What importance do donors and recipients attribute to the nuclear DNA-related genetic heritage of oocyte donation?

STUDY QUESTION

How do oocyte donors and recipients perceive the genetic link related to the transfer of nuclear DNA between donors and offspring?

SUMMARY ANSWER

Whether they are donors or recipients, individuals attach great importance to the transmission of their genetic heritage, since 94.5% would opt for the pronuclear transfer method to preserve this genetic link in the context of oocyte donation.

WHAT IS KNOWN ALREADY

Since 1983, the use of oocyte donation has increased worldwide. Performed in France since the late 1980s and initially offered to women with premature ovarian insufficiency, its indications have progressively expanded and now it is proposed in many indications to prevent the transmission of genetically inherited diseases. This has resulted in an increase in the waiting time for access to oocyte donation due to the difficulty in recruiting oocyte donors in French ART centres. Several articles have discussed how to fairly distribute donor oocytes to couples, but few have interviewed women in the general population to record their feelings about oocyte donation, as either the donor or recipient and the importance given to the genetic link between the oocyte donors and the children born. Mitochondrial replacement therapy (MRT) is a technique originally developed for women at risk of transmitting a mitochondrial DNA mutation. Recently, MRT has been considered for embryo arrest and oocyte rejuvenation as it could help females to reproduce with their own genetic material through the transfer of their oocyte nucleus into a healthy donor oocyte cytoplasm.

STUDY DESIGN, SIZE, DURATION

We conducted an opinion survey from January 2021 to December 2021, during which 1956 women completed the questionnaire. Thirteen participants were excluded from the analysis due to incomplete responses to all the questions. Consequently, 1943 women were included in the study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We specifically developed a questionnaire for this study, which was created and distributed using the Drag'n Survey® software. The questionnaire consisted of 21 items presented alongside a video created with whiteboard animation software. The aim was to analyse whether certain factors, such as age, education level, marital status, number of children, use of ART for pregnancy, video viewing, and knowledge about oocyte donation, were associated with feelings towards oocyte donation, by using a univariate conditional logistic regression model. This statistical method was also used to assess whether women would be more inclined to consider oocyte donation with the pronuclear transfer technique rather than the whole oocyte donation. All parameters found to be statistically significant in the univariate analysis were subsequently tested in a multivariate model using logistic regression.

MAIN RESULTS AND THE ROLE OF CHANCE

Most women were concerned about the biological genetic contribution of the donated oocyte (94.8%). The most common reason for a women's reluctance to donate their oocytes was their unwillingness to pass on their genetic material (33.3%). Nearly 70% of women who were initially hesitant to donate their oocytes indicated that they would reconsider their decision if the oocyte donation was conducted using donated cytoplasm and the pronuclear transfer technique. Concomitantly, >75% of the respondents mentioned that it would be easier to receive a cytoplasm donation. The largest proportion of the population surveyed (94.5%) expressed their support for its legalization.

LIMITATIONS, REASONS FOR CAUTION

In this study, a substantial portion of the responses came from individuals with medical or paramedical backgrounds, potentially introducing a recruitment bias among potential donors. The rate of missing responses to the question regarding the desire to become an oocyte donor was 13.6%, while the question about becoming an oocyte cytoplasm donor had a missing response rate of 23%. These missing responses may introduce a bias in the interpretation of the data.

WIDER IMPLICATIONS OF THE FINDINGS

This study was the first to demonstrate that, for the French population studied, the combination of oocyte cytoplasm donation with pronuclear transfer could offer a promising approach to enhance the acceptance of oocyte donation for both the donor and the recipient.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was used for this study. The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

The fragility of origin essentialism: Where mitochondrial 'replacement' meets the non-identity problem

