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expert reaction to news reports of first baby born using mitochondrial replacement therapy

There have been news reports that babies have been born in the UK following mitochondrial replacement therapy (MRT).


Dr David Clancy, Lecturer in Biogerontology, Lancaster University, said:

“The ethical and procedural facets of this whole area are many and fascinating. This is partly due to differing perspectives and the different languages that they use. Medical doctors may be medical scientists but first they are medical doctors who see actual patients with actual conditions and actual suffering, and this affects the language they use. During the (in my opinion) particularly unedifying and uneducated parliamentary debate on MRT, a lot of language was used in terms of cure. Mitochondrial replacement therapy is not really even therapy, and it is certainly not a cure in any regular sense of the word.

“However, it is good to know the technique has met with success, though we don’t know many details. Certainly until part way through 2019 there had been no successful pregnancies from 17 attempts (separate FoI request). As was predicted and as has happened with IVF, it is likely that the technique has become refined over time such that the likelihood of successful pregnancy has increased.

“Scientists look at the biology and their language is different: mito-nuclear interactions, mitochondrial carryover and clonal expansion. What we don’t know yet is whether mitochondria carrying the disease mutation have being carried across with the fertilised nucleus into the donor eggs, nor whether this will result in a child who both suffers from mitochondrial disease and is a carrier of affected mitochondria. Still no other country has approved this process, some (US and others) because they consider it to be germline modification. There was consideration that only male offspring should be created by this process because males cannot pass on mitochondria and therefore cannot pass the disease onto any offspring of their own. I don’t think it was a requirement in the HFEA approval. Nor do I know the extent to which women who carry mitochondria which cause disease are informed of the options to have a child by donor egg, because mitochondrial replacement is a technique whose only advantage is to allow a woman to have a child that is genetically related to her.”


Prof Darren Griffin, Professor of Genetics, University of Kent, said:

“With all medical procedures there is an assessment of risk vs benefit to be performed.  In the case of MDT/MRT, it undoubtedly raises interesting and challenging ethical questions. In this case however these need to be balanced against the prospect of these families having children with severe and life-threatening diseases. Media-constructed phrases like “three parent babies” do not really help the debate. Here, the research is not new, the initial findings have been published and it was already established that the Newcastle group are world-leading in this regard. The news, through a freedom of information request, is that it has been established what we already assumed that there have been babies born through this procedure. My best wishes to these families who we hope have now been able to have children unaffected these diseases.”


Prof Robin Lovell-Badge FRS FMedSci, Group Leader, Francis Crick Institute, said:

“While knowing that babies have been born in the UK following the use of mitochondrial replacement techniques is newsworthy, especially as this is being done in an appropriately regulated environment, scientists, clinicians and patients will want to see the details. I am sure that these will be made available, probably in a peer-reviewed scientific publication and hopefully in the near future. The Newcastle team involved in carrying out the procedures are cautious and will have wanted to include at least some follow-up data on the babies, while also protecting the privacy of the families. This is a challenge in itself. It will be interesting to know how well the MRT technique worked at a practical level, whether the babies are free of mitochondrial disease, and whether there is any risk of them developing problems later in life or, if female, if their offspring are at risk of having the disease. Such problems might arise if there is ‘reversion’, where the initially small amounts of the mother’s mitochondrial DNA, with the disease-causing variant gene, that are carried over with her nuclear DNA, are amplified*. The Newcastle team were aware of the fairly low chance of this happening before the clinical application of the techniques, but without MRT being used, the risks of the children having mitochondrial disease would be very high. 

(*This was seen in a small number of cases in proof of principle experiments in cell culture and recently in one out of six children born after the use of MRT in attempts to treat infertility in women for whom IVF has failed repeatably (which is not a use permitted in the UK). The reasons for such reversion events are not yet understood, but developing methods to avoid them will be scientifically important and reassuring to the patients, children and to those performing the procedures, even if the risks of them happening, and of any adverse consequences, are fairly low.)”


Sarah Norcross, Director of PET, said:

“The UK was the first country to legislate for the clinical use of mitochondrial donation. The relevant law was passed only after many years of careful research, assessment and deliberation. Even then, it was decided that use of this technology would be permitted by the regulator only on a case-by-case basis.

“This measured approach was and is appropriate, given the relative novelty of this technology. News that a small number of babies with donated mitochondria have now been born in the UK is the next step, in what will probably remain a slow and cautious process of assessing and refining mitochondrial donation.

“The purpose of this technology is to give people a way of avoiding the transmission of debilitating mitochondrial disease to their children. Given the toll that such disease is likely to have taken on the first families who have made use of mitochondrial donation, it is especially important that the privacy of these families is respected.”


Peter Thompson, Chief Executive, HFEA, said:

“Mitochondrial donation treatment offers families with severe inherited mitochondrial illness the possibility of a healthy child. The UK was the first country in the world to allow mitochondrial donation treatment within a regulatory environment. The HFEA oversee a robust framework which ensures that mitochondrial donation is provided in a safe and ethical manner.  All applications for treatment are assessed on an individual basis against the tests set out in the law and only after independent advice from experts.  These are still early days for mitochondrial donation treatment and the HFEA continues to review clinical and scientific developments. More information can be found on the HFEA website. 



Declared interests

Dr David Clancy: “No DOIs.”

Prof Darren Griffin: “No COI.

Prof Robin Lovell-Badge: “no financial conflicts of interest and I do not work on MRT. However, I have served on committees for the HFEA examining the likely safety and efficacy of MRT, and I am currently a member of the HFEA’s Scientific and Clinical Advances Advisory Committee, which will probably consider MRT again once there is published data.”

Sarah Norcross: PET – – is a charity which improves choices for people affected by infertility and genetic conditions.

For all other experts, no reply to our request for DOIs was received.

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