Introduction
Since the birth of the first baby conceived through in vitro fertilization (IVF) in 1978, the use of assisted reproductive technologies (ART) has increased steadily worldwide.Reference Sullivan, Zegers-Hochschild and Mansour 1 ART has also increased in diversity over time to include not only IVF, but also intracytoplasmic sperm injection (ICSI) and preimplantation genetic screening. In the United States, the number of children born from ART has tripled between 1996 and 2010, with 1.6% of all births in 2013 being conceived through ART.Reference Sunderam, Kissin and Crawford 2
Over the last decade, several animal studies and an increasing number of studies in humans have reported that the epigenetic reprogramming of embryos could be disrupted by different steps involved in ART,Reference Ventura-Juncá, Irarrázaval and Rolle 3 meaning that ART-conceived children could be at higher risk of developing particular diseases later in life. This opens new avenues for considering the Developmental Origins of Health and Disease (DOHaD), pointing to the earliest possible developmental starting point. Moreover, some ART-induced epigenetic risks could be passed on to future generations.Reference Daxinger and Whitelaw 4 Epigenetic risks associated with ART raise a number of ethical and societal questions for health professionals, prospective parents and children, and society. For instance, it is yet unclear whether possible epigenetic harm to future children – and potentially future generations – could be a convincing and ethically coherent argument for restricting access to ART, and if so, to what extent.
This paper explores the notion that ART clinics should attempt to take epigenetic risks into account when informing and treating patients. It focuses on the implications of such attempts for clinical practice and on the ethical obligations that it may entail. We build on the well-established principlist approach developed in 1979 by Beauchamp and Childress in their seminal book Principles of Biomedical Ethics. This approach is based on the analysis of ethical tensions through the application of four cornerstone ethical principles: respect for autonomy, beneficence, non-maleficence and justice.Reference Beauchamp and Childress 5 The relevance and meaning of each of these principles is determined with regards to the specific context and issue at stake before balancing the principles against each other to determine which one should prevail in a given case.
First, we describe recent associations between ART and epigenetic risks. Second, we describe the ethical tension that arises from the apparent dual commitment of health professionals to promote the reproductive autonomy of parents (respect for autonomy) and to minimize risks for children (non-maleficence). We also consider the implications of the ‘non-identity problem’ in this context. We discuss the communication of epigenetic risks associated with ART to patients. We highlight the difficulty of deciding when emerging evidence is robust enough to warrant such communication and the challenge of communicating complex risk information in an accessible way. We argue that – when appropriate – the discussion of epigenetic risks with potential patients can promote informed consent, which is an important aspect of reproductive autonomy. Finally, we discuss the research and policy implications of the epigenetic risks associated with ART, arguing for more research to assess those risks and for guidelines for effective communication with prospective parents.
Epigenetic reprogramming and epigenetic risks associated with ART
Epigenetic reprogramming occurs soon after fertilization in the maternal and paternal genomes of the newly formed zygote. It involves the erasure of the epigenetic marks – such as DNA methylation and histone modifications – present in the gametes of the parents. Such a reset is necessary in order to reprogram cells as totipotent and pluripotent and allow cellular differentiation.Reference Cantone and Fisher 6 , Reference Morgan, Santos, Green, Dean and Reik 7 Epigenetic reprogramming is a crucial step in the embryo’s development, and is to a certain extent sensitive to environmental signals such as nutrition, hormones and drugs.Reference Hochberg, Feil and Constancia 8 For this reason, epigenetic reprogramming could be impaired by ART, leading to modifications that could have an impact on the resulting child’s future health. ART may also disrupt normal genomic imprinting, that is, the silencing of specific alleles by epigenetic marks, in animalsReference Young, Sinclair and Wilmut 9 , Reference Khosla, Dean, Brown, Reik and Feil 10 and humans,Reference DeBaun, Niemitz and Feinberg 11 , Reference Cox, Bürger and Lip 12 also resulting in potential impact on future health.
