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Mitochondrial replacement therapy (MRT) has been used to prevent maternal transmission of disease-causing mutations in mitochondrial DNA (mtDNA). However, because MRT requires nuclear transfer, it carries the risk of mtDNA carryover and hence of the reversion of mtDNA to pathogenic levels owing to selective replication and genetic drift. Here we show in HeLa cells, mouse embryos and human embryos that mtDNA heteroplasmy can be reduced by pre-labelling the mitochondrial outer membrane of a donor zygote via microinjection with an mRNA coding for a transmembrane peptide fused to an autophagy receptor, to induce the degradation of the labelled mitochondria via forced mitophagy. Forced mitophagy reduced mtDNA carryover in newly reconstructed embryos after MRT, and had negligible effects on the growth curve, reproduction, exercise capacity and other behavioural characteristics of the offspring mice. The induction of forced mitophagy to degrade undesired donor mtDNA may increase the clinical feasibility of MRT and could be extended to other nuclear transfer techniques.

Mitochondrial replacement therapy (MRT), also called nuclear genome transfer and mitochondrial donation, is a new technique that can be used to prevent the transmission of mitochondrial DNA diseases. Apart from the United Kingdom, the first country to approve MRT in 2015, Australia became the second country with a clear regulatory path for the clinical applications of this technique in 2021. The rapidly evolving clinical landscape of MRT makes the elaboration and evaluation of the responsible use of this technology a pressing matter. As jurisdictions with less strict or non-existent reproductive laws are continuing to use MRT in the clinical context, the need to address the underlying ethical issues surrounding MRT’s clinical translation is fundamental.

PURPOSE: During fertilisation, female and male pronuclei (PNs) migrate to the centre of the ooplasm, juxtapose, and break down synchronously in preparation for the first mitosis. While PN non-juxtaposition and PN breakdown (PNBD) asynchrony are occasionally observed, their developmental implications remain uncertain. This study investigated the possible relationships among the two phenomena, preimplantation development patterns, and live birth rates in single blastocyst transfers. METHODS: A total of 1455 fertilised oocytes cultured in a time-lapse incubator were retrospectively analysed. Fertilised oocytes were divided into four groups according to the presence of PN juxtaposition and breakdown synchrony. The relationships of abnormal PN behaviour with embryo morphokinetics, blastocyst formation, and live birth were evaluated. RESULTS: PN non-juxtaposition and asynchrony were observed in 1.9% and 1.0% of fertilised oocytes, respectively. The blastocyst cryopreservation rates in the synchronous–non-juxtaposed and asynchronous–non-juxtaposed groups were significantly lower than that in the synchronous–juxtaposed group. The rates of clinical pregnancy, ongoing pregnancy, and live birth were comparable among the groups. Non-juxtaposition was significantly associated with increased trichotomous cleavage at the first cytokinesis (P < 0.0001) and an increase in the time interval from PNBD to first cleavage (P < 0.0001). Furthermore, asynchronous PNBD was significantly correlated with increased rapid cleavage at the first cytokinesis (P = 0.0100). CONCLUSION: Non-juxtaposition and asynchronous PNBD is associated with abnormal mitosis at the first cleavage and impaired preimplantation development. However, embryos displaying abnormal PNBD may develop to blastocyst stage and produce live births, suggesting blastocyst transfer as a more appropriate culture strategy. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10815-021-02335-6.

As the vital organelles for cell energy metabolism, mitochondria are essential for oocyte maturation, fertilization, and embryo development. Abnormalities in quantity, quality, and function of mitochondria are closely related to poor fertility and disorders, such as decreased ovarian reserve (DOR), premature ovarian aging (POA), and ovarian aging, as well as maternal mitochondrial genetic disease caused by mitochondrial DNA (mtDNA) mutations or deletions. Mitochondria have begun to become a therapeutic target for infertility caused by factors such as poor oocyte quality, oocyte aging, and maternal mitochondrial genetic diseases. Mitochondrial replacement therapy (MRT) has attempted to use heterologous or autologous mitochondria to rebuild healthy state of oocyte by increasing the amount of mitochondria (e.g., partial ooplasm transfer, autologous mitochondrial transfer), or to stop the transmission of mtDNA diseases by replacing abnormal maternal mitochondria (e.g., pronuclei transfer, spindle transfer, polar body transfer). Among them, autologous mitochondrial transfer is the most promising therapeutic technology as of today which does not involve using a third party, but its clinical efficacy is controversial due to many factors such as the aging phenomenon of germ line cells, the authenticity of the existence of ovarian stem cells (OSC), and secondary damage caused by invasive surgery to patients with poor ovarian function. Therefore, the research of optimal autologous cell type that can be applied in autologous mitochondrial transfer is an area worthy of further exploration. Besides, the quality of germ cells can also be probably improved by the use of compounds that enhance mitochondrial activity (e.g., coenzyme Q10, resveratrol, melatonin), or by innovative gene editing technologies which have shown capability in reducing the risk of mtDNA diseases (e.g., CRISPR/Cas9, TALENTs). Though the current evidences from animal and clinical trials are not sufficient, and some solutions of technical problems are still needed, we believe this review will guide a new direction in the possible clinical applied mitochondrial-related therapeutic strategies in reproductive medicine.