Few discussions of the ethics of mitochondrial 'replacement' techniques have drawn significant ethical distinctions between the two approaches now legal in the U.K. However, Anthony Wrigley, Stephen Wilkinson and John Appleby have together argued that under some circumstances pronuclear transfer (PNT) may be in better ethical standing than maternal spindle transfer (MST). They base their conclusion on what they allege to be different implications of the techniques with respect to non-identity considerations, which they ground on a version of origin essentialism. I raise a series of problems for their argument, which have cautionary implications for invocations of origin essentialism that go beyond specialized debates regarding MST and PNT. I argue that (i) origin essentialism is a fragile foundation for non-identity considerations; (ii) gametic essentialism, which Wrigley et al. believe licenses their claims, is more questionable than origin essentialism; (iii) gametic essentialism does not straightforwardly justify their conclusion; and (iv) their conclusion in fact relies on an especially dubious position that we can call chromosomal origin essentialism. No good reasons have yet been supplied to distinguish PNT from MST on ethical grounds, and one should be wary of basing claims with practical impact on fragile foundations relating to origin essentialism.

Germline nuclear transfer in mice may rescue poor embryo development associated with advanced maternal age and early embryo arrest

STUDY QUESTION

Can pronuclear transfer (PNT) or maternal spindle transfer (ST) be applied to overcome poor embryo development associated with advanced maternal age or early embryo arrest in a mouse model?

SUMMARY ANSWER

Both PNT and ST may have the potential to restore embryonic developmental potential in a mouse model of reproductive ageing and embryonic developmental arrest.

WHAT IS KNOWN ALREADY

Germline nuclear transfer (NT) techniques, such as PNT and ST, are currently being applied in humans to prevent the transmission of mitochondrial diseases. Yet, there is also growing interest in the translational use of NT for treating infertility and improving IVF outcomes. Nevertheless, direct scientific evidence to support such applications is currently lacking. Moreover, it remains unclear which infertility indications may benefit from these novel assisted reproductive technologies.

STUDY DESIGN, SIZE, DURATION

We applied two mouse models to investigate the potential of germline NT for overcoming infertility. Firstly, we used a model of female reproductive ageing (B6D2F1 mice, n = 155), with ages ranging from 6 to 8 weeks (young), 56 (aged) to 70 weeks (very-aged), corresponding to a maternal age of <30, ∼36 and ∼45 years in humans, respectively. Secondly, we used NZB/OlaHsd female mice (7-14 weeks, n = 107), as a model of early embryo arrest. This mouse strain exhibits a high degree of two-cell block. Metaphase II (MII) oocytes and zygotes were retrieved following superovulation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovarian reserve was assessed by histological analysis in the reproductive-aged mice. Mitochondrial membrane potential (△Ψm) was measured by JC-1 staining in MII oocytes, while spindle-chromosomal morphology was examined by confocal microscopy. Reciprocal ST and PNT were performed by transferring the meiotic spindle or pronuclei (PN) from unfertilised or fertilised oocytes (after ICSI) to enucleated oocytes or zygotes between aged or very-aged and young mice. Similarly, NT was also conducted between NZB/OlaHsd (embryo arrest) and B6D2F1 (non-arrest control) mice. Finally, the effect of cytoplasmic transfer (CT) was examined by injecting a small volume (∼5%) of cytoplasm from the oocytes/zygotes of young (B6D2F1) mice to the oocytes/zygotes of aged or very-aged mice or embryo-arrest mice. Overall, embryonic developmental rates of the reconstituted PNT (n = 572), ST (n = 633) and CT (n = 336) embryos were assessed to evaluate the efficiency of these techniques. Finally, chromosomal profiles of individual NT-generated blastocysts were evaluated using next generation sequencing.