Ventura-Juncá et al.Reference Ventura-Juncá, Irarrázaval and Rolle 3 recently reviewed evidence from animal studies showing that ovulation induction, in vitro maturation of gametes, fertilization technique and embryo culture, manipulation and transfer, could be responsible for disrupted epigenetic reprogramming. They report, for instance, that hormones used in ovarian stimulation may affect levels of DNA methylation in the blastocyst in a dose-dependent manner and that oocytes obtained through ovarian stimulation display patterns of abnormal imprinting in some genes. Moreover, embryos conceived with oocytes derived from ovulation stimulation were shown to exhibit defective epigenetic programming in somatic tissue, and embryo culture itself has been shown to impair epigenetic reprogramming.Reference Ventura-Juncá, Irarrázaval and Rolle 3
Fertilization method seems to also impact epigenetic reprogramming. ICSI, which was initially developed to treat male-factor infertility, is now used as the preferred fertilization technique in humans.Reference Nygren and Andersen 13 However, ICSI has been associated with epigenetic alterations in animals as well as imprinting syndromes in humans, such as the Beckwith–Wiedemann syndrome (BWS)Reference DeBaun, Niemitz and Feinberg 11 , Reference Chang, Moley, Wangler, Feinberg and DeBaun 14 – Reference Maher, Brueton and Bowdin 16 and the Angelman syndrome (AS).Reference Cox, Bürger and Lip 12 , Reference Ørstavik, Eiklid and van der Hagen 17 More generally, ART could be involved in various development malformations (i.e. related to implantation, placentation, organ formation and fetal growth) through defective epigenetic reprogramming of developmental genes.Reference Horsthemke and Ludwig 18 In addition, recent studies have suggested that ART could be responsible for cardiometabolic abnormalities such as higher blood pressure, reduced insulin sensitivity and altered glucose metabolism in ART-conceived offspring. Similarly, these variations could result from impaired epigenetic programming.Reference Seggers, Haadsma and La Bastide-Van Gemert 19 – Reference Ceelen, van Weissenbruch, Vermeiden, van Leeuwen and Delemarre-van de Waal 22 This is in accordance with the DOHaD hypothesis, which states that exposure to environmental stressors during fetal development and early childhood can affect one’s health in adulthood.Reference Vrooman and Bartolomei 23 However, empirical data supporting the hypothesis that ART causes epigenetic risks are still sparse. ART has been used for <40 years and only recent studies have started to identify and characterize its long-term consequences on health. Although uncertainty remains regarding the potential adverse epigenetic effects of ART on humans, it appears that almost every step involved in ART – before, during or after fertilization – may disturb the epigenome to some extent.
The gradual emergence of a body of evidence regarding the adverse epigenetic impact of ART raises challenging ethical issues regarding the obligations of health professionals, professional societies and policy-makers. If robust evidence is accumulated regarding the possible epigenetic harms involved in ART and their impact on future health, how should this influence the way in which we conduct and regulate ART, and the way we inform patients? As will be detailed in the following two sections, the main ethical tension that arises with recent scientific findings about the potential epigenetic risks of ART resides in a dilemma between respect of parental autonomy to use it, and the principle of non-maleficence, which calls for the protection of future children from epigenetic harm.
Possible tension between health professionals and prospective parents
An ethical tension could arise if prospective parents (i.e. potential IVF users) request to use ART, whereas professionals believe that the epigenetic risk involved poses a serious threat to the well-being of the child that would be conceived. In terms of ethical principles, this would translate into a tension between the principle of respect for autonomy (and more specifically reproductive autonomy) and that of non-maleficence or ‘do no harm.’
Reproductive autonomy
The principle of respect for autonomy is a core principle in liberal democratic societies.Reference Brock 24 This principle, which is closely tied to the right to self-determination, has underlined the development of the field of bioethics since the 1960s. The rise of bioethics in the United States as a social movement as well as an academic field of study was fueled by a series of scandals (such as the Tuskegee trialReference Beauchamp and Childress 5 ) that led the public to question the ethical acceptability of medical paternalism and to highlight the importance of individuals’ right to self-determination in the context of medical care and medical research. The principle of respect for autonomy is most notably expressed through the process of obtaining free and informed consent from patients and research participants. Today, respect for autonomy is a cornerstone ethical principle in healthcare and research, and patients are seen as primary decision-makers about their health and the interventions they wish to undergo.
