Three Parent Babies Explained

Mitochondrial Replacement Therapy (MRT) is a breakthrough in genetic engineering that has allowed babies sharing the genetic information of three different parents to be born. MRT was made legal in the UK in 2015, and that decision has brought the possibility of genetically modified children to a whole new reality, as well as highlighting many of the ethical complications that arise from this ground-breaking science.

Why do we need MRT?
Mitochondria are found within every cell and their main role is to generate energy in the form of ATP. This is achieved through a very complicated chain of reactions which involves the transfer of electrons and pumping of hydrogen ions. This means that mitochondrial diseases mainly affect organs requiring large quantities of energy such as the brain and various muscles. A diagram of a mitochondrion can be seen below.

Unlike other organelles within a cell, a mitochondrion contains its own DNA (https://steemit.com/science/@ovij/what-is-dna-why-do-we-need-it), which contains 37 genes. Thus, mutations in these 37 genes can cause devastating diseases including Diabetes mellitus and Leigh syndrome. Due to the mechanisms of fertilisation of an egg and sperm cell, mitochondria are only inherited from the egg. As a result, mitochondrial diseases are always inherited from the mother (as seen in the pedigree diagram below). Furthermore, if a mother is affected with a mitochondrial disease then it will be passed on to all her children, because mitochondrial DNA is only inherited by the mother (as described above).

Mechanism of MRT
With MRT the diseased mitochondria from the mother are replaced with healthy mitochondria from a donor egg, thus removing the diseased mitochondrial DNA, rendering the baby healthy. A simplified mechanism for this procedure is to:

1. Fertilise the mother’s egg (containing unhealthy mitochondria), then remove the genetic material from this egg.
2. Fertilise a donor egg (containing healthy mitochondria) and remove and destroy the genetic material from this egg.
3. Place the genetic material from the mother’s egg into the donor egg.

Through this method, the offspring will have healthy mitochondria, not the diseased mitochondria from the mother and thus not have the disease. Babies born through this method are described as having three parents since they not only contain the DNA of their parents but also the mitochondrial DNA from the donor egg. There are actually a few methods used to undertake MRT, which include pronuclear transfer and spindle transfer. A summary of these techniques can be found here: https://www.sciencenews.org/article/three-parent-babies-explained.

MRT raises various ethical queries since the manipulation of the embryo will affect all the cells of the child, including its germ cells. This means any potential side effects of the treatment could be passed on to his or her offspring. Moreover, the possibility of genetically engineering offspring has suddenly become a reality. Do you think that MRT should be undertaken and be legal in the UK? How do you feel about the possibility of genetically engineering babies? Where would you draw the line?

References:
https://www.sciencenews.org/article/three-parent-babies-explained
https://www.theguardian.com/science/2016/dec/15/three-parent-embryos-regulator-gives-green-light-to-uk-clinics
http://ocw.tufts.edu/Content/51/lecturenotes/551169/551276