Are We Finally Saying Goodbye to Inherited Mitochondrial Diseases? (Part 1)
Every parent wants their child to grow up healthy and strong, and live a long, happy life. However, that wish can’t always be fulfilled, and sometimes gets extinguished before the child is even born, due to inherited diseases. And among them, there’s a particularly insidious category: mitochondrial diseases. Passed down maternally and sometimes lethal, this disease disrupts cellular energy production and is quite common, effecting roughly 1 in every 5000 individuals.
But with huge advancements in medical science in recent years, we may finally be bidding farewell to inherited mitochondrial diseases, thanks to a procedure known as pronuclear transfer (PNT), a type of Mitochondrial Replacement Therapy (MRT). Just recently, this procedure led to the successful birth of 8 healthy infants in the United Kingdom, children who otherwise may have inherited mitochondrial illnesses. However, the treatment is still very controversial and has been regulated strictly even in countries pioneering MRT research.
In this two-part series, we’ll be examining mitochondrial diseases, the different types of MRT that attempt to mitigate the effects of those diseases, and the ethical and regulatory side of it all.
About Mitochondrial Diseases
Unlike most other inherited diseases, this type of disease doesn’t follow the rules of Mendelian inheritance. This is because it effects the mitochondria (also known as ‘the powerhouse of the cell’ due to its role in generating roughly 90% of all cellular energy), which contain their own DNA separate of a cell’s nucleus (mtDNA) and hence have different inheritance principles (inherited exclusively from the mother). Found in all cells in a human except red blood cells (which don’t have a nucleus either and are disk-shaped to better suit its purpose of carrying oxygen and carbon dioxide to and from the lungs), mitochondria converts the energy of food molecules into ATP (adenosine triphosphate), which then powers almost all biological processes.
So unsurprisingly, impaired mitochondria can have devastating effects, as it will severely disrupt ATP production and lead to energy deficiency. In addition, mitochondrial diseases could lead to multi-system failure, as it will effect virtually every organ and tissue throughout the body.
Types of MRT
Before we look at the different variations of MRT, I should point out that the treatment is only effective on inherited mitochondrial diseases; it can’t cure genetic mutations of mitochondria later in life, as MRT procedures are done before birth. In addition, the following types of MRT all rely partially on in vitro fertilization (involving removing an egg from a woman, collecting sperm from a man, fertilizing the sperm and egg, forming a blastocyst, and then transferring the blastocyst into the uterus), though MRT involves the extra step of collecting an egg from a third person (the donor) and manipulating both the mother’s and the donor’s egg.
With all that out of the way, let’s examine the first type of MRT developed - cytoplasmic transfer (CT), which was introduced in the late 1990s and pioneered at clinics such as St. Barnabas Institute in New Jersey. This procedure involved injecting the mother’s egg with cytoplasm from a donor egg, which would ‘boost’ embryo viability (as the donor’s cytoplasm would contain healthy mitochondria). Reportedly, over 30 babies were born as a result of this procedure, though the practice was later halted due to FDA concerns about genetic modification. However, cytoplasmic transfer had a major drawback; it only introduced some donor mitochondria, not a full replacement, leading to children with heteroplasmy (two types of mtDNA).
Conclusion
So how will that problem be solved in future MRT variations? That question - and the additional 3 types of MRT - will be explained in the next article of this series.
Thank you for reading. If you liked today’s article, please consider liking, subscribing, and sharing. Don’t forget to come back next week for Part 2.