In the context of reproduction, respect for autonomy means that individuals should have the opportunity to choose whether or not to procreate and by what means.Reference Robertson 25 Importantly, the available procreative options might differ depending on individuals and context. For infertile individuals, ART is the only way of having a genetically or biologically related child. For carriers of deleterious genetic mutations, ART allows for the selection of healthy embryos which may represent for prospective parents the only responsible way of conceiving. Hence, respecting individuals’ wishes to use ART, and facilitating their access to it, is often seen as expressing respect for their reproductive autonomy.Reference Quigley 26
The right to reproductive autonomy is generally understood as a ‘negative right.’ Negative rights are liberty rights or rights to non-interference, such as the right to freedom of expression. In this case, it is the right to keep third parties (such as the state or other individuals) from interfering with one’s reproductive choices.Reference Robertson 25 It means, for example, that nobody is allowed to sterilize individuals without their informed consent. However, in cases where ART is required to achieve the desired goal of a pregnancy, it has been suggested that reproductive autonomy may entail ‘positive rights’ as well.Reference Quigley 26 Positive rights are rights to assistance and social support, such as the right to education or to health. In this case, it would be the right of those in need of ART not only to access the services they need without interference, but even to have access to public funding for ART. It may also entail an ethical obligation to help prospective parents achieve a pregnancy using the required techniques.Reference Daar 27 The principle of reproductive autonomy thus means that we should accord great importance to the desire of individuals to access ART in order to become parents. This importance means that refusing to provide the needed assistance or creating barriers to access to ART would require particularly strong justifications.
Non-maleficence and the prevention of epigenetic harm
Respect for reproductive autonomy is not the only ethical consideration in the context of ART. A second key consideration is the principle of non-maleficence, which is the modern iteration of the ancient maxim of medical ethics primum non nocere (first, do no harm) that appears already in the Hippocratic Oath.Reference Beauchamp and Childress 5 As numerous medical interventions may cause harm to the patient, with the eventual goal of doing good (e.g. detrimental effects of chemotherapy with the objective of curing cancer), the duty to not cause harm has to be balanced against the duty to do good, that is the principle of beneficence. In the context of ART this translates, for example, into balancing the risks of ART for the mother, such as ovarian hyperstimulation syndrome,Reference Vloeberghs, Peeraer, Pexsters and D’Hooghe 28 with the potential social and psychological burdens of infertility. With regards to the epigenetic risks that ART may represent for the prospective child, the principle of non-maleficence requires that professionals do their best to protect that child from those risks, or at least minimize them.
What makes ART’s potential epigenetic risks sensitive is that protecting the prospective child from these inherent risks may conflict with the desire of prospective parents to use ART in order to conceive. This could create an ethical tension for professionals who would find themselves torn between the ethical obligation to respect reproductive autonomy (i.e. respect patients’ requests) and that of refraining from harm (i.e. refusing to provide ART in order to protect the child it might create).
Specific features of this ethical tension
The ethical tension described above occurs in fertility clinics when individuals request the use of ART, but professionals believe that if they acquiesce, the resulting child may be at risk of harm. This belief is usually based on an assessment of certain characteristics of the prospective parents, that make professionals question their future parental capability and hence the safety and well-being of a child they would raise. Professionals describe various circumstances that raise such concerns, such as mental health, substance abuse, negligence or abuse of existing children, marital strife, and even very difficult socio-economic conditions.Reference Hunfeld, Passchier, Bolt and Buijsen 29 – Reference Záchia, Knauth and Goldim 33 Numerous arguments can be made for and against allowing health professionals to be ‘gate keepers’ and to have the moral authority to decide whom to treat and whom to reject. What is certain, though, is that they themselves experience such circumstances as ethically challenging. From their perspective, the ethical tension between their obligation to respect reproductive autonomy and to protect prospective children from harm is real and acute.
Will similar tensions arise in the case of epigenetic risks? There is a key conceptual difference between these two scenarios. The scenario of questioning parental capability – and hence the safety and well-being of prospective children – is limited to certain individuals who display specific characteristics. The epigenetic risks discussed in this paper are inherent and specific to the process of ART itself. The ethical issues they raise thus apply to all prospective parents, regardless of their specific characteristics or life circumstances. Of course, this is not to say that other important factors such as parental ageReference Brion, Leary, Lawlor, Smith and Ness 34 or obesityReference Drake and Reynolds 35 cannot additionally increase epigenetic risks for the future child. In fact, those have been suggested to increase the probability that children will suffer from metabolic conditions related to epigenetic alterations. However, we argue that the tension between individuals’ desire to use ART and such inherent risks involved in ART is of a different nature. It is not a tension that can be assessed and managed on a case-by-case basis, but is rather one that applies to the entire enterprise of ART. An argument against the use of ART due to epigenetic risks is an argument against all ART, not against its use by specific individuals.
