by Josh Forman, Head of Science, Education & Outreach
Some incredible news has just come out of Newcastle: eight babies have been born using a groundbreaking technique that’s actually been legal in the UK for almost a decade. This method involves using the biological parents’ sperm and nuclear DNA, but with an egg donated by a third person.
Colloquially, we call these children ‘three-parent babies’. Why? Because while most of our genetic material comes from our parents, half from each, found in the nucleus of our cells, there’s a second, often overlooked, type of DNA that lives in our mitochondria.
Mitochondria, often called the ‘powerhouse’ of the cell, have their own separate DNA. And unlike nuclear DNA, which comes from both parents, mitochondrial DNA (mtDNA) is inherited solely from the mother. That’s because the egg contributes almost all the cellular machinery to the embryo, including the mitochondria, while the sperm’s mitochondria are typically destroyed after fertilisation. So the mitochondrial DNA we all carry is inherited only from our maternal line.
*Fun fact: it’s widely believed that mitochondria were originally free-living organisms, millions of years ago, that formed a symbiotic relationship with primitive cells. Over time, they became essential organelles within our cells—but retained their own DNA.*
Why does this matter? Because mutations in mitochondrial DNA can lead to serious, often untreatable diseases. These mutations affect the mitochondria’s ability to function properly, which in turn disrupts the cell’s energy production. Because mitochondria are so crucial, even small changes can lead to severe health problems.
What makes this particularly challenging is that a mother might carry a mitochondrial mutation without showing symptoms herself. This is because the mutation may only affect some of her mitochondria, and these are distributed unevenly among her eggs. Some eggs may carry a high proportion of faulty mitochondria, while others don’t. If an egg with a high mutation load is used in reproduction, the resulting child may develop mitochondrial disease, even if the mother was unaffected or only suffered mild symptoms. In this case, all families involved in the project knew that they carried this risk because of previous children, family members or the mother involved suffering from a mitochondrial disease.
This is where this new technique comes in. To prevent passing on faulty mitochondria, scientists fertilise both the mother’s and the donor’s egg cells (similar to IVF). Then, when the embryos develop to a certain point, the nuclei are removed from both, and the DNA from the mother’s now fertilised egg is placed into the developed, fertilised donor egg. The result is an egg with healthy mitochondria and the parents’ nuclear DNA. This way, the embryo contains DNA from the mother and father, plus the mitochondrial DNA from the donor, the ‘third parent’.
At Jnetics, we’re all too familiar with the impact of mitochondrial disease. We screen for one such condition, Mitochondrial Complex I Deficiency, which can arise from mutations in either the mitochondrial or nuclear DNA. The form we test for is actually caused by a mutation in the nuclear DNA, since we don’t currently screen mitochondrial DNA.
We’ve engaged with this topic before: last year, we hosted a panel titled “Three-Parent Babies: We Can, But Should We?” featuring three world-leading experts, including Professor Joanna Poulton, who explained the science and ethical implications with brilliant clarity. You can watch it on our YouTube channel if you’re interested.
This latest news marks a historic milestone. For the first time, this technique has been successfully used in a clinical setting to help families have healthy children free from devastating mitochondrial diseases. It opens a new chapter in reproductive medicine, one where science gives us not just the power to create life, but to protect it from genetic harm.
