Ten years after the UK became the first country to legalise mitochondrial donation, the first results from the use of these high-profile reproductive technologies – designed to prevent passing on genetic disorders – have finally been published.

So far, eight children have been born, all reportedly healthy, thanks to the long-term efforts of scientists and doctors in Newcastle, England. Should this be a cause for excitement, disappointment or concern? Perhaps, I would suggest, it could be a bit of all three.

The New England Journal of Medicine has published two papers on a groundbreaking fertility treatment that could prevent devastating inherited diseases. The technique, called mitochondrial donation, was used to help 22 women who carry faulty genes that would otherwise pass serious genetic disorders – such as Leigh syndrome – to their children. These disorders affect the body’s ability to produce energy at the cellular level and can cause severe disability or death in babies.

The technique, developed by the Newcastle team, involves creating an embryo using DNA from three people: nuclear DNA from the intended mother and father, and healthy mitochondrial DNA from a donor egg. During the parliamentary debates leading up to The Human Fertilisation and Embryology (Mitochondrial Donation) Regulations in 2015, there were concerns about the effectiveness of the procedure and its potential side effects.

The announcement that this technology has led to the birth of eight apparently healthy children therefore marks a major scientific achievement for the UK, which has been widely praised by numerous scientists and patient support groups. However, these results should not detract from some important questions they also raise.

First, why has it taken so long for any updates on the application of this technology, including its outcomes and its limitations, to be made public? Especially given the significant public financial investment made into its development.

In a country positioning itself as a leader in the governance and practice of reproductive and genomic medicine, transparency should be a central principle. Transparency not only supports the progress of other research teams but also keeps the public and patients well informed.

Second, what is the significance of these results? While eight babies were born using this technology, this figure contrasts starkly with the predicted number of 150 babies per year likely to be born using the technique.

The Human Fertilisation and Embryology Authority, the UK regulator in this area, has approved 32 applications since 2017 when the Newcastle team obtained its licence, but the technique was used with only 22 of them, resulting in eight babies. Does this constitute sufficiently robust data to prove the effectiveness of the technology and was it worth the considerable efforts and investments over almost two decades of campaigning, debate and research?

As I wrote when this law was passed, officials should have been more realistic about how many people this treatment could actually help. By overestimating the number of patients who might benefit, they risked giving false hope to families who wouldn’t be eligible for the procedure.

The safety question

Third, is it safe enough? In two of the eight cases, the babies showed higher levels of maternal mitochondrial DNA, meaning the risk of developing a mitochondrial disorder cannot be ruled out. This potential for a “reversal” – where the faulty mitochondria reassert themselves – was also highlighted in a recent study conducted in Greece involving patients who used the technique to treat infertility problems.

As a result, the technology is no longer framed by the Newcastle team as a way to prevent the transmission of mitochondrial disorders, but rather to reduce the risk. But is the risk reduction enough to justify offering the technique to more patients? And what will the risk of reassertion mean for the children born through it and their parents, who may live with the continuing uncertainty that the condition could emerge later in life?

As some experts have suggested, it may be worth testing this technology on women who have fertility problems but don’t carry mitochondrial diseases. This would help doctors better understand the risks of the faulty mitochondria coming back, before using the technique only on women who could pass these serious genetic conditions to their children.

This leads to a fourth question. What has been the patient experience with this technology? It would be valuable to know how many people applied for mitochondrial donation, why some were not approved, and, among those 32 approved cases, why only 22 proceeded with treatment.

It also raises important questions about how patients who were either unable to access the technology, or for whom it was ultimately unsuccessful feel, particularly after investing significant time, effort and hope in the process. How do they come to terms with not having the healthy biological child they had been offered?

This is not to say we shouldn’t celebrate these births and what they represent for the UK in terms of scientific achievement. The birth of eight healthy children represents a genuine scientific breakthrough that families affected by mitochondrial diseases have waited decades to see. However, some important questions remain unanswered, and more evidence is needed and it should be communicated in a timely manner to make conclusions about the long-term use of the technology.

Breakthroughs come with responsibilities. If the UK wants to maintain its position as a leader in reproductive medicine, it must be more transparent about both the successes and limitations of this technology. The families still waiting to have the procedure – and those who may never receive it – deserve nothing less than complete honesty about what this treatment can and cannot deliver.

Cathy Herbrand receives funding from the Economic and Social Research Council.