The implications of this distinction are important for health professionals. Although assessing parental capacity on a case-by-case basis requires an engagement with the specific circumstances of each case, the challenge raised by epigenetic risks associated with ART is uniform, as it is inherent to the use of certain procedures and technologies. This means that addressing this challenge should not be the responsibility of individual clinicians or even clinics, but rather a task tackled at a higher level, that is, by regulators and policy-makers. Professional societies such as the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society could also play a role in implementing better informed consent procedures and guidelines for transparent and proportional communication of epigenetic risks. Striking the ethically responsible balance between the use of ART to alleviate infertility and suffering, and the protection of future generations from increased risk caused by ART, is a complex matter that deserves systemic reflection. This matter is further complicated by the fact that the evidence regarding ART-associated risks is emerging gradually. This means that a concerted decision needs to be made regarding the appropriate point in time in which this evidence is robust enough to be communicated to patients. This issue is particularly challenging, because it would require communicating information about risk, not about certain outcomes to prospective parents. It is well documented that risk communication poses unique challenges and that the understanding and integration of risk information into decision-making is exceptionally difficult for patients.Reference Bogardus, Holmboe and Jekel 36
The non-identity problem (NIP)
Another conceptual challenge that touches on the possible ethical tension between respect for reproductive autonomy and non-maleficence is related to the fact that in the context of ART, the child whose well-being is in question does not exist. Rather, it is precisely the conception of that child that is at stake. Can we argue that we are acting ‘in the best interest’ of a specific child when what we do, in reality, is preventing her or his birth? Is it reasonable to argue that the risks inherent to the procedure necessary to conceive are so serious that by preventing birth we are benefitting the child? This challenge is known in the philosophical literature as the ‘non-identity problem.’Reference Parfit 37 This problem stems from situations where in order to avoid or mitigate risk or harm to future children we need to prevent their conception. In these cases, it is unclear whether avoiding conception ‘improves’ the situation of the child in question (i.e. the child we were about to conceive).
Consider the following example. A couple wishes to conceive, but if they proceed now, the resulting child (child A) will be at greater risk of being disabled than if they wait 2 months before conceiving (resulting in child B). Intuitively, most people would say that the couple should wait 2 months in order to minimize the risk of having a disabled child. However, from a logical standpoint, postponing conception would not improve child A’s outcome, because by doing so, child A would not be born at all. Rather, child B would be born, and would be a different individual than child A, with a completely distinct identity. As we cannot reasonably compare the flawed existence of child A with its ‘non-existence,’ it then seems counter-intuitive to argue that it would be in the best interest of the child to wait 2 months before conception. The NIP thus describes a conflict between our ethical intuitions and the outcome of this logical argument.
In the context of ART, a similar conundrum arises. It stems from the intuition that, when aware of the epigenetic risks of ART, health professionals and parents caring for the health and well-being of the future child should decide to avoid ART. Although epigenetic risks related to ART seem to call for precaution and the protection of future children from harm, the NIP strikes again. This is the case because the use of another conception method – or simply not using ART in the case of infertile patients – would prevent the existence of the child or change the identity of the resulting child. Therefore, as explained above, we could not say that the alternative improves the overall situation of the child that would have been conceived by ART.
The NIP could prompt us to believe that the principle of non-maleficence does not apply in the context of ART. From this perspective, the reproductive autonomy of prospective parents seeking to conceive by ART should prevail regardless of the risks associated with the procedure. However, an important nuance must be taken into account. For the NIP to apply, a distinction needs to be made between ‘identity-preserving’ and ‘identity-altering’ interventions. As the genetic identity of the prospective child is determined at the time of conception, it has been argued that any intervention that changes the circumstances of conception should be considered ‘identity altering,’ whereas any intervention that occurs after conception would be ‘identity preserving.’Reference Hope and McMillan 38, Footnote a
Therefore, with respect to the NIP, healthcare professionals and prospective parents should not be considered to violate the principle of non-maleficence when using pre-conception ART. Even though some steps before fertilization (i.e. superovulation and gamete maturation) and during fertilization (i.e. IVF or ICSI) seem to cause epigenetic risk, the NIP precludes an appeal to the principle of non-maleficence, thus paving the way for the promotion of reproductive autonomy. However, when it comes to post-conception or post-fertilization technologies (e.g. culture media or cryopreservation of embryos, post-fertilization mitochondrial replacement), it seems that healthcare professionals would carry an ethical duty to minimize harm and maximize benefit for the embryo in question. Put simply, according to the NIP, health professionals should minimize epigenetic risks of ART by making appropriate choices from the moment of conception, but are not morally obliged to do so before conception.