MAIN RESULTS AND THE ROLE OF CHANCE

Compared to young mice, the ovarian reserve in aged and very-aged mice was severely diminished, reflected by a lower number of ovarian follicles and a reduced number of ovulated oocytes (P < 0.001). Furthermore, we reveal that the average △Ψm in both aged and very-aged mouse oocytes was significantly reduced compared to young mouse oocytes (P < 0.001). In contrast, the average △Ψm in ST-reconstructed oocytes (very-aged spindle and young cytoplast) was improved in comparison to very-aged mouse oocytes (P < 0.001). In addition, MII oocytes from aged and very-aged mice exhibited a higher rate of abnormalities in spindle assembly (P < 0.05), and significantly lower fertilisation (60.7% and 45.3%) and blastocyst formation rates (51.4% and 38.5%) following ICSI compared to young mouse oocytes (89.7% and 87.3%) (P < 0.001). Remarkably, PNT from zygotes obtained from aged or very-aged mice to young counterparts significantly improved blastocyst formation rates (74.6% and 69.2%, respectively) (P < 0.05). Similarly, both fertilisation and blastocyst rates were significantly increased after ST between aged and young mice followed by ICSI (P < 0.05). However, we observed no improvement in embryo development rates when performing ST from very-aged to young mouse oocytes following ICSI (P > 0.05). In the second series of experiments, we primarily confirmed that the majority (61.8%) of in vivo zygotes obtained from NZB/OlaHsd mice displayed two-cell block during in vitro culture, coinciding with a significantly reduced blastocyst formation rate compared to the B6D2F1 mice (13.5% vs. 90.7%; P < 0.001). Notably, following the transfer of PN from the embryo-arrest (NZB/OlaHsd) zygotes to enucleated non-arrest (B6D2F1) counterparts, most reconstructed zygotes developed beyond the two-cell stage, leading to a significantly increased blastocyst formation rate (89.7%) (P < 0.001). Similar findings were obtained after implementing ST between NZB/OlaHsd and B6D2F1 mice, followed by ICSI. Conversely, the use of CT did not improve embryo development in reproductive-age mice nor in the embryo-arrest mouse model (P > 0.05). Surprisingly, chromosomal analysis revealed that euploidy rates in PNT and ST blastocysts generated following the transfer of very-aged PN to young cytoplasts and very-aged spindles to young cytoplasts were comparable to ICSI controls (with young mouse oocytes). A high euploidy rate was also observed in the blastocysts obtained from either PNT or ST between young mice. Conversely, the transfer of young PN and young spindles into very-aged cytoplasts led to a higher rate of chromosomal abnormalities in both PNT and ST blastocysts.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The limited number of blastocysts analysed warrants careful interpretation. Furthermore, our observations should be cautiously extrapolated to humans given the inherent differences between mice and women in regards to various biological processes, including centrosome inheritance. The findings suggest that ST or PNT procedures may be able to avoid aneuploidies generated during embryo development, but they are not likely to correct aneuploidies already present in some aged MII oocytes.

WIDER IMPLICATIONS OF THE FINDINGS

To our knowledge, this is the first study to evaluate the potential of PNT and ST in the context of advanced maternal age and embryonic developmental arrest in a mouse model. Our data suggest that PNT, and to a lesser extent ST, may represent a novel reproductive strategy to restore embryo development for these indications.

STUDY FUNDING/COMPETING INTEREST(S)

M.T. is supported by grants from the China Scholarship Council (CSC) (Grant no. 201506160059) and the Special Research Fund from Ghent University (Bijzonder Onderzoeksfonds, BOF) (Grant no. 01SC2916 and no. 01SC9518). This research is also supported by the FWO-Vlaanderen (Flemish fund for scientific research, Grant no. G051017N, G051516N and G1507816N). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Genome Modifying Reproductive Procedures and their Effects on Numerical Identity

The advantages and risks of a number of new genome modifying procedures seeking to create healthy or enhanced individuals, such as Maternal Spindle Transfer, Pronuclear Transfer, Cytoplasmic Transfer and Genome Editing, are currently being assessed from an ethical perspective, by national and international policy organizations. One important aspect being examined concerns the effects of these procedures on different kinds of identity. In other words, whether or not a procedure only modifies the qualities or properties of an existing human being, meaning that merely the qualitative identity of this single individual is affected, or whether a procedure results in the creation of a new individual, meaning that a numerically distinct human being would have come into existence. In this article, the different identity arguments proposed, so far, are presented with respect to these novel reproductive procedures. An alternative view is then developed using the Origin Essentialism argument to indicate that any change in the creative conditions of an individual such as in his or her biology but also the moment in time, and the three dimensions of space, will have a numerical identity effect and bring into existence a new individual who would not, otherwise, have existed. Because of this, it is concluded that a form of selection may have taken place in which a preference was expressed for one new possible individual instead of another, based on some frame of reference. This may then mean that a selection between persons has occured  contravening the European Union Charter of Fundamental Rights which was ratified in 2000.

