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Background Pathogenic mitochondrial (mt)DNA mutations, which often cause life‐threatening disorders, are maternally inherited via the cytoplasm of oocytes. Mitochondrial replacement therapy (MRT) is expected to prevent second‐generation transmission of mtDNA mutations. However, MRT may affect the function of respiratory chain complexes comprised of both nuclear and mitochondrial proteins. Methods Based on the literature and current regulatory guidelines (especially in Japan), we analyzed and reviewed the recent developments in human models of MRT. Main findings MRT does not compromise pre‐implantation development or stem cell isolation. Mitochondrial function in stem cells after MRT is also normal. Although mtDNA carryover is usually less than 0.5%, even low levels of heteroplasmy can affect the stability of the mtDNA genotype, and directional or stochastic mtDNA drift occurs in a subset of stem cell lines (mtDNA genetic drift). MRT could prevent serious genetic disorders from being passed on to the offspring. However, it should be noted that this technique currently poses significant risks for use in embryos designed for implantation. Conclusion The maternal genome is fundamentally compatible with different mitochondrial genotypes, and vertical inheritance is not required for normal mitochondrial function. Unresolved questions regarding mtDNA genetic drift can be addressed by basic research using MRT., This review discusses current approaches and legality regarding mitochondrial replacement for preventing the inheritance of mitochondrial diseases such as encephalomyopathy, cardiomyopathy, hearing loss, diabetes, and renal impairment, caused by pathogenic mutations in mtDNA. Although relevant advances have been achieved in the field of treatments for preventing mutant mtDNA transmission, some concerns and challenges remain such as mtDNA carryover, mtDNA genetic drift, and donor‐recipient compatibility.

Gene-targeted animal models that are generated by injecting Cas9 and sgRNAs into zygotes are often accompanied by undesired double-strand break (DSB)-induced byproducts and random biallelic targeting due to uncontrollable Cas9 targeting activity. Here, we establish a parental allele-specific gene-targeting (Past-CRISPR) method, based on the detailed observation that pronuclear transfer-mediated cytoplasmic dilution can effectively terminate Cas9 activity. We apply this method in embryos to efficiently target the given parental alleles of a gene of interest and observed little genomic mosaicism because of the spatiotemporal control of Cas9 activity. This method allows us to rapidly explore the function of individual parent-of-origin effects and to construct animal models with a single genomic change. More importantly, Past-CRISPR could also be used for therapeutic applications or disease model construction., Injecting Cas9 and gRNA into an animal zygote often produces mosaicism and random biallelic targeting. Here, the authors use pronuclear transfer to reduce mosaicism and selectively target parental alleles.

Primary mitochondrial diseases represent some of the most common and severe inherited metabolic disorders, affecting ~1 in 4,300 live births. The clinical and molecular diversity typified by mitochondrial diseases has contributed to the lack of licensed disease‐modifying therapies available. Management for the majority of patients is primarily supportive. The failure of clinical trials in mitochondrial diseases partly relates to the inefficacy of the compounds studied. However, it is also likely to be a consequence of the significant challenges faced by clinicians and researchers when designing trials for these disorders, which have historically been hampered by a lack of natural history data, biomarkers and outcome measures to detect a treatment effect. Encouragingly, over the past decade there have been significant advances in therapy development for mitochondrial diseases, with many small molecules now transitioning from preclinical to early phase human interventional studies. In this review, we present the treatments and management strategies currently available to people with mitochondrial disease. We evaluate the challenges and potential solutions to trial design and highlight the emerging pharmacological and genetic strategies that are moving from the laboratory to clinical trials for this group of disorders.

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.

The mitochondria are intracellular organelles, and just like the cell nucleus they have their own genome. They are extremely important for normal body functioning and are responsible for ATP production - the main energy source for the cell. Mitochondrial diseases are associated with mutations in mitochondrial DNA and are inherited exclusively from the mother. They can affect organs that depend on energy metabolism, such as skeletal muscles, the cardiac system, the central nervous system, the endocrine system, the retina and liver, causing various incurable diseases. Mitochondrial replacement techniques provide women with mitochondrial defects a chance to have normal biological children. The goal of such treatment is to reconstruct functional oocytes and zygotes, in order to avoid the inheritance of mutated genes; for this the nuclear genome is withdrawn from an oocyte or zygotes, which carries mitochondrial mutations, and is implanted in a normal anucleated cell donor. Currently, the options of a couple to prevent the transmission of mitochondrial diseases are limited, and mitochondrial donation techniques provide women with mitochondrial defects a chance to have normal children. The nuclear genome can be transferred from oocytes or zygotes using techniques such as pronuclear transfer, spindle transfer, polar body transfer and germinal vesicle transfer. This study presents a review of developed mitochondrial substitution techniques, and its ability to prevent hereditary diseases.

