Mitochondrial DNA in Halakhah
Media was abuzz this week with the news of the successful birth of child conceived via mitochondrial transfer. ‘Standard’ IVF mixes sperm with an egg to create a zygote (the reality of far more complex). Just like the DNA of a ‘naturally’ conceived child, an IVF baby’s DNA is a similar compliment of maternal and paternal DNA.
But even while generally accurate about both ‘natural’ and IVF conceived embryos, it’s not exactly so. When we refer to an embryo’s DNA consisting of half maternal and half paternal components, we are referring to the nuclear DNA. The DNA that is responsible for making us who we are and that determines everything about us. Just about everything.
Mitochondrial DNA
For cells to function, they must generate their own energy through cytoplasmic organelles known as mitochondria. These mitochondria contain there own, far smaller and simpler DNA (referred to as mtDNA) that controls and determines mitochondrial function. Interestingly, these are exclusively inherited from the egg donor, since during fertilization, the sperm only contributes nuclear DNA while the egg provides all of the ‘background’ cellular apparatus, including the mitochondria. What this means is that every child essentially inherits all of his or her mitochondria and mtDNA from their mother. If the mother (egg donor) happens to suffer from one of the rare mitochondrial diseases, all of her children are virtually guaranteed to inherit the disease as well.
Mitochondrial transfer is a technology that allows removing the nucleus from a newly formed embryo (formed by the egg and sperm donors’ DNA) and placing that nucleus into another woman’s enucleated egg. This way, the overwhelming majority of the ensuing child’s DNA will be from his or her parents (egg and sperm donors) even while their mtDNA will be from a third party.
What if any effect does this have on establishing halakhic maternity?
Poskim of the previous generation debated the issue with regard to gestational surrogates — does Halakhah recognize the birth mother or the genetic mother as the halakhic mother of the child? Over the past several years, the halakhic consensus has come down on the side of recognizing the genetic mother as halakhically relevant. That said, some Poskim advocate performing a geirut le-humra (conversion as a stringency) as the ramifications are of such significance that it’s desirous to ensure that there will never be any questions as to the child’s status. Taking this position as dispositive, what happens when their is a third genetic partner in the form of mtDNA?
Halakhic Debate
After first establishing that there is scant little halakhic precedent to analyze this issue, Rav Asher Weiss (unpublished responsum) argues that halakhic maternity should follow the nuclear DNA donor — the egg from which the overwhelming majority of traits, features, and characteristics derive.
אך מ”מ נראה דבני”ד כאשר רובו העצום של החומר התורשתי מצוי בגרעין הביצית של האם היהודייה ורק כאלפית ממנו מצוי בחלק הלקוח מן התורמת הנכרייה ודאי מסתבר דאזלינן בתר הרוב והעיקר והולד ישראל לכל דבר, ואם אביו כהן הוא כך דין הולד.
He writes that considering that there can only be one mother — we are left with having to choose between these two women.
אך באמת עיקר חילי ממה דנראה בעיני ברור ופשוט דלא יתכן כלל מבחינת ההלכה שיהיו לאדם שתי אמהות כשם שא”א שיהיו לו שני אבות, ואי דהאי לאו דהאי, וא”כ בהכרח צריך להכריע בין זו לזו, ומשו”כ נראה פשוט דצריך לילך אחר העיקר שבעיקרים ולהתעלם מן הטפל שבטפלים.
And although this case is not completely parallel to other Talmudic discussions, Rav Weiss argues that the principles of rov and miut (majority and minority) should apply. He explicitly acknowledges the shortcomings that mtDNA presents a situation that is different that classic cases of mixtures where rov and miut are operative, but argues that nonetheless, when looking to the Talmud for guidelines, rov and miut seem the most appropriate and applicable in this situation.
אך בהכרח עלינו להשתדל ולהתאמץ ביושר הסברא להבין דבר מתוך דבר. והנה כלל גדול בכל מקום כאשר יש סתירה בין רוב ומיעוט הרוב מכריע את המיעוט, כך הלכה בתערובת איסור והיתר, בסכך כשר ופסול וכך בהלכות רבות וכדילפינן מסנהדרין דכתיב ביה אחרי רבים להטות, וכעי”ז אמרו עוד (נזיר מ”ב ע”א) רובו ככולו … וכך מסתבר גם בני”ד, דיש להכריע דהאם שכמעט כל החומר הגנטי מעצמה ובשרה היא האם עפ”י ההלכה והולד מתייחס אחריה.
