While the concept of 3-parent babies may seem weird and confusing at first, medical advancements have made 3-parent babies a reality, thus preventing the transmission of certain genetic diseases. In order to explain how this works, we must first examine the biology behind it.
Your DNA has between 20,000-25,000 genes which are arranged in chromosomes. While one would expect half of your genes to come from your mother and half to come from your father, in actual fact, slightly over half come from your mother. This is because your mitochondria contain DNA and you only inherit mitochondria from your mother! As such, these 37 mitochondrial genes are just received from your mum. This is called maternal inheritance. Indeed, maternal inheritance is the main way that genetic history sites track your maternal lineage, as mitochondrial DNA is passed down from daughter to daughter virtually unchanged.
The reason behind maternal inheritance is still unclear. To date, the most convincing theory is that the paternal mitochondria in the sperm cell have a self-destruct mechanism (caused by a gene called cps-6) which is triggered during fertilisation (when the sperm cell fuses with the unfertilised ovum). Without this self-destruct mechanism, the embryo would have a lower chance of survival.
One theory as to why the embryo would have a lower chance of survival is because sperm cells generate lots of energy while swimming up the oviduct to fertilise the ovum. As such, they become overworked which could lead to DNA mutations in the mitochondria.
Mitochondrial disease is a major problem that can lead to several other genetic conditions including blindness, nerve damage and dementia. Nevertheless, as I will explain in this article, mitochondrial transfer can be used to stop the inheritance of these conditions.
The theory behind mitochondrial transfer has been around for several decades, dating back to 1983. Indeed, there have been many other trials in the past attempted to solve the problem of mitochondrial disease. For example, in the 1990s, embryologist Jacques Cohen attempted to inject healthy mitochondria into eggs from woman who had undergone many rounds of unsuccessful IVF treatment (this method was called ooplasmic transfer). Nonetheless, due to fetuses developing other serious genetic disorders, this trial was aborted and the FDA instructed all fertility clinics to stop using this method.
In the last few years, however, mitochondrial transfer has been carried out by the process of spindle nuclear transfer. This process, developed by Dr Zhang, works by removing the nucleus from the mother's egg cell and then inserting it into a donor egg cell which has had its nucleus removed. As such, you now have an egg cell which contains both the mother's genes and healthy mitochondria. This hybrid egg cell is then fertilised with sperm from the father, forming an embryo. Lastly, the embryo is implanted into the mother's womb to mature normally.
Since this procedure was invented, several babies have been born with this technique. The first, in April 2016, was the son of a mother who carried a rare, incurable disease that causes severe neurodegeneration called Leigh's Syndrome. Nevertheless, the procedure resulted in the birth of a son who, according to Dr Zhang, did not have the neurological disease.
The procedure has also been used this year to allow infertile mothers to have children in Greece. On the 9th April, a boy was born to a mother who had a history of IVF failures. However, the mother had no history of mitochondrial disease. As such, there are concerns that this is not what this procedure was developed for.
There are, however several concerns with mitochondrial transfer, especially with regards to biological concerns. The biggest worry is that some faulty mitochondria will inevitably get transferred with the nucleus and be placed in the hybrid cell. As such, if these faulty mitochondria replicate faster than the healthy ones, they might cause a mitochondrial disorder later in life. Furthermore, there are also concerns that because there are 3 people's DNA in the egg cell, it may disturb the relationship between the nucleus and the mitochondria, creating all kinds of unforeseen problems.
Numerous safety concerns are also associated with mitochondrial transfer and the rapid unfolding of this new technology. This is most notable in the stark contrast between different countries in the regulation of this technology. While USA and UK heavily regulate these trials, countries such as Mexico and Ukraine have very little restrictions at all. This is why Dr Zhang choose to carry out his trial in Mexico instead of in the USA. As such, because researchers gravitate towards these countries, further research is at the risk of being unsafe.
The largest ethical concern with mitochondrial transfer is with the potential misuse of the procedure, resulting in so-called "designer babies". If this procedure is developed further, especially in countries with poor regulation records, we might find ourselves in a position where it is possible to genetically modify babies by choosing their genes, and thus their characteristics. Furthermore, if the child is a girl, then she will carry mitochondrial DNA from the donor which, if she has a daughter, could then be passed down along many generations to come.
In conclusion, I would suggest that while results are promising, it is too early to tell how safe or reliable this new method is, especially when considering that the first boy is only 3 years old. Furthermore, there are many legal and ethical concerns associated with 3-parent babies, the most noticeable being the possible development of "designer babies". As such, I contend that we are still several court cases away from having a sufficient legal framework in place to move this procedure into mainstream medicine. In addition, without strict guidelines and regulation in the countries where this research is being carried out, the scientific community runs the risk of damaging lives while the research is completed.
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