The field of reproductive medicine has been criticized for introducing ARTs without systematic research on possible safety risks and for failing to meet the standards of evidence-based innovation held elsewhere in medicine. In this paper, firstly, we ask whether ‘responsible innovation’ has been a concern for the field, and if so, how it has understood the practical implications of this idea for the development and introduction of potentially risky new ARTs. Secondly, we consider whether the field has indeed fallen short of its responsibilities in this respect, and if so, how things can be improved. To answer these questions, we present three case studies involving the introduction of a new reproductive technology: ICSI, preimplantation genetic testing and mitochondrial replacement therapy. As a framework for analyzing these cases, we used Per Sandin’s account of the four dimensions of dealing with risks (threat, uncertainty, action, command) that are central to debates about the possible role of the so-called precautionary principle. We conclude that, although offspring safety concerns have been on the agenda of the debate about bringing the relevant technologies to the clinic, systematic safety and effectiveness studies were not always conducted. As professionals in assisted reproduction have a responsibility to take account of the welfare of the children they are creating, we suggest a policy of proceeding with systematic caution. Legal measures may be needed to ensure that professional guidance is followed in practice. Finally, an open question concerns the threshold for acceptable risk in the context of introducing new ARTs. Multiple stakeholders, including professional societies and patient organizations, should have a role in the urgent debate about this.

This study was designed to assess the mitochondrial disease community’s knowledge, attitude and perception of mitochondrial replacement therapy (MRT) and determine how the media can impact such perception. MRT in conjunction with in vitro fertilization (IVF) has the ability to prevent inheritance of mitochondrial DNA (mtDNA) mutations from mothers to their offspring by using a donor egg’s mtDNA. The Federal Drug Administration (FDA) is considering human trials for MRT, dubbed “three-parent IVF” by the media. Approval relies heavily on the mitochondrial disease community’s willingness to participate; however, the community’s perceptions of risks, benefits and limitations associated with MRT have not been adequately addressed. An anonymous survey was distributed online to individuals within the mitochondrial community; 165 individuals completed the survey and comprised the study population. The majority of individuals found MRT ethical, agreed with FDA approval for human clinical trials, and would be willing to use MRT if clinically appropriate and available. However, almost half were unaware that MRT is only useful if a mtDNA mutation has been previously identified. Many respondents knew this technique does not change physical or personality traits of offspring; however, those who believed it did also felt more strongly that this technique is “designing babies”. Interestingly, the majority did not believe that the children born using MRT have three parents, so the media’s use of “three-parent baby” may be unnecessarily sensationalized. Our results provide evidence that the mitochondrial disease community is forward-thinking about MRT; however, may not be adequately aware of MRT’s risks or limitations.

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.

Mitochondrial DNA (mtDNA) is predominately uniparentally transmitted. This results in organisms with a single type of mtDNA (homoplasmy), but two or more mtDNA haplotypes have been observed in low frequency in several species (heteroplasmy). In this review, we aim to highlight several aspects of heteroplasmy regarding its origin and its significance on mtDNA function and evolution, which has been progressively recognized in the last several years. Heteroplasmic organisms commonly occur through somatic mutations during an individual’s lifetime. They also occur due to leakage of paternal mtDNA, which rarely happens during fertilization. Alternatively, heteroplasmy can be potentially inherited maternally if an egg is already heteroplasmic. Recent advances in sequencing techniques have increased the ability to detect and quantify heteroplasmy and have revealed that mitochondrial DNA copies in the nucleus (NUMTs) can imitate true heteroplasmy. Heteroplasmy can have significant evolutionary consequences on the survival of mtDNA from the accumulation of deleterious mutations and for its coevolution with the nuclear genome. Particularly in humans, heteroplasmy plays an important role in the emergence of mitochondrial diseases and determines the success of the mitochondrial replacement therapy, a recent method that has been developed to cure mitochondrial diseases.

