How Three People Can Make a Baby - and Why It Matters
Last night, I had intriguing conversations with biotech scientists and a journalist at the DeSci event. Among topics like cultivated meat, blood transfusion, and reproductive technology, what fascinated me most was a baby with DNA from three people.
The basic idea is to use two eggs—one from the mother and one from the donor—remove the nucleus from the donor’s egg, inject the mother’s nucleus into it, and then fertilize it with the father’s sperm. At first, this seemed confusing to me—if the genome is stored in the nucleus, how could the embryo contain DNA from three people?
Curious to learn more, I looked into it when I got home. I found that the BBC reported in 2023 that a baby has been born using the DNA of three people for the first time in the UK. However, this wasn’t a groundbreaking first—the first known case was actually reported in 2016.
Initially, I thought this was another crazy trend, but this technology, mitochondrial donation treatment, is actually an attempt to prevent children from being born with devastating mitochondrial diseases. These incurable diseases can be fatal within hours or days of birth. For some families, like the woman who tragically lost seven children to mitochondrial disease, this technique offers hope for a healthy child.
To address this issue, scientists developed a specialized form of in vitro fertilization (IVF). The goal is to replace faulty mitochondria in a mother’s egg with healthy mitochondria from a donor.
The most commonly used method for mitochondrial donation is maternal spindle transfer, which repairs the egg before fertilization.1 Scientists first retrieve an egg from the mother, which contains faulty mitochondria, and carefully extract its nucleus. They then take a healthy donor egg, remove its nucleus, and discard it, leaving behind only the donor’s mitochondria. Finally, the mother’s nucleus is inserted into the enucleated donor egg, creating a reconstructed egg with her nuclear genetic material but healthy mitochondria. This egg is then fertilized with the father’s sperm, resulting in an embryo free from mitochondrial disease.
But what does this mean for the baby’s DNA—does it truly come from three people?
The answer lies in mitochondrial DNA (mtDNA), which actually makes up about 0.1% of our genome. While nearly all genetic material comes from the parents, mitochondria contain their own small set of DNA, inherited exclusively from the mother. When a donor provides healthy mitochondria, the baby inherits this tiny fraction (~0.1%) of DNA from a third person. However, since mitochondrial DNA only affects cellular energy production, it does not influence traits like appearance, personality, or intelligence. In essence, the donor’s contribution is solely to ensure the baby’s mitochondria function properly, preventing disease while leaving everything else unchanged.
Mitochondrial diseases are passed down only by the mother.↩︎