Two genetic mothers practice can genetically modify the germline and cause problems in offspring, by being genetically linked three people: two genetic mothers and a father.
On 3rd February 2015, the British House of Commons gave the green light to the possibility of using a technique called “mitochondrial transfer”, aimed at resolving the problem of women with mitochondrial diseases that can be transmitted to their children. This is what in the media has been called creating “babies with three genetic parents”.
This technique has undoubted ethical drawbacks that should be assessed
The aim of this technique is for children born to be unaffected by their mother’s mitochondrial defects. However this technique, which in principle seems very positive, has undoubted ethical drawbacks that should be assessed.
Mitochondrial are small organelles present in the cytoplasm of most cells. Their main function is to generate cell energy. Therefore, mutations in the DNA of the mitochondria (mtDNA) cause a lack of cell energy that can affect different organs, resulting in diseases that can become serious, and even lead to early death. These diseases affect approximately 1 in every 5000 newborns, while 1 in every 200 healthy individuals is a carrier of a pathological mitochondrial mutation, which could pass to their children and manifest itself as disease.
There is no effective treatment for these diseases at present, so medical research is aimed at developing techniques to prevent their transmission to offspring. Two new techniques have been developed in recent years: Maternal Spindle Transfer (MST) and Pronuclear Transfer (PNT). In PNT, two single cell embryos (zygotes) are produced in vitro, one from the egg of the mother with the abnormal mitochondria, and another from the egg of a donor with normal mitochondria. The nucleus is then extracted from the zygote of the woman with the chromosomal abnormality and transferred to the previously enucleated zygote of the healthy woman, thus producing a new zygote with normal mitochondria. This latter zygote can develop in vitro until it reaches an appropriate evolutionary stage for transfer to the uterus.
In MST, in contrast, the nucleus is extracted from the egg of the woman with the abnormal mitochondria and transferred to the previously enucleated egg of the woman with normal mitochondria. Thus, a new egg is obtained with normal mitochondria, which is then fertilised in vitro and transferred to the mother’s uterus.
No differences have been shown between the two techniques as regards safety and efficacy. However, PNT is ethically more controversial, due to the fact that it requires the destruction of two human embryos, which does not occur in MST. Nevertheless, both techniques raise objective ethical difficulties, so in June 2014, the Bioethics Observatory at the Catholic University of Valencia sent a report to the British Government highlighting these difficulties although, as expected, we have not yet received any reply.
This innovative technique raises two major ethical issues: the first is that the germline can be genetically modified, and the second is that it can cause problems in children born using this technique, by linking them genetically to three people (the two women who donate the eggs and the man who donates the sperm to fertilise the hybrid egg resulting from the mitochondrial transfer).
In relation to the first difficulty, genetic alteration of the germline, the most serious issue raised is whether changes are produced in the DNA of the gametes that could then be transferred to the children and future generations. Therefore, any technique that can modify the germline must be very rigorously evaluated.
With respect to this however, it is important to establish a difference between the DNA of the nucleus and that of the mitochondria, since the DNA of the latter (which is the DNA altered in the aforementioned technique) is essential for generating cell energy. Therefore in theory, its possible modification would not raise the same ethical problems as modification of the nuclear DNA, although it has not been clearly established whether modifications in mitochondrial DNA could affect the nuclear DNA. Consequently, given the uncertainty of these facts, ., although we do not know whether this has been taken into account by the British parliament.
We believe that all the above forces us to reflect on legislation, which for the first time ever gives a green light to mitochondrial transfer (in a developed country). While this legislation undoubtedly has positive aspects in the sense that it can prevent the transmission of mitochondrial diseases to children, it also presents the ethical difficulties mentioned above.
Lucia Gómez Tatay, José Miguel Hernández and Justo Aznar
Catholic University of Valencia