Mitochondrial disorders affect at least 1 in 5,000 individuals worldwide and are often incurable and fatal. Mitochondrial replacement therapy (MRT) is an in vitro fertilization technique used to prevent the transmission of mitochondrial disorders. Currently, MRT is the only approach that provides mothers who carry a pathogenic variant in their mitochondrial DNA (mtDNA), the opportunity to have a biological child without a mitochondrial disease. MRT involves the combination of nuclear DNA from the egg of the carrier mother and the cytoplasm from an oocyte donor, which contains healthy mitochondria. While MRT was approved for use in the UK in 2015, the ban on congressional funding for research on 'heritable genetic modification' has made MRT unavailable within the US borders. This survey-based study aimed to describe genetic counselors' experience, knowledge, and opinions about MRT. Additionally, we also assessed whether genetic counselors' comfort discussing MRT with patients, and feelings about clinical use of MRT in the United States changed after providing information about MRT compared with baseline. Responses were received from 139 genetic counselors in North America. Findings indicate low awareness and knowledge about MRT among participants. However, more participants expressed comfort with discussing MRT with patients and more participants were able to form opinions about statements about MRT after they were provided with information about MRT. This study is the first to assess genetic counselors' opinions toward MRT and suggests the need for more education about novel technologies such as MRT among genetic counselors.

Mitochondrial replacement therapy (MRT) in Canada is considered a criminal offense according to article 5(1)(f) of the Assisted Human Reproduction Act (AHRA) (2004). The Act prohibits any practice that modifies the genome of “a human being or in vitro embryo such that the alteration is capable of being transmitted to descendants.” We carried out 32 semi-structured interviews with clinicians, researchers, patient groups, egg donors, and members of the public to explore their attitudes toward the clinical implementation of MRT in Canada. Our interview guide was informed by the socio-ethical, legal, and scientific literature of MRT. We used a thematic analysis to identify and analyze emerging themes and sub-themes. Our findings were divided into five broad themes: ( i) an outdated criminal ban, ( ii) motives for using MRT, ( iii) terminology, ( iv) practical and theoretical risks and benefits, and ( v) the feasibility of clinical translation in Canada. Although the public and stakeholders’ views on the feasibility of foreseeable translation of MRT in Canadian clinics varied, there was consensus on conducting an overdue review of the current AHRA ban on MRT.

STUDY QUESTION What are the long-term developmental, reproductive and genetic consequences of mitochondrial replacement therapy (MRT) in primates? SUMMARY ANSWER Longitudinal investigation of MRT rhesus macaques (Macaca mulatta) generated with donor mtDNA that is exceedingly distant from the original maternal counterpart suggest that their growth, general health and fertility is unremarkable and similar to controls. WHAT IS KNOWN ALREADY Mitochondrial gene mutations contribute to a diverse range of incurable human disorders. MRT via spindle transfer in oocytes was developed and proposed to prevent transmission of pathogenic mtDNA mutations from mothers to children. STUDY DESIGN, SIZE, DURATION The study provides longitudinal studies on general health, fertility as well as transmission and segregation of parental mtDNA haplotypes to various tissues and organs in five adult MRT rhesus macaques and their offspring. PARTICIPANTS/MATERIALS, SETTING, METHODS MRT was achieved by spindle transfer between metaphase II oocytes from genetically divergent rhesus macaque populations. After fertilization of oocytes with sperm, heteroplasmic zygotes contained an unequal mixture of three parental genomes, i.e. donor (≥97%), maternal (≤3%), and paternal (≤0.1%) mitochondrial (mt)DNA. MRT monkeys were grown to adulthood and their development and general health was regularly monitored. Reproductive fitness of male and female MRT macaques was evaluated by time-mated breeding and production of live offspring. The relative contribution of donor, maternal, and paternal mtDNA was measured by whole mitochondrial genome sequencing in all organs and tissues of MRT animals and their offspring. MAIN RESULTS AND THE ROLE OF CHANCE Both male and female MRT rhesus macaques containing unequal mixture of three parental genomes, i.e. donor (≥97%), maternal (≤3%), and paternal (≤0.1%) mtDNA reached healthy adulthood, were fertile and most animals stably maintained the initial ratio of parental mtDNA heteroplasmy and donor mtDNA was transmitted from females to offspring. However, in one monkey out of four analyzed, initially negligible maternal mtDNA heteroplasmy levels increased substantially up to 17% in selected internal tissues and organs. In addition, two monkeys showed paternal mtDNA contribution up to 33% in selected internal tissues and organs. LARGE SCALE DATA N/A. LIMITATIONS, REASONS FOR CAUTION Conclusions in this study were made on a relatively low number of MRT monkeys, and on only one F1 (first generation) female. In addition, monkey MRT involved two wildtype mtDNA haplotypes, but not disease-relevant variants. Clinical trials on children born after MRT will be required to fully determine safety and efficacy of MRT for humans. WIDER IMPLICATIONS OF THE FINDINGS Our data show that MRT is compatible with normal postnatal development including overall health and reproductive fitness in nonhuman primates without any detected adverse effects. ‘Mismatched’ donor mtDNA in MRT animals even from the genetically distant mtDNA haplotypes did not cause secondary mitochondrial dysfunction. However, carry-over maternal or paternal mtDNA contributions increased substantially in selected internal tissues / organs of some MRT animals implying the possibility of mtDNA mutation recurrence. STUDY FUNDING/COMPETING INTEREST(S) This work has been funded by the grants from the Burroughs Wellcome Fund, the National Institutes of Health (RO1AG062459 and P51 OD011092), National Research Foundation of Korea (2018R1D1A1B07043216) and Oregon Health & Science University institutional funds. The authors declare no competing interests.

