From parents’ genetic disorders can be passed to offspring. This is the risk parents face when they plan on having babies. To prevent passing genetic disorders researchers at UK performed an IVF procedure which involved transfer of mitochondrial DNA or also known as Mitochondrial donation treatment MDT and therapy is called mitochondrial replacement therapy MRT.

Doctors at Newcastle Fertility Center in UK aimed to help women with mutated mitochondria to have healthy babies without genetic disorders.

HFEA: Mitochondrial donation treatment can be used by people with severe mitochondrial disease to avoid passing the condition onto their children.

Mitochondria which are known as powerhouse of the cell help in producing ATP which is source of energy for the body. Mitochondria being an organelle inside the cell contains its own DNAs or genes. Certain mutation in mitochondrial DNA has impact on energy supply and affects brain, heart, liver and muscles. Humans inherit mitochondria from their mother. If a woman has any such disorder in her mitochondrial gene, it could pass onto offspring leading to severe and progressive diseases. If the baby inherits a very small or tiny proportion of the mutated mitochondria, then baby might born healthy.

To prevent such diseases in future generation, UK researchers used Mitochondrial donation treatment. In this treatment the tissue from eggs of healthy women donors is used to create embryos by IVF method. Mitochondria of these women will be screened before proceeding with procedure. During IVF procedure donor nuclear material will be removed and destroyed and parents’ nuclear material will be placed inside donor egg where only the healthy donor mitochondria will be present. Fetus that develops will have DNA from both parents (99.8%) as well as a smaller portion of mitochondrial DNA that is, about 37 genes from the donor. Because of presence of three types of DNA in babies it is termed as “three-people babies”.

Newcastle clinic is the first and only center licensed to perform the procedure in UK. According to the reports, there are more than one babies born using this procedure that is approved by UK’s Human Fertilization and Embryology Authority – HFEA. How many babies are born is still not revealed to the press due to patients’ confidentiality. In 2016 Dr. John Zhang from New Hope Fertility Center of New York, attempted the mitochondrial transfer to get healthy baby in a couple. This was done in Mexico under the care of US fertility specialists. They had chosen Mexico because there was no rule and regulation in Mexico where as in US regulations were in place to do such IVF procedures. Out of five embryos doctors created, only one developed normally. In UK parliament changed the law in 2015 to permit MDT procedure and New Castle hospital is the first and only place MDT procedure is performed.

Peter Thompson, chief executive at the HFEA, said: “MDT offers families with severe inherited mitochondrial illness the possibility of a healthy child. The UK was the first country in the world to allow MDT within a regulatory environment … These are still early days for MDT and the HFEA continues to review clinical and scientific developments.”

General steps involved in the procedure are:

• Sperms from father is taken and used for fertilization of both mother egg and healthy donor egg.
• The nuclear material from donor’s egg is then removed
• After fertilization of parents’ egg, fertilized egg is transferred to donor’s egg.
• Donor’s egg will now have nuclear chromosomes of parents and mitochondrial DNA from donor.
• Healthy egg is implanted in donor’s womb.

Mitochondrial donation treatment:

There are two techniques involved in MDT – Maternal spindle transfer or MST and Pronuclear transfer PNT. In both eggs are created using nuclear genetic material and healthy donor mitochondria. In MST mother’s genetic material is removed from egg and transferred to donor eggs which will have previously nuclear genetic removed. These eggs are later fertilized with sperms to form embryos.

In PNT eggs are fertilized with sperms to create embryos. From the embryos nuclear genetic material is removed and transferred into embryos created by donor eggs and sperms. The original nuclear genetic material is removed from donor embryos, only healthy mitochondria is retained.  

Risk factors: Sometimes the tiny portion of mitochondria inevitably carried along with mother’s egg showed multiplication in donors’ womb. This is named as reversion. Reversion could lead to similar genetic disorder as mother. What is the solution: Those women who have mitochondrial gene mutation can screen the IVF embryos for such mutations. Or can go with IVF procedure using donor egg itself.

This research was commenced few years ago, however recent COVID-19 pandemic caused delay in the research as donors were not coming forward for obvious reason. Mitochondrial donor will not have any rights on the child born as the DNA that is used is less than 1%.

As for as future research – more studies or prenatal testing and long-term observation of children born with this technique is needed. It is essential to observe baby’s growth, development and activities. This will also help to understand if there is any reversal occurred by mitochondrial genes of mother.

References:

https://www.hfea.gov.uk/media/2611/fourth_scientific_review_mitochondria_2016.pdf

https://www.bbc.com/news/

https://www.nature.com/

https://www.newscientist.com/

https://www.hfea.gov.uk/ (for more images and articles)

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