Implications of ART-associated epigenetic risks: the importance of responsible communication
The principle of respect for autonomy is broader than mere compliance of health professional with the requests of their patients. This perspective is incomplete, because it fails to fully acknowledge an important aspect of decision making that makes reproductive autonomy actionable. Autonomous decisions are not only those that are free of any pressure or coercion, they are also well-informed decisions. In the case of ART, parents’ reproductive autonomy requires that they be appropriately informed regarding the epigenetic risks associated with the ART procedures they are choosing. It is thus the health professionals’ duty to provide the relevant information so that parents can provide free and informed consent.
It may be difficult, though, to determine what information should be disclosed in order for the decision to actually be informed. Information regarding the epigenetic risks associated with ART is complex and involves uncertainty, which is – as noted above – especially difficult to communicate in clinical settings.Reference Han 40 Some of the uncertainty stems from the fact that most data supporting the hypothesis that ART poses an epigenetic risk comes from animal experiments, and that cohort studies have not yet been able to confirm this hypothesis in humans.Reference Amor and Halliday 41 – Reference Bowdin, Allen and Kirby 44
For example, although it has been suggested that large offspring syndrome in bovine, which shows several similarities with BWS and has been associated with ART in animals, could be used as a model to study BWS in humans,Reference Chen, Robbins, Wells and Rivera 45 not all evidence regarding the epigenetic defects associated with ART can be translated from animals to humans as most of it comes from experiments in rodents. Also, the evidence in humans that does support the hypothesis that ART could pose epigenetic risks is still relatively scant and methodological shortcomings such as small sample size and reporting bias limit the significance of these studies.Reference DeBaun, Niemitz and Feinberg 11 , Reference Chang, Moley, Wangler, Feinberg and DeBaun 14 Moreover, in all instances where ART is associated with a higher risk of diseases or disorders, including imprinting disorders, it is difficult to distinguish between the effect of infertility and that of the reproductive technique.Reference Ludwig, Katalinic and Gross 46 , Reference Buckett and Tan 47
Concealing information from patients in order to avoid misunderstanding is paternalistic and ethically unacceptable, especially when it is relevant and actionable. According to Beauchamp and Childress,Reference Beauchamp and Childress 5 informed consent requires the adequate disclosure of relevant information that patients need for their decision making. With regards to epigenetic risks associated with ART, we could reasonably presume that prospective parents would like to know those risks pertaining to their future child’s health. If such risks materialize into an imprinting syndrome or an adult-onset disease, it is the parents who would have to cope with their implications. This provides strong justification in favor of disclosure of such risks. Furthermore, Dickens and CookReference Dickens and Cook 48 argue that adequate informed consent should include information regarding possible alternative treatments, success rates, risks and side-effects of all possible treatments, and the possible uncertainty regarding those treatments. This highlights the importance of discussing with prospective parents the epigenetic risks associated with the different steps of ART, and the possibility of using a method that involves less risk (such as artificial insemination).
At the same time, clinicians should keep in mind that the provision of too much information could be overwhelming for prospective parents, and could lead to unnecessary anxiety. In addition, misunderstanding the information could impair prospective parents’ ability to make an informed decision.Reference Beauchamp and Childress 5 The way in which uncertainty is communicated plays an important role in patients’ satisfaction regarding their medical decisions.Reference Johnson, Levenkron, Suchman and Manchester 49 Educational campaigns can arguably help patients make better informed decisions about ART, even if information about epigenetic risks may cause anxiety. A study conducted in a fertility clinic in the United States showed that, when informed about the risk of multiple pregnancies, patients were more likely to choose single embryo transfer.Reference Ryan, Sparks and Sipe 50 With regard to the epigenetic risks associated with ART, educational resources should be developed. As this information involves risks and uncertainty, we argue that professional societies should consider how to guide their members in this matter, keeping in mind that paternalistic attitudes should be avoided and that prospective parents should have the autonomy to make their decisions with all the relevant facts in hand.