Mitochondrial replacement techniques (MRTs, also referred to as mitochondrial replacement therapies) have given hope to many women who wish to have genetically related children but have mitochondrial DNA mutations in their eggs. MRTs have also spurred deep ethical disagreements and led to different regulatory approaches worldwide. In this review, we discuss the current regulation of MRTs across several countries. After discussing the basics of the science, we describe the current law and policy directions in seven countries: the United Kingdom, the United States, Canada, Australia, Germany, Israel, and Singapore. We also discuss the emerging phenomenon of medical tourism (also called medical travel) for MRTs to places like Greece, Spain, Mexico, and Ukraine. We then pull out some key findings regarding similarities and differences in regulatory approaches around the world.

In 2015, the UK became the first country to approve the use of mitochondrial donation. This novel in vitro fertilisation treatment was developed to prevent transmission of mitochondrial DNA (mtDNA) disease and ultimately give more reproductive choice to women at risk of having severely affected offspring. The policy change was a major advance that surmounted many scientific, legislative and clinical challenges. Further challenges have since been addressed and there is now an NHS clinical service available to families with pathogenic mtDNA mutations that provides reproductive advice and options, and a research study to look at the outcome at 18 months of children born after mitochondrial donation.

In this review, conducted according to world literature, we sought to determine the role of mitochondrial DNA (mtDNA) in the formation of mitochondrial diseases. To determine the availability of treatment methods for hereditary diseases, in particular those associated with mitochondrial diseases, and to assess the role of mitochondrial replacement therapy (MRT) in assisted reproductive technologies. The scientific articles corresponding to the chosen goal are published on MEDLINE, EMBASE, in the Cochrane Library, PubMed, and other information sources. The search strategy combined the following search terms “mitochondrial diseases,” “mitochondrial replacement therapy,” “three-parent baby,” “ART,” “genetic engineering”.

Mitokondriler, neredeyse tüm insan hücrelerinde bulunan hücre içi organellerdir ve nükleusta bulunan çekirdek DNA molekülü haricinde özgül bir genetik materyale sahip yegâne organeldir. Mitokondriyal gen defektine bağlı olarak gelişen mitokondrinin işlevinin bozulması, semptom ve ağırlıkları değişen çeşitli mitokondriyal hastalığa ve sendromlara neden olur. Mitokondriyal hastalıklarda bugün için kesin küratif bir tedavi yoktur. Sağaltımı olmayan bu mitokondri hastalıklarında dönüm noktası; 2008 yılında Newcastle Üniversitesi’nden bilim insanlarının, mitokondriyal hastalıkları artık geçmişte bırakan bir kırılmanın müjdesini vermesi olmuştur: Bu kırılma “Mitokondri değiştirme tedavisi”dir. Bu yöntemle dünyaya gelen bebekler -kamuoyunda daha çok bilinen ismiyle üç ebeveynli bebek- üremeye yardımcı teknolojiler ve bilhassa manipüle edilmiş mitokondri kullanılarak, iki kadının ve bir erkeğin genetik materyalleri ile doğan bebeklerdir. Bu çalışmamızda mitokondri değiştirme tedavilerini tıbbi, etik ve hukuki yönleri ile ele alacağız.

It has recently been argued that reproductive genetic manipulation technologies like mitochondrial replacement and germline CRISPR modifications cannot be said to save anyone's life because, counterfactually, no one would suffer more or die sooner absent the intervention. The present article argues that, on the contrary, reproductive genetic manipulations may be life-saving (and, from this, have therapeutic value) under an appropriate population health perspective. As such, popular reports of reproductive genetic manipulations potentially saving lives or preventing disease are not necessarily mistaken, though such terminology still requires further empirical validation.

