The science of mitochondrial donation

Mitochondrial donation involves replacing the mitochondria in a woman’s egg with mitochondria from another woman’s egg, in order to prevent the transmission of serious mitochondrial disease from mother to child.

Mitochondria are small structures that are located inside nearly every cell of the body. They are often referred to as the powerhouse of the cell as their primary role is to produce the energy that the cell needs to function.

Mitochondria contain their own small piece of DNA that is transmitted by from mother to child. Mutations within this mitochondrial DNA can lead to mitochondrial disease, which is not uncommon and can be devastating.

Mitochondrial disease can occur at any age, with a wide range of clinical symptoms typically more severe in infants and children.

Several organs or tissues can be affected but it is usually those with the highest energy demands, such as the brain, heart and muscles. Deafness, diabetes and epilepsy are examples of conditions that can result from mutations to mitochondrial DNA.

There is no cure for mitochondrial disease and the variability in genetic defects and disease severity makes it challenging to manage these types of diseases. This is why preventing transmission from a mother to a child is so important.

The process of separating the patient’s healthy nucleus from defective mitochondria, and fusing it with healthy mitochondria from the donor is shown in the below diagram.

The steps of mitochondrial donation

With mitochondrial donation, we can replace the mutated mitochondrial DNA from the mother’s egg with healthy mitochondrial DNA from a third-party donor.

This is done by removing the nucleus from a donor egg containing normal mitochondria and inserting the nucleus from the prospective mother’s egg instead. This is performed during IVF before the egg is fertilised but can also be performed just after fertilisation.

Dr Helen O’Neill is a scientist and a teaching fellow at UCL’s Institute for Women’s Health. In this interview, she explains why mitochondrial donation is such a useful technique, not just to avoid disease, but to help us understand the genetics that underlies human development.

For your discussion: Mitochondrial DNA makes up less than 0.2% of our body’s total DNA, yet that hasn’t stopped many people naming the outcome of this technique ‘three-parent embryos’. What do you think of this term?