, more seriously, the United Kingdom are considering bringing to the IVF clinic, which creates embryos with three genetic parents, is often “mitochondrial replacement” or “mitochondrial transfer.”
Why that terminology? Well the point of this genetic engineering of children is to “replace” defective mitochondria, little organelles in our cells that produce energy. Mitochondria have their own DNA (mtDNA) and we inherit our mtDNA from our mother exclusively since they are present in her egg when we are conceived. Women with mutations in their mtDNA will pass those on to her children.
So “mitochondrial replacement” or “mitochondrial transfer” seem like appropriate terms to use to describe the three-parent embryo technique. Actually, they are horribly deceptive as Dr. Stuart A. Newman, professor of Cell Biology and Anatomy at New York Medical College, rightly points out in the Huffington Post.
Looking closer at the technique one realizes that “mitochondrial replacement” (MR) doesn’t actually replace mitochondria. What happens is this: an egg from a donor has its nucleus removed leaving healthy mitochondria behind. Then the nucleus from an egg of a woman with mitochondral disease is placed in that donor egg. What results is an egg that has had its NUCLEUS replaced, not its mitochondria.
That genetically engineered egg is then fertilized with sperm, and an embryo with the genetic material from three people is then made. Dr. Newman calls it “the first cases of large-scale human genetic engineering” and he is right.
So why call what is a really a nucleus replacement a mitochondrial replacement? Probably because the public is more likely to support the practice. Dr. Newman calls this misnomer “deceptive” because it is like buying a new house and calling it a “refrigerator replacement.”
Because MR replaces the nucleus, not the mitochondria, it is actually more like cloning than anything else. Dr. Newman calls MR techniques by their proper names, maternal spindle transfer (MST) and pronuclear transfer (PNT) and explains why these techniques are a lot like cloning:
In biological terms, both MST and PNT are very much like cloning by nuclear transfer, the methodology that produced Dolly the sheep. Like cloning, the techniques involve replacement of an egg’s nucleus by a nucleus from another cell. When cloning, the transferred nucleus is from a differentiated cell of a fully developed animal (or potentially, a person), making the resulting organism a genetic “copy” of the nucleus donor. When undertaking MST and PNT, the transferred nucleus is from an egg or a fertilized egg, so that the resulting organism will have a novel genome. Otherwise, however, the hazards of cloning also pertain to MST and PNT, since the manipulations are the same. Clones tend to die prematurely, as happened with Dolly, or exhibit enlarged organs and metabolic abnormalities. Some human embryos constructed by MST unexpectedly had unbalanced chromosomal duplications (aneuploidy). This is the case because unlike the sorts of cellular aberrations repeatedly encountered over the course of evolution – breaks in DNA, the unfolding of protein molecules – the experimental combination of fragments of two broken cells generated by cloning or the two proposed techniques have no inbuilt mechanisms to correct the range of functional and developmental defects inevitably associated with their construction.
So essentially, if mitochondrial replacement moves forward it will bring with it all the risks associated with cloning.
Dr. Newman also points out that the 37 genes of mtDNA has a much greater affect on the human person than previously thought:
Moreover, anyone familiar with the relevant science would have been aware, over the period during which the techniques were being evaluated by the British Human Fertilisation & Embryology Authority (HFEA) and the U.S. Food and Drug Administration (FDA), of evidence that mitochondria are not (as the impact-minimizing refrain has it) mere energy-providing organelles. The very existence of mitochondrial DNA mutations affecting hearing, vision, pancreatic function and neuromuscular activity (the justifications of the entire enterprise), would be enough to tell us this. Indeed, in the past two years the evidence for the non-passivity of the mitochondria has become inescapable. Since mitochondria are active participants in cell function and organismal development, integration among coevolved nuclear and mitochondrial systems would contraindicate arbitrary mixing and matching. (The engines of a Jaguar and a Rolls-Royce do essentially the same thing, but they are not interchangeable.) This adds an array of hazards to MST and PNT that go well beyond those they share with cloning.
In other words, just because you can put the engine of one high performance car into another, does not mean that doing so will making a perfectly functioning automobile. It is highly likely things will go wrong. Dr. Paul Knoepfler, associate professor of Cell Biology and Human Anatomy at UC Davis, agrees.
And because this is a germ-line modification, anything that does go wrong may be passed onto future generations.
How can we possibly even consider this? Does the safety of the next generation, and every generation after, even register with the proponents of MR?
I truly believe we are at a critical point in human history. Will we allow this reckless experimentation on future generations without their consent or will we realize that the health and well-being of future generations trumps parental desires?
If we answer “yes” to the former, we will be opening the Pandora’s Box of human germ-line genetic engineering, and I am positive we will not be able to close that box once its opened.