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.

Monogenic disorders occur at a high frequency in human populations and are commonly inherited through the germline. Unfortunately, once the mutation has been transmitted to a child, only limited treatment options are available in most cases. However, means of correcting disease-causing nuclear and mitochondrial DNA mutations in gametes or preimplantation embryos have now been developed and are commonly referred to as germline gene therapy (GGT). We will discuss these novel strategies and provide a path forward for safe, high-efficiency GGT that may provide a promising new paradigm for preventing the passage of deleterious genes from parent to child.

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.

Purpose of review Leber hereditary optic neuropathy (LHON) is the most common primary mitochondrial DNA (mtDNA) disorder in the population and it carries a poor visual prognosis. In this article, we review the development of treatment strategies for LHON, the evidence base and the areas of unmet clinical need. Recent findings There is accumulating evidence that increasing mitochondrial biogenesis could be an effective strategy for protecting retinal ganglion cells in LHON. A number of clinical trials are currently investigating the efficacy of viral-based gene therapy for patients harbouring the m.11778G>A mtDNA mutation. For female LHON carriers of childbearing age, mitochondrial replacement therapy is being offered to prevent the maternal transmission of pathogenic mtDNA mutations. Summary Although disease-modifying treatment options remain limited, a better understanding of the underlying disease mechanisms in LHON is paving the way for complementary neuroprotective and gene therapeutic strategies for this mitochondrial optic nerve disorder.

The purpose of the paper is to explore novel means to overcome the controversial ban in the USA against mitochondrial replacement therapy, a form of IVF, with the added step of replacing a woman’s diseased mutated mitochondria with a donor’s healthy mitochondria to prevent debilitating and often fatal mitochondrial diseases. Long proven effective in non-human species, MRT recently performed in Mexico resulted in the birth of a healthy baby boy. We explore the ethics of the ban, the concerns over hereditability of mitochondrial disease and its mathematical basis, the overlooked role of Mitochondrial Eve, the financial burden of mitochondrial diseases for taxpayers, and a woman’s reproductive rights. We examine applicable court cases, particularly protection of autonomy within the reproductive rights assured by Roe v Wade. We examine the consequences of misinterpreting MRT as genetic engineering in the congressional funding prohibitions causing the MRT ban by the FDA. Allowing MRT to take place in the USA would ensure a high standard of reproductive medicine and safety for afflicted women wishing to have genetically related children, concurrently alleviating the significant financial burden of mitochondrial diseases on its taxpayers. Since MRT does not modify any genome, it falls outside the “heritable genetic modification” terminology of concern to Congress and the FDA. Correcting this terminology, the IOM’s conclusion that MRT is ethical, the continuing normalcy of the first MRT recipient, and increasing public awareness of the promising benefits might be all that is required to modify the FDA’s position on MRT.

Questions over mitochondrial replacement suggest a role for mitochondrial DNA editing

Therapies for mitochondrial diseases has been largely limited to supportive and symptomatic therapies; however, in the last decade, advances in understanding the causes and pathomechanisms of these diverse disorders have enabled development of novel treatment strategies. Here, we highlight current use of dietary supplements and exercise therapy as well as emerging treatments in preclinical and clinical trial stages of development. Broad-spectrum therapies that may be applied multiple diseases include: activation of mitochondrial biogenesis, regulation of mitophagy and mitochondrial dynamics, bypass of mitochondrial biochemical defects, mitochondrial replacement therapy, and hypoxia. Tailored disease-specific therapies in development include: scavenging of toxic compounds, deoxynucleoside therapy, cell replacement therapies, viral-mediated gene-delivery, shifting heteroplasmy of mitochondrial DNA pathogenic variants, and stabilization of mitochondrial transfer RNAs.

Transferring nuclear material between mammalian oocytes or embryos from unrelated individuals offers an opportunity to exchange not only nuclear genetic materials but also their cytoplasm. The cytoplasm of a mammalian oocyte contains large amounts of mitochondria/mitochondrial (mt) DNA, which is maternally inherited. Given this unique feature of mitochondrial inheritance, it is feasible to replace mitochondria/mtDNA with donor cytoplasm if a reliable technology allowed for efficient transfer of only the nuclear material in eggs or in early embryos. Such a technology is deemed mitochondrial replacement therapy (MRT). MRT encompasses the potential utilization for germline gene therapy and for a theory for future assisted conception, which would overcome recurrent in vitro fertolization failure due to impaired cytoplasmic function (i.e., reproductive aging). In this chapter, the mitochondrial biogenesis in gametogenesis, during fertilization, early embryonic development, and mitochondrial disease; the research milestones and limitation of MRT; and MRT-derived potential application in future assisted conception were summarized.