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.

Mitochondria are essential parts of living cells, as they play a key role in cellular metabolism, especially in energy production. Due to their unique structure, the energy released during the oxidation of the substrates can be used to form the ATP. Mitochondria also contain their own DNA (mtDNA), which is maternally inherited and encodes catalytic subunits of oxidative phosphorylation complexes. Mitochondrial disorders of nuclear or mitochondrial origin, are common causes of inherited diseases and affect mainly the tissues with high energy requirements, such as heart or brain. Treatment of mitochondrial diseases is usually symptomatic and does not lead to complete recovery of the patient. As a result, new causal therapies, such as a gene therapy, are currently investigated. However, using this approach it is necessary to consider the origin of the mutation. Gene therapy of mitochondrial diseases of mtDNA origin is very complicated, therefore the new treatment strategy, mitochondrial replacement therapy, has been proposed. The principle of this technique is to prevent the transmission of mutated mtDNA from mother to offspring by transferring the nuclear genome of mother with mitochondrial disorder into donor's denucleated oocyte with healthy mitochondria. In this way, the child has genetic...

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.

Mitochondrial replacement therapy (MRT) is a new form of reproductive invitro fertilization (IVF) which works on the principle of replacing a women's abnormal mitochondrial DNA (mt-DNA) with the donor's healthy one. MRT include different techniques like spindles transfer (ST), pronuclear transfer (PNT) or polar body transfer (PBT). Transmission of defective mitochondrial DNA to the next generation can also be prevented by using these approaches. The development of healthy baby free from genetic disorders and to terminate the lethal mitochondrial disorders are the chief motive of this technique. In aged individuals, through in vitro fertilization, MRT provides the substitution of defective cytoplasm with cured one to enhance the expectation of pregnancy rates. However, moral, social, and cultural objections have restricted its exploration. Therefore, this review summarizes the various methods involved in MRT, its global status, its exaggerated censure over the years which depicts a strong emphasis for social acceptance and clinical application in the world of medical science., Genetics, Molecular Biology, Stem Cell Research, Cancer research; Biological sciences; Mitochondrial Replacement therapies; IVF; mitochondrial disorders; genetic anomalies.

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.

Mitochondria are energy-producing intracellular organelles containing their own genetic material in the form of mitochondrial DNA (mtDNA), which codes for proteins and RNAs essential for mitochondrial function. Some mtDNA mutations can cause mitochondria-related diseases. Mitochondrial diseases are a heterogeneous group of inherited disorders with no cure, in which mutated mtDNA is passed from mothers to offspring via maternal egg cytoplasm. Mitochondrial replacement (MR) is a genome transfer technology in which mtDNA carrying disease-related mutations is replaced by presumably disease-free mtDNA. This therapy aims at preventing the transmission of known disease-causing mitochondria to the next generation. Here, a proof of concept for the specific removal or editing of mtDNA disease-related mutations by genome editing is introduced. Although the amount of mtDNA carryover introduced into human oocytes during nuclear transfer is low, the safety of mtDNA heteroplasmy remains a concern. This is particularly true regarding donor-recipient mtDNA mismatch (mtDNA–mtDNA), mtDNA-nuclear DNA (nDNA) mismatch caused by mixing recipient nDNA with donor mtDNA, and mtDNA replicative segregation. These conditions can lead to mtDNA genetic drift and reversion to the original genotype. In this review, we address the current state of knowledge regarding nuclear transplantation for preventing the inheritance of mitochondrial diseases.

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.

Ovarian insufficiency is described as a multifaceted issue typically encountered in the field of assisted reproduction. The three main identified diagnoses of ovarian insufficiency include premature ovarian failure (POF), poor ovarian response (POR), and advanced maternal age (AMA). Patient heterogeneity in the era of individualized medicine drives research forward leading to the emergence of novel approaches. This plethora of innovative treatments in the service of adequately managing ovarian insufficiency is called to undertake the challenge of addressing infertile patients exploring their reproductive options. This review provides an all-inclusive presentation and critical analysis on novel treatments that have not achieved routine clinical practice status yet, but have recently emerged as promising. In light of the lack of randomized controlled trials conveying safety and efficiency, clinicians are left puzzled in addressing the “how” and “for whom” these approaches may be beneficial. From ovarian injection employing platelet-rich plasma (PRP) or stem cells to artificial gametes and ovaries, ovarian transplantation, and mitochondrial replacement therapy, this descriptive review provides insight toward assisting the practitioner in decision making regarding these cutting-edge treatments. Biological mechanisms, invasiveness levels, efficiency, as well as possible complications, the current status along with bioethical concerns are discussed in the context of identifying future optimal treatment.

