Is It Possible for a Child to Have Three Parents?
Medical advancements have recently created offspring with more than two parents. The ethical nature of these procedures are still debated. Perhaps if there are natural examples of triparental offspring, the ethical issues would be easier to resolve.
Medically Created Triparental Offspring
For a number of reasons, procedures that result in an offspring with more than two biological parents have been developed. On a relatively basic level, artificial insemination and surrogacy result in an offspring with two genetic parents, but with a third parent as the mother carrying the child.
In more extreme cases, it is possible for a child to be created with three genetic parents. This process has been used to prevent genetic disorders involving the mitochondria of the mother. While most people think of genes being limited to the DNA in our own nuclei, mitochondria, in humans, have their own separate DNA. The mitochondria of the mother, and thus any genetic issues with those mitochondria, are passed from mother to offspring, via the egg.
There are a few ways to deal with this issue. One procedure has that has recently been used to prevent a mitochondrial disorder, is a process that is very similar to cloning. The process starts by collecting a healthy egg from a donor. The nucleus of that egg is removed. Then the nucleus from one of the mother’s eggs is extracted and implanted into the donor egg. Finally, the new hybrid egg is fertilized with the father’s sperm. At this point the nuclear DNA consists of the two biological parents, but the mitochondria, and thus the mitochondrial DNA, comes from the donor.
A reported world-first in fertility therapy - a baby boy conceived using a controversial technique that mixes DNA from…www.nature.com
A number of ethical issues have been proposed for triparental offspring. The major issue is that the methods are still fairly untested. It’s rare that there’s a need for this procedure, and it is unethical to create human embryos just to test a medical procedure.
Another issue is that these types of procedures can lead to designer babies. Congress has banned most genetic manipulation of embryos, but it’s still unclear whether the ban includes these types of medical procedures. The procedure is generally deemed acceptable, under the restriction that the reason for the procedure is purely medical.
A final ethical consideration is that of parental rights. Given that the offspring has the DNA of three parents, some argue that the views of the third parent should be considered.
Because the genetic contribution from the mitochondrial DNA donor is essential and critical for the development of a healthy child, and because emerging studies show that several mitochondrial genes affect mental illness, we argue that the genetic contribution from mtDNA should not be considered irrelevant to the status of parenthood.
© JENNY NICHOLS, WELLCOME IMAGES In 2015, the US Congress banned the use of gene-editing techniques, such as CRISPR…www.the-scientist.com
Natural Triparental Offspring
If there were humans that naturally exited with more than two parents, the it might be deemed far more ethically reasonable to create offspring with three parents, through medical interventions.
While it is rare, it is possible for eggs to be fertilized by two different instances of sex. This condition is called superfecundation. Likewise, it is possible for those two events to be by different fathers: heteropaternal superfecundation (HS).
It is also possible for a person to actually have cells from two different individuals. It’s called chimerism. The form of chimerism that occurs in humans is called tetragametic chimerism. The condition is more common than once thought, and has been an issue in a number of legal disputes, including parental disputes.
It may be possible, under the right conditions, for both heteropaternal superfecundation and tetragametic chimerism to occur. In such an instance, an individual organism would be composed of cells from two different individuals, each having a separate father.
Assuming that the developing embryo doesn’t fail to thrive, given the two distinct cell lines conflicting with each other, the embryo would continue to develop, with two different cell lines, from two different fathers, and you would end up with a single offspring with three parents.
However, it would likely be extremely rare. Any estimate for how rare it might be would be a wild guess. But since this is a research rabbit hole article, I might as well give it a shot. There are a number of factors to consider. The first is how often HS occurs.
Some research indicates that it might be as high as 2.4% of digyzotic (DZ) twins. The source for this figure is old, but this article is just an attempt to create a very rough guestimate.
Chimerism has traditionally been seen as being a very rare phenomenon. But this view seems to be incorrect. According to newer analyses, almost 10% of liveborn DZ twins exhibit chimerism. This rate is estimated to be greater than 20% in DZ triplets.
Human spontaneous chimerism, with one body built from cells of both twins of a dizygotic (DZ) pair, is supposed to be…academic.oup.com
The rate of DZ twinning is complicated by its variable nature. Apparently factors such as ethnicity, age, whether the mother is a twin, etc all impact the rate of DZ twinning.
The tendency to conceive spontaneous dizygotic (DZ) twins is a complex trait with important contributions from both…academic.oup.com
MZ twinning seems to occur at roughly 4 per 1,000 maternities. With a total average rate of twinning of 13 per 1,000 this means that rate of DZ twinning averages 9 per 1,000. I’m not sure if this figure includes DZ triplets and above, but I’ll assume that it does, since I’m looking for a low ball figure anyway. Finally, according to the WHO, each year there are roughly 123 million intentional pregnancies with an additional 87 million unintentional pregnancies.
So on average, there are roughly 1.89 million DZ twinnings. If 2.4% are HS twinnings, then there are ~45,000 HS twins. If 10% of those twins end up as chimera, then that’s roughly 4,500 HS chimera. Honestly, this figure seems a little high still, but even if it’s only 1% of that figure, then that’s still 45 per year, worldwide. Again, these are all just guestimates. It would take a lot more thought to really figure out if this figure makes any sense at all. But it’s an interesting thought.
While the existence of naturally occurring triparental individuals may be extremely rare, if any are found, the ethical nature of medically created individuals with three parents becomes far less of a challenge. If the condition is not as rare as I’m estimating, and we become aware of the existence of such individuals, the law will have to deal with biological triparental rights anyway. Moreover, medical science would not be creating a new phenomenon, even if the specific way in which the three parents contribute to the offspring differ.