The distinction between germline and somatic gene editing is fundamental to the ethics of human gene editing. Multiple conferences of scientists, ethicists, and policymakers, and multiple professional bodies, have called for moratoria on germline gene editing, and editing of human germline cells is considered to be an ethical "red line" that either never should be crossed, or should only be crossed with great caution and care. However, as research on germline gene editing has progressed, it has become clear that not all germline interventions are alike, and that these differences make a significant moral difference, when it comes to ethical questions about research, regulation, clinical application, and medical justification. In this paper, I argue that, rather than lumping all germline interventions together, we should distinguish between revising, correcting, and transferring genes, and I assess the consequences of this move for the ethics of gene editing.

Objectives Due to the maternally‐inherited nature of mitochondrial DNA (mtDNA), there is a lack of information regarding fetal mtDNA in the plasma of pregnant women. We aim to explore the presence and topologic forms of circulating fetal and maternal mtDNA molecules in surrogate pregnancies. Methods Genotypic differences between fetal and surrogate maternal mtDNA were used to identify the fetal and maternal mtDNA molecules in plasma. Plasma samples were obtained from the surrogate pregnant mothers. Using cleavage‐end signatures of BfaI restriction enzyme, linear and circular mtDNA molecules in maternal plasma could be differentiated. Results Fetal‐derived mtDNA molecules were mainly linear (median: 88%; range: 80%–96%), whereas approximately half of the maternal‐derived mtDNA molecules were circular (median: 51%; range: 42%–60%). The fetal DNA fraction of linear mtDNA was lower (median absolute difference: 9.8%; range: 1.1%–27%) than that of nuclear DNA (median: 20%; range: 9.7%–35%). The fetal‐derived linear mtDNA molecules were shorter than the maternal‐derived ones. Conclusion Fetal mtDNA is present in maternal plasma, and consists mainly of linear molecules. Surrogate pregnancies represent a valuable clinical scenario for exploring the biology and potential clinical applications of circulating mtDNA, for example, for pregnancies conceived following mitochondrial replacement therapy.

Despite recent striking advances in assisted reproductive technology (ART), poor ovarian response (POR) diagnosis and treatment is still considered challenging. Poor responders constitute a heterogeneous cohort with the common denominator of under-responding to controlled ovarian stimulation. Inevitably, respective success rates are significantly compromised. As POR pathophysiology entails the elusive factor of compromised ovarian function, both diagnosis and management fuel an ongoing heated debate depicted in the literature. From the criteria employed for diagnosis to the plethora of strategies and adjuvant therapies proposed, the conundrum of POR still puzzles the practitioner. What is more, novel treatment approaches from stem cell therapy and platelet-rich plasma intra-ovarian infusion to mitochondrial replacement therapy have emerged, albeit not claiming clinical routine status yet. The complex and time sensitive nature of this subgroup of infertile patients indicates the demand for a consensus on a horizontally accepted definition, diagnosis and subsequent effective treating strategy. This critical review analyzes the standing criteria employed in order to diagnose and aptly categorize POR patients, while it proceeds to critically evaluate current and novel strategies regarding their management. Discrepancies in diagnosis and respective implications are discussed, while the existing diversity in management options highlights the need for individualized management.

Conventional heterologous mitochondrial replacement therapy is clinically complicated by “triparental” ethical concerns and limited source of healthy donor oocytes or zygotes. Autologous mitochondrial transfer is a promising alternative in rescuing poor oocyte quality and impaired embryo developmental potential associated with mitochondrial disorders, including aging. However, the efficacy and safety of mitochondrial transfer from somatic cells remains largely controversial, and unsatisfying outcomes may be due to distinct mitochondrial state in somatic cells from that in oocytes. Here, we propose a potential strategy for improving in vitro fertilization (IVF) outcomes of aging female patients via mitochondrial transfer from induced pluripotent stem (iPS) cells. Using naturally aging mice and well-established cell lines as models, we found iPS cells and oocytes share similar mitochondrial morphology and functions, whereas the mitochondrial state in differentiated somatic cells is substantially different. By microinjection of isolated mitochondria into fertilized oocytes following IVF, our results indicate that mitochondrial transfer from iPS, but not MEF cells, can rescue the impaired developmental potential of embryos from aging female mice and obtain an enhanced implantation rate following embryo transfer. The beneficial effect may be explained by the fact that mitochondrial transfer from iPS cells not only compensates for aging-associated loss of mtDNA, but also rescues mitochondrial metabolism of subsequent preimplantation embryos. Using mitochondria from iPS cells as the donor, our study not only proposes a promising strategy for improving IVF outcomes of aging females, but also highlights the importance of synchronous mitochondrial state in supporting embryo developmental potential.Summary Sentence: Induced pluripotent stem cells are more preferred donors for mitochondrial transfer than differentiated somatic cells, for rescuing the impaired developmental potential of IVF embryos from aging females.Graphical Abstract