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

The developmental potential of early embryos is mainly dictated by the quality of the oocyte. Here, we explore the utility of the maternal spindle transfer (MST) technique as a reproductive approach to enhance oocyte developmental competence. Our proof-of-concept experiments show that replacement of the entire cytoplasm of oocytes from a sensitive mouse strain overcomes massive embryo developmental arrest characteristic of non-manipulated oocytes. Genetic analysis confirmed minimal carryover of mtDNA following MST. Resulting mice showed low heteroplasmy levels in multiple organs at adult age, normal histology and fertility. Mice were followed for five generations (F5), revealing that heteroplasmy was reduced in F2 mice and was undetectable in the subsequent generations. This pre-clinical model demonstrates the high efficiency and potential of the MST technique, not only to prevent the transmission of mtDNA mutations, but also as a new potential treatment for patients with certain forms of infertility refractory to current clinical strategies., eLife digest Infertility is a growing problem that affects millions of people worldwide. Medical procedures known as in vitro fertilization (IVF) help many individuals experiencing infertility to have children. Typically in IVF, a woman’s egg cells are collected, fertilized with sperm from a chosen male and grown for a few days in a laboratory, before returning them to the woman’s body to continue to develop. However, there are some women whose egg cells cannot develop into a healthy baby after they have been fertilized. Many of these patients use egg cells from donors, instead. This greatly improves the chances of the IVF treatment being successful, but the resultant children are not genetically related to the intended mothers. Previous studies suggested that a cell compartment known as the cytoplasm plays a crucial role in allowing fertilized egg cells to develop normally. A new technique known as maternal spindle transfer, often shortened to MST, makes it possible to replace the entire cytoplasm of a compromised egg cell. This is achieved by transplanting the genetic material of the compromised egg cell into a donor egg cell with healthier cytoplasm that has previously had its own genetic material removed. Using this technique, it is possible to generate human egg cells for IVF that have the genetic material from the intended mother without the defects in the cytoplasm that may be responsible for infertility. However, it is not clear whether this approach would be a safe and effective way to treat infertility in humans. Costa-Borges et al. applied MST to infertile female mice and found that the technique could permanently correct deficiencies in the cytoplasms of poor quality egg cells, allowing the mice to give birth to healthy offspring. Further experiments studied the offspring and their descendants over several generations and found that they also had higher quality egg cells and normal levels of fertility. These findings open up the possibility of developing new treatments for infertility caused by problems with egg cells, so experiments involving human egg cells are now being performed to evaluate the safety and effectiveness of the technique.

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.

First medical contact for couples trying for a child will usually emphasise the array of assistance available to ‘help them have their own child’, usually with options involving ART, after diagnosis. For many poorer prognosis couples, this means repetitive unsuccessful cycles of invasive and stressful treatment. What is sometimes lost at this stage is a reflection on the likelihood of success of different options, which may lead patients to focus on hoping for their own ‘genetic’ progeny, but failing to consider the alternative and potentially more successful other options, including donation and adoption, for achieving parenthood of a child. Factors not only such as female age but also advanced requirements such as preimplantation genetic testing or even mitochondrial replacement therapies all have reduced chances of success but further tend to reinforce the importance of a genetic link. The financial, physical and psychosocial burden associated with cumulative failure also lead to a higher probability of dropout and consequently an even higher probability of remaining in involuntary childlessness. We advocate formulation of a detailed roadmap for discussion of parenthood, with reference explanation to genetics and epigenetics, which gives due consideration to the psychological effects from the beginning to end of the treatment process, alongside a balanced consideration of the likelihood of treatment success and discussion of other options. Only when we provide patients with the service of a clear and transparent discussion of these matters, we will really realise the true potential of our field, which may then be better considered as assisted families.