Rabbi J. David Bleich disagrees (reprinted in Contemporary Halakhic Problems, vol. 7). He challenges the notion that Rav Asher Weiss takes for granted that a person can only have one father and one mother and finds proof for this in a comment of Tosafot to Sotah 42b. In the context of decrying the personality and irreverence of Goliat (Goliath), the Talmud describes the promiscuity of his mother, with a somewhat cryptic comment (בר מאה פפי וחדא נאנאי). Rashi explains that it means that she was with 100 men one night and therefore could not know with certainty who was Goliat’s real father. Tosafot quotes a Yerushalmi (Yevamot ch. 4) which quote the Rabbanan De-Aggadeta (rabbis of the ‘parables’) who seem to argue that all of these men were Goliat’s father as they all contributed toward his conception. While there is no known biological mechanism through which this would be plausible, that is not the point. Rabbi Bleich focuses on the lack of Tosafot’s reaction to the contention. If it were so obvious that a person could only have one father and one mother, then Tosafot should have rejected this idea outright — regardless of biology — as philosophically / religiously untenable. Meaning, regardless of the biological plausibility of the idea, citing this Yerushalmi without argument implies Tosafot’s acceptance of the plurality of paternity. Rabbi Bleich then makes the small jump that just as pluralistic paternity seems to be a valid halakhic construct, there is no reason to discriminate and pluralistic maternity is just as plausible.
He therefore suggests that with regard to mtDNA transfer, there is no reason to a priori ignore the mitochondrial DNA simply because it is smaller in quantity than the nuclear DNA and we therefore must recognize both the nuclear DNA as well as the mitochondrial DNA donors as halakhic mothers. [Interestingly, Rabbi Bleich also holds that a gestational surrogate also counts as a halakhic mother (embracing and expanding the notion of pluralistic maternity) which could then mean that a child could conceivably have three different mothers.] With further advances in DNA technology, it is not unreasonable to envision a time when various sections of nuclear DNA might be spliced in from other donors, thereby potentially expanding the possibilities for an even greater number of parents.
Understanding the Debate
These Poskim seem to be implicitly arguing about the inherent nature of what it means to be a parent. For Rav Asher Weiss, Halakhah recognizes one mother and one father for each person — letting the biology fall as it may. When presented with multiple biological contributors, some decision needs to be made as to how to assign those roles. Rabbi Bleich however, understand that Halakhah assigns parentage to all contributors of genetic material to an embryo regardless of the number. Indeed, there should be no reason to limit it to genetic donors as the same argument could be made for cytoplasmic donors or contributors of other, genetic-less organelles. (This would fit in well with Rabbi Bleich’s previously articulated view of how heredity is generally determined XXXXX).
Interestingly, the Arukh (s.v. ben [4]) adds an interesting twist to the sordid tale by noting that in addition to the 100 men, Goliat’s mother also committed bestiality with a dog. The Ben Ish Chai (Ben Yehoyada, Sotah ibid.) elaborates that this is why Goliat responds so harshly to David when he saw him approach with a slingshot, “Am I a dog that you come against me with sticks?” (Shmuel I 17:43). What he means, Ben Ish Chai explains, was that even if David had heard that one of Goliat’s “fathers” was a dog, he in fact (meaning Goliat) is a full fledged person [from which David should be frightened]. Considering that it was only one contribution to his conception out of 100, it has no bearing on his actual makeup [and perhaps even heritage]. Effectively, Ben Ish Chai is willing to accept the idea that an embryo could have multiple potential fathers, but nonetheless, some seem to be more important than others and not counting as sufficiently important toward determining the nature of the ensuing progeny.
While not completely parallel to the various contributions of nuclear DNA vs. mtDNA it at least establishes a precedent for assigning priority to some genetic contributors over others (at least in Tosafot‘s and the Yerushalmi’s biological worldview), leaving room for not necessarily considering each and every genetic contributor to be considered a halakhic parent.
What About the Future?
Keeping all of this in mind, it’s fascinating to explore how Halakhah will view a cloned person. One method of cloning involves taking a fully developed somatic cell, removing its nucleus, and placing it into a previously enucleated egg cell. This egg cell would now have a full complement of 46 chromosomes and would be stimulated in some way to reproduce. Who are this child’s parents?
The nuclear DNA and the egg could potentially come from the same woman or from a different man or woman? If a man contributed all of the nuclear DNA, would Rav Asher Weiss still dismiss the female mtDNA donor as a halakhic mother, thereby leaving this child with no mother? If various cellular components came from different people or were possibly even artificially manufactured, would Rabbi Bleich consider all to be potential halakhic parents?
To be continued …