Legislation passed by the House of Lords in 2015 enabled mitochondrial replacement in the United Kingdom for the prevention of severe mitochondrial diseases. Regulation was delegated to the Human Fertilisation and Embryology Authority (HFEA) which granted its first licence to Newcastle upon Tyne Hospitals NHS Foundation Trust in 2017. Mitochondrial transfer, or “babies with three parents” as it was known in the lay press, is now a national commissioned NHS service in England and Wales. In 2016, it was reported that a woman gave birth to a healthy boy in Mexico following oocyte spindle transfer to prevent the inheritance of a mitochondrial DNA (mtDNA) disorder.1 Of particular concern, however, is that the technique has become available for the “treatment” of infertility at many fertility centres world-wide.2

Oocyte quality is one of the most important factors involving in female reproduction. The number of compromised oocytes will increase with maternal age, while mitochondrial dysfunction has implicated in age-related poor oocyte. Together with the successful application of ooplasmic transfer (OT) and the critical role of mitochondria in the oocyte, functional mitochondria transfer may be a feasible strategy to improve oocyte quality. However, limitation on ethics and laws are strictly and optimal condition or methods to exert transferring need to be further explored. Therefore, the role of oocyte mitochondria and the effective molecular involving in oocyte quality will be hot topics in next few years. In this review, we summarize the potential mechanism of mitochondria in oocyte and embryo development and discuss the next step for mitochondrial transfer therapy.

Background The first live birth following the use of a new reproductive technique, maternal spindle transfer (MST), which is a mitochondrial replacement technique (MRT), was accomplished by dividing the execution of the MST procedure between two countries, the USA and Mexico. This was done in order to avoid US legal restrictions on this technique. Sources of data Academic articles, news articles, documents obtained through freedom of information requests, laws, regulations and national reports. Areas of agreement MRTs are new reproductive techniques that present novel ethical and legal challenges, since genetic material from three people is employed to create a child. Areas of controversy Could the first MST procedure that culminated in a live birth negatively impact reproductive medicine in Mexico? Growing points The USA and Mexico need specific and clear legislation on MRTs, in order for such techniques not to be governed by prior existing legislation on assisted reproduction that is inadequate for dealing with the new challenges that these techniques present. Areas timely for developing research There is a pressing need for work to be done on the international governance of new reproductive techniques.

A clinical trial on mitochondrial replacement therapy (MRT) is currently being conducted and if this technique proves effective, National Health Service (NHS) England will fund MRT through the highly specialised services (HSS) funding stream. This paper considers whether MRT should be publicly funded by the NHS. Given the current financial pressure the NHS is experiencing, a comprehensive discussion is essential. There is yet to be a thorough discussion on MRT funding, perhaps because this is a small-scale issue and presumed to be covered by the HSS budget. However, the source of funding has not been confirmed due to the trial’s incompletion. Upon its completion, reasoned decisions need to be made over the allocation of scarce NHS resources. It is therefore important to consider the following arguments in advance. Three arguments given against NHS funding of MRT will be evaluated. The first argument against NHS funding examines the HSS overspending its budget in an underfunded NHS, suggesting funding must be carefully reprioritised. Second, the ethical issue of allowing public access to a technique with insufficient evidence behind it will be explored. The final point considers the option of privately funding MRT and how this would affect the treatment’s development. After illustrating the weaknesses of such arguments, it will be concluded that MRT should be funded by the NHS.

In this article, I draw on research carried out in Europe, primarily in Germany, on patients' and scientists' perspectives on mitochondrial replacement techniques (MRTs) in order to explore some of the complexities related to collective representation in health governance, which includes the translation of emerging technologies into clinical use. Focusing on observations, document analyses, and interviews with eight mitochondrial disease patient organization leaders, this contribution extends our understanding of the logic and meanings behind the ways in which patient participation and collective representation in health governance initiatives take shape. My findings highlight the ways in which a commitment to a global mitochondrial disease patient community and a sense of patient solidarity influence expressions of support with regard to legalizing mitochondrial replacement techniques. My analyses illustrate how normative practices and expectations of participatory governance potentially foreclose opportunities for sustained collective patient engagement with the complex ethical, social, and political dimensions of emerging technologies and may silence diverse and potentially dissenting embodied and lived responses to the prospects of particular technological developments.

We seek to develop a plausible conception of genetic parenthood, taking a recent discussion by Heidi Mertes as our point of departure. Mertes considers two conceptions of genetic parenthood—one invoking genetic resemblance and the other genetic inheritance—and presents counter‐examples to both conceptions. We revise Mertes’ second conception so as to avoid these and related counter‐examples.

