Mitochondrial replacement therapy (MRT) is a relatively new fertility technique which enables couples, who are at risk of passing on a mitochondrial disease, to have a healthy baby. A female egg contains the main DNA, found in the nucleus, and mitochondrial DNA (mtDNA). The mtDNA makes up under 0.001% of the cell’s total genetic content and contains genes involved in making energy for the cell. One method of MRT, pronuclear transfer, involves taking the fertilised egg from the mother and father, removing the nucleus and placing it in a donor egg cell with healthy mtDNA, which has had its own nucleus removed – hence, the ‘three-parent’ aspect (the diagram below explains it a bit better…). In 2015, the UK Parliament made the ground-breaking move of being the first country in the world to legalise pronuclear transfer.
However, the clinical success of MRT has reached its first big milestone; on 27th September 2016, New Scientist announced that John Zhang, from the New Hope Fertility Centre in New York, had successfully used MRT to produce the first ever living healthy birth using the technology (called Baby X here as the name has not been released). However, the Muslim couple involved objected to the destruction of embryos, which is often an unfortunate repercussion of pronuclear transfer, so they opted for a different method of MRT called maternal spindle transfer (again, the diagram below explains it well). The mother in this trial was healthy herself, but she was found to carry genes for the fatal mitochondrial disorder, Leigh syndrome, and after previously losing two previous children to said disorder, the parents opted to volunteer to be a part of the MRT trial.
Theoretically this technique should work with any mitochondrial disease with a known mutation on the mtDNA. Mitochondrial disorders are normally fatal with debilitating symptoms, so it is exciting to think that there is a realistic way of bringing hope to families who have such conditions. As well as helping patients, it also gives hope for the future of genetically-modified IVF. If IVF can be successful with the alteration of mtDNA, it may be indicative that IVF would still be successful if the normal DNA was modified. Doing so would allow the eradication of many known genetic disorders caused by mutations on the chromosomes, rather than just the mitochondrial genes.
However, such technology obviously comes with huge ethical repercussions. For example, many are against the genetic manipulation of germ-line cells or embryos – a necessary component of MRT. Another big issue is the involvement of a ‘third parent’; although the actual DNA contribution of the donor is extremely minimal and has no effect on the physical appearance of the resultant child, many are uncomfortable with the social and mental problems it could leave with the child. Some argue that the stigma of a third parent may be mentally distressing for the child, and even some suggest that the third parent should be stated as a biological parent on the birth certificate as they have some form of genetic contribution, no matter how small.
My personal view is that MRT is an excellent development in the field of genetics. Clearly it has many ethical issues, as do many new scientific technologies, and I do believe it should be researched for a greater length of time before any more children are born using the method; however, ultimately I think that it is so exciting that we have the technology available to improve the lives of so many people and eradicate some dreadful diseases from families and this should be celebrated as a scientific feat.
https://www.newscientist.com/article/2107219-exclusive-worlds-first-baby-born-with-new-3-parent-technique/ (Exclusive article from Baby X’s birth)
http://www.fertstert.org/article/S0015-0282(16)62670-5/fulltext?rss=yes (Zhang et al.‘s original article stating their results)
http://nyscf.org/pdfs2/FAQ_on_Mitochondrial_Replacement_Therapy.pdf (More in-depth information on MRT)