The ethical tension that arises from the possible conflict between the duty to respect prospective parents’ reproductive autonomy and the duty to protect the future child from epigenetic harm may be addressed – and to some extent resolved – by understanding ‘autonomy’ not merely as a right to choose freely, but also as a right and a responsibility to make informed choices. In fact, considering respect for autonomy as generating a duty to inform prospective parents implicitly promotes the notion of shared responsibility for the protection of the future child’s interests, thus pointing to the need to discuss pre-conception, as well as post-conception epigenetic risks. Importantly, the NIP does not diminish health professionals’ responsibility to inform prospective parents about the epigenetic risks associated with ART. Although the NIP suggests a difference in terms of moral sensitivity between identity-preserving (i.e. manipulations after fertilization) and identity-altering (i.e. manipulations before fertilization) interventions, we should keep in mind that, ultimately, parents might remain the best judges of the best interests of their child and the ethical acceptability of a procedure in their specific situation.
Conclusion
Beyond their implications for health professionals’ responsibilities, epigenetic risks associated with ART also have implications for research and policy. In the face of scant evidence about such risks in humans, future research should focus on assessing this risk for individuals conceived by ART. The implementation of registries of ART-conceived individuals in all countries, to ensure the collection of epidemiological data, or making such already existing registries mandatory, could help document the risk of the different ART for prospective children.Reference Feuer and Rinaudo 51 Over time, this could provide the required evidence base that would allow regulators, professional societies and individual clinicians to better address the needs and concerns of prospective parents and to improve the risk communication process. At the same time, further research on animals is important to understand the underlying epigenetic mechanisms involved in ART and is thus very valuable.Reference Feuer and Rinaudo 51 Moreover, research should focus on the ways in which epigenetic risks associated with ART could be reduced and on ways to reduce the consequences of such risks. For instance, research has already shown that promoting single pregnancies over multiples could reduce the epigenetic risks for metabolic programming.
In the meantime, guidelines should be developed by professional societies, informed by the experiences of patients undergoing ART treatments, to help health professionals communicate the epigenetic risks associated with ART to prospective parents. These guidelines could help them determine what specific information they should disclose to their patients in order to enhance patients’ capacity for informed decision making, and, consequently, their reproductive autonomy. Guidelines should address aspects such as how to define the concept of ‘epigenetic risk,’ how to convey uncertainty regarding such risk while avoiding inducing unnecessary anxiety, what degree of importance should be granted to animal studies when communicating ART-associated risks to prospective parents and how to assess on an ongoing basis the robustness of the emerging evidence in the literature (e.g. how to balance the results of studies suggesting that ART could be associated with imprinting defects against cohort studies that fail to confirm this hypothesisReference Lidegaard, Pinborg and Andersen 42 – Reference Bowdin, Allen and Kirby 44 ).
Finally, ART may sometimes represent a lower risk for the health of the future child than coital conception, as it seems to be the case for some parents carrying a defective gene. As evidence emerges, the less-risky ART alternatives should be promoted. For example, the use of ICSI could be restricted to cases of male-factor infertility.Reference Feuer and Rinaudo 51 Prospective parents could also consider attempting artificial insemination before undergoing IVF and, when possible, ovarian stimulation and in vitro maturation of gametes should be avoided. When establishing such a process for an ‘ethical prioritization of ART,’ however, it may be difficult for health professionals to inform parents without at the same time sounding like shaming them for their reproductive choices – which may be limited by the type of or reason for infertility. Indeed, it is crucial not to stigmatize people who need ART to conceive. Nevertheless, as evidence of ART-associated epigenetic risk increases, it will be important to promote public education to enable individuals to make better informed reproductive choices when they consider the use of ART.
Acknowledgments
The authors wish to thank Dr Marc-André Sirard for the invitation to participate in this special issue. The authors also thank Stanislav Birko for his helpful comments and Tierry Morel-Laforce for his assistance with some references. The authors also wish to thank the anonymous reviewer for the helpful comments.
Financial Support
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Conflicts of Interest
None.