For the vast majority of patients with mitochondrial diseases, only supportive and symptomatic therapies are available. However, in the last decade, due to extraordinary advances in defining the causes and pathomechanisms of these diverse disorders, new therapies are being developed in the laboratory and are entering human clinical trials. In this review, we highlight the current use of dietary supplement and exercise therapies as well as emerging therapies that may be broadly applicable across multiple mitochondrial diseases or tailored for specific disorders. Examples of non-tailored therapeutic targets include: activation of mitochondrial biogenesis, regulation of mitophagy and mitochondrial dynamics, bypass of biochemical defects, mitochondrial replacement therapy, and hypoxia. In contrast, tailored therapies are: scavenging of toxic compounds, deoxynucleoside and deoxynucleotide treatments, cell replacement therapies, gene therapy, shifting mitochondrial DNA mutation heteroplasmy, and stabilization of mutant mitochondrial transfer RNAs.

Background Mitochondrial replacement, a form of nuclear transfer, has been proposed as a germline therapy to prevent the transmission of mitochondrial diseases. Mitochondrial replacement therapy has been licensed for clinical application in the UK, and already carried out in other countries, but little is known about negative or unintended effects on the health of offspring born using this technique. Objective and rationale Studies in invertebrate models have used techniques that achieve mitochondrial replacement to create offspring with novel combinations of mitochondrial and nuclear genotype. These have demonstrated that the creation of novel mitochondrial-nuclear interactions can lead to alterations in offspring characteristics, such as development rates, fertility and longevity. However, it is currently unclear whether such interactions could similarly affect the outcomes of vertebrate biomedical studies, which have sought to assess the efficacy of the replacement therapy. Search methods This systematic review addresses whether the effects of mitochondrial replacement on offspring characteristics differ in magnitude between biological (conducted on invertebrate models, with an ecological or evolutionary focus) and biomedical studies (conducted on vertebrate models, with a clinical focus). Studies were selected based on a key-word search in 'Web of Science', complemented by backward searches of reviews on the topic of mitochondrial-nuclear (mito-nuclear) interactions. In total, 43 of the resulting 116 publications identified in the search contained reliable data to estimate effect sizes of mitochondrial replacement. We found no evidence of publication bias when examining effect-size estimates across sample sizes. Outcomes Mitochondrial replacement consistently altered the phenotype, with significant effects at several levels of organismal performance and health, including gene expression, anatomy, metabolism and life-history. Biomedical and biological studies, while differing in the methods used to achieve mitochondrial replacement, showed only marginally significant differences in effect-size estimates (-0.233 [CI: -0.495 to -0.011]), with larger effect-size estimates in biomedical studies (0.697 [CI: 0.450-0.956]) than biological studies (0.462 [CI: 0.287-0.688]). Humans showed stronger effects than other species. Effects of mitochondrial replacement were also stronger in species with a higher basal metabolic rate. Based on our results, we conducted the first formal risk analysis of mitochondrial replacement, and conservatively estimate negative effects in at least one in every 130 resulting offspring born to the therapy. Wider implications Our findings suggest that mitochondrial replacement may routinely affect offspring characteristics across a wide array of animal species, and that such effects are likely to extend to humans. Studies in invertebrate models have confirmed mito-nuclear interactions as the underpinning cause of organismal effects following mitochondrial replacement. This therefore suggests that mito-nuclear interactions are also likely to be contributing to effects seen in biomedical studies, on vertebrate models, whose effect sizes exceeded those of biological studies. Our results advocate the use of safeguards that could offset any negative effects (defining any unintended effect as being negative) mediated by mito-nuclear interactions following mitochondrial replacement in humans, such as mitochondrial genetic matching between donor and recipient. Our results also suggest that further research into the molecular nature of mito-nuclear interactions would be beneficial in refining the clinical application of mitochondrial replacement, and in establishing what degree of variation between donor and patient mitochondrial DNA haplotypes is acceptable to ensure 'haplotype matching'.

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.

In recent years mitochondrial DNA (mtDNA) has transitioned to greater prominence across diverse areas of biology and medicine. The recognition of mitochondria as a major biochemical hub, contributions of mitochondrial dysfunction to various diseases, and several high-profile attempts to prevent hereditary mtDNA disease through mitochondrial replacement therapy have roused interest in the organellar genome. Subsequently, attempts to manipulate mtDNA have been galvanized, although with few robust advances and much controversy. Re-engineered protein-only nucleases such as mtZFN and mitoTALEN function effectively in mammalian mitochondria, although efficient delivery of nucleic acids into the organelle remains elusive. Such an achievement, in concert with a mitochondria-adapted CRISPR/Cas9 platform, could prompt a revolution in mitochondrial genome engineering and biological understanding. However, the existence of an endogenous mechanism for nucleic acid import into mammalian mitochondria, a prerequisite for mitochondrial CRISPR/Cas9 gene editing, remains controversial., Trends Engineering of mammalian mtDNA has been hampered by an inability to import nucleic acids into mitochondria. A limited toolkit exists for manipulation of mammalian mtDNA, relying on protein-only nucleolysis and heteroplasmy-shifting approaches. Although present in lower metazoans, the weight of evidence against an efficient endogenous RNA import mechanism in mammalian mitochondria is considerable. Controversially, the application of CRISPR/Cas9 for manipulation of mammalian mtDNA in human cells has been reported.