Scientific and Ethical Issues in Mitochondrial Donation

The development of any novel reproductive technology involving manipulation of human embryos is almost inevitably going to be controversial and evoke sincerely held, but diametrically opposing views. The plethora of scientific, ethical and legal issues that surround the clinical use of such techniques fuels this divergence of opinion. During the policy change that was required to allow the use of mitochondrial donation in the UK, many of these issues were intensely scrutinised by a variety of people and in multiple contexts. This extensive process resulted in the publication of several reports that informed the recommendations made to government. We have been intrinsically involved in the development of mitochondrial donation, from refining the basic technique for use in human embryos through to clinical service delivery, and have taken the opportunity in this article to offer our own perspective on the issues it raises.

Preventing Mitochondrial Diseases: Embryo-Sparing Donor-Independent Options

Mutant mitochondrial DNA gives rise to a broad range of incurable inborn maladies. Prevention may now be possible by replacing the mutation-carrying mitochondria of zygotes or oocytes at risk with donated unaffected counterparts. However, mitochondrial replacement therapy is being held back by theological, ethical, and safety concerns over the loss of human zygotes and the involvement of a donor. These concerns make it plain that the identification, validation, and regulatory adjudication of novel embryo-sparing donor-independent technologies remains a pressing imperative. This Opinion highlights three emerging embryo-sparing donor-independent options that stand to markedly allay theological, ethical, and safety concerns raised by mitochondrial replacement therapy.

Kinship Identities in the Context of UK Maternal Spindle Transfer and Pronuclear Transfer Legislation

In the discussions leading up to the enactment of the UK Human Fertilisation and Embryology (Mitochondrial Donation) Regulations 2015, it was repeatedly emphasised, by many commentators, that maternal spindle transfer (MST) and pronuclear transfer (PNT) did not give rise to children who could be considered as having three or more parents. This was because it was argued that only the genetic material found in the chromosomes should be considered as the determining factor for the formation of parent-child relationships and the resulting kinship identities. In this present study, however, this assertion will be questioned in the light of different kinds and different understandings of kinship identities. It will also be suggested that any person who is partly responsible for the very existence of a child, through any means, may qualify as a causal parent - a parent whom the resulting child may want to identify. As a result, a positive response should be given to a request from a person born from MST and PNT concerning identifying information for all the individuals responsible for bringing him or her into existence. In the light of this, the article will conclude that it is regrettable that the UK government enacted binding legislation making sure that children, born through MST and PNT, will never be able to contact the egg donors and, in the case of PNT, the sperm donors. This reflects a very limited understanding of who parents really are and may give rise to serious long-term psychological distress in the prospective children.

Mitochondrial replacement techniques and Mexico's rule of law: on the legality of the first maternal spindle transfer case

News about the first baby born after a mitochondrial replacement technique (MRT; specifically maternal spindle transfer) broke on September 27, 2016 and, in a matter of hours, went global. Of special interest was the fact that the mitochondrial replacement procedure happened in Mexico. One of the scientists behind this world first was quoted as having said that he and his team went to Mexico to carry out the procedure because, in Mexico, there are no rules. In this paper, we explore Mexico's rule of law in relation to mitochondrial replacement techniques and show that, in fact, certain instances of MRTs are prohibited at the federal level and others are prohibited at the state level. According to our interpretation of the law, the scientists behind this first successful MRT procedure broke federal regulations regarding assisted fertilization research.