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.

Novel technological developments mean that gene editing - making deliberately targeted alterations in specific genes - is now a clinical reality. The inherited metabolic disorders, a group of clinically significant, monogenic disorders, provide a useful paradigm to explore some of the many ethical issues that arise from this technological capability. Fundamental questions about the significance of the genome, and of manipulating it by selection or editing, are reviewed, and a particular focus on the legislative process that has permitted the development of mitochondrial donation techniques is considered. Ultimately, decisions about what we should do with gene editing must be determined by reference to other non-genomic texts that determine what it is to be human - rather than simply to undertake gene editing because it can be done.

With the recent report of a live birth after use of mitochondrial replacement therapy, sometimes called 'three-parent IVF', the clinical application of the technique is fast becoming a reality. While the United Kingdom allows the procedure under regulatory scrutiny, it remains effectively outlawed in many other countries. We argue that such prohibitions may violate individuals' procreative rights, grounded in individuals' interest in genetic affinity. The interest in genetic affinity was recently endorsed by Singapore's highest court, reflecting an emphasis on the importance of biological ties found across the globe. We apply that reasoning to make the case for a right to 'three-parent IVF'.

Recent developments in the field of mitochondrial replacement technique (MRT) research and clinical practice have raised ethical concerns worldwide. We argue that the future use of MRTs requires a concerted effort among the global research and clinical community to implement and enforce responsible innovation and governance.

Mitochondria, the ubiquitous power packs in nearly every eukaryotic cell, contain their own DNA, known as mtDNA, which is inherited exclusively from the mother. The number of mitochondrial genomes varies depending on the cell's energy needs. The mature oocyte contains the highest number of mitochondria of any cell type, although there is little if any mtDNA replication after fertilization until the embryo implants. This has potential repercussions for mitochondrial replacement therapy (MRT; see description of currently employed methods below) used to prevent the transmission of mtDNA‐based disorders. If only a few mitochondria with defective mtDNA are left in the embryo and undergo extensive replication, it might therefore thwart the purpose of MRT. In order to improve the safety and efficacy of this experimental therapy, we need a better understanding of how and which mtDNA is tagged for replication versus transcription after fertilization of the oocyte.

The ovarian reserve comprises an enormous surplus of follicles. Despite this, some women produce insufficient numbers of oocytes by conventional fertility treatments. However, recent technical accomplishments may transform assisted reproductive technology (ART) in such a way that oocytes are not necessarily the limiting factor. In this review, we present possible new strategies for enhancing the quantity of mature oocytes, and current views on autologous oocytes as potential sources of mitochondria to lift performance of compromised oocytes.New discoveries of the signaling pathways activating dormant follicles and breakthroughs in techniques for autologous transfer of mitochondria have opened new doors to unexploited sources of oocytes and attractive ways of revitalizing oocytes. Extended numbers of mature oocytes may be obtained by in-vitro activation of dormant follicles in cortical biopsies or in-vitro maturation of immature oocytes during the natural or stimulated cycle, and used directly for fertility treatment or as a source of autologous mitochondria.New approaches utilizing the abundant resources of immature oocytes combined with techniques for revitalizing deficient oocytes may transform ART, and potentially enhance both quantity and quality of fertilizable oocytes; hereby augmenting the pregnancy potential of women with poor reproductive performance.

The mitochondria contained in eukaryotic cells have their own DNA, and heritable mutations in mitochondrial DNA (mtDNA) can cause a variety of disorders in humans. A new therapy, mitochondrial replacement therapy (MRT), is currently being developed to address these mitochondrial disorders by eliminating the mutated mtDNA from the germline. The two main MRT techniques are pronuclear transfer, conducted in the zygote after fertilization, and spindle-chromosomal complex transfer, conducted in the oocyte before fertilization. In pronuclear transfer, the pronuclei from a zygote affected by a mtDNA mutation are transferred to an enucleated normal zygote. In spindle-chromosomal complex transfer, the genetic material from an oocyte affected by a mtDNA mutation is inserted into the cytoplasm of a donor oocyte that contains healthy mitochondria. A third method, polar body genome transfer, attempts to increase the efficiency of the above techniques by using polar bodies to supply the genetic material. While MRT is legally and ethically controversial, it has recently been implemented successfully in a clinical setting.