Mitochondrial Modification Techniques and Ethical Issues

Current strategies for preventing the transmission of mitochondrial disease to offspring include techniques known as mitochondrial replacement and mitochondrial gene editing. This technology has already been applied in humans on several occasions, and the first baby with donor mitochondria has already been born. However, these techniques raise several ethical concerns, among which is the fact that they entail genetic modification of the germline, as well as presenting safety problems in relation to a possible mismatch between the nuclear and mitochondrial DNA, maternal mitochondrial DNA carryover, and the "reversion" phenomenon. In this essay, we discuss these questions, highlighting the advantages of some techniques over others from an ethical point of view, and we conclude that none of these are ready to be safely applied in humans.

Ethics of Mitochondrial Replacement Techniques: A Habermasian Perspective

Jürgen Habermas is regarded as a central bioconservative commentator in the debate on the ethics of human prenatal genetic manipulations. While his main work on this topic, The Future of Human Nature, has been widely examined in regard to his position on prenatal genetic enhancement, his arguments regarding prenatal genetic therapeutic interventions have for the most part been overlooked. In this work I do two things. First, I present the three necessary conditions that Habermas establishes for a prenatal genetic manipulation to be regarded as morally permissible. Second, I examine if mitochondrial replacement techniques meet these necessary conditions. I investigate, specifically, the moral permissibility of employing pronuclear transfer and maternal spindle transfer. I conclude that, according to a Habermasian perspective on prenatal genetic manipulation, maternal spindle transfer (without using a preselected sperm and egg) and pronuclear transfer are morally impermissible. Maternal spindle transfer is, in principle, morally permissible, but only when we have beforehand preselected a sperm and an egg for our reproductive purpose. These findings are relevant for bioconservatives, both for those who hold a Habermasian stance and for those who hold something akin to a Habermasian stance, because they answer the question: what should bioconservatives do regarding mitochondrial replacement techniques? In fact, the answer to this question does not only normatively prescribe what bioconservatives should do in terms of their personal morality, but it also points towards what kind of legislation regulating mitochondrial replacement techniques they should aim at.

Weigh and wait: the prospect of mitochondrial gene replacement

Mitochondrial DNA transfer has recently received attention from physicians. The transfer techniques place genetic material from the egg nucleus of a woman with a mitochondrial DNA mutation into a healthy donated egg from which the nuclear DNA was removed. This technology intends to reconstruct a mitochondria-competent egg to produce a baby. Three approaches: (1) pronuclear transfer; (2) metaphase II spindle transfer (ST); and (3) polar body (PB) transfer, have been proposed and applied in animal models with very low levels of heteroplasmy. Because there is no curative treatment for patients with mitochondrial dysfunction, the UK government has allowed the use of this pioneering technique to prevent the transmission of rare and devastating mitochondrial diseases. Despite general safety in the observation period, this technology involves germline modification, raising scientific and ethical questions in the public. In this review, we focus on this unprecedented technology and discuss its clinical application in the future.

Pregnancy derived from human zygote pronuclear transfer in a patient who had arrested embryos after IVF

Nuclear transfer of an oocyte into the cytoplasm of another enucleated oocyte has shown that embryogenesis and implantation are influenced by cytoplasmic factors. We report a case of a 30-year-old nulligravida woman who had two failed IVF cycles characterized by all her embryos arresting at the two-cell stage and ultimately had pronuclear transfer using donor oocytes. After her third IVF cycle, eight out of 12 patient oocytes and 12 out of 15 donor oocytes were fertilized. The patient's pronuclei were transferred subzonally into an enucleated donor cytoplasm resulting in seven reconstructed zygotes. Five viable reconstructed embryos were transferred into the patient's uterus resulting in a triplet pregnancy with fetal heartbeats, normal karyotypes and nuclear genetic fingerprinting matching the mother's genetic fingerprinting. Fetal mitochondrial DNA profiles were identical to those from donor cytoplasm with no detection of patient's mitochondrial DNA. This report suggests that a potentially viable pregnancy with normal karyotype can be achieved through pronuclear transfer. Ongoing work to establish the efficacy and safety of pronuclear transfer will result in its use as an aid for human reproduction.