Three-Parent Babies: UK’s Groundbreaking Mitochondrial Therapy Explained
- Nidhi Santosh
- Aug 24, 2025
- 3 min read
-The ever advancing science of reproductive genetic engineering will blow your mind
I’m sure we all remember our first biology class on reproduction back in 8th grade—awkward teenagers, too shy to meet the teacher's gaze, stifling giggles. It was then that we learnt that reproduction involves a simple union: one sperm and one egg, each parent contributing 23 chromosomes. We have continued to carry this knowledge with us ever since. Yet, what if I told you that this isn't always the case?
As of July 2025, the Newcastle Fertility Centre reported the birth of eight children using pronuclear transfer technology, with another pregnancy underway. This groundbreaking IVF technique combines DNA from three individuals. Mind blowing right? This method is a type of mitochondrial replacement therapy and aims to prevent the transmission of severe mitochondrial diseases, offering new hope to families at risk.
The mitochondria are intracellular organelles, and just like the cell nucleus they have their own genome. They are extremely important for normal body functioning and are responsible for ATP production - the main energy source for the cell. Mitochondrial diseases are associated with mutations in mitochondrial DNA (mtDNA)and are inherited exclusively from the mother.
What is Pronuclear transfer (PNT)?
After the fertilisation of the mother’s egg with the father’s sperm, two pronuclei (PN) with defined membranes each containing a haploid (23) set of chromosomes become visible and migrate to the centre of the zygote.
In the PNT, the two pronuclei are removed from the zygote with mutated mitochondria and transferred to a normal healthy zygote that had their pronuclei previously removed. This creates a fertilised egg with a full set of chromosomes from the parents, but healthy mitochondria from the donor. The egg is then implanted into the womb to establish a pregnancy.
This technique is especially useful for women with homoplasmy (where all mtDNA copies are identical in a cell therefore all offspring will be affected) and high levels of heteroplasmy (due to the difficulty of selecting embryos with lower mutation load)
Let’s learn a bit more about mitochondrial diseases and the need for mitochondrial replacement therapy:
About one in 5,000 new-borns are affected with mitochondrial diseases. Mitochondrial diseases are mostly associated with mutations in mitochondrial DNA and are inherited exclusively from the mother. MtDNA mutations occur at a much higher rate than nuclear DNA (nDNA), which can be due to three factors: generation of oxygen radicals by the respiratory chain, the absence of histones to protect DNA and the presence of fewer repair systems.
Because muscle and nerve cells have especially high energy needs, muscular and neurological problems are common features of mitochondrial disorders. Other common symptoms include impaired vision, hearing loss, abnormal heartbeat (cardiac arrhythmia), diabetes, and stunted growth and other various incurable diseases. Mitochondrial disorders that mostly cause muscular problems are called mitochondrial myopathies while mitochondrial disorders that cause both muscular and neurological problems are called mitochondrial encephalomyopathies (encephalo refers to the brain). Many affected children have developmental delays, require wheelchairs, and die young.
Some common mitochondrial diseases are: Mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome, Leigh syndrome, Leber hereditary optic neuropathy (LHON), etc. Health conditions such as Type 1 diabetes, cancer, multiple sclerosis, and Alzheimer’s disease can also lead to secondary mitochondrial disease, which is not inheritable and cannot be passed on to a child.
CONCLUSION
The successful use of Pronuclear technology in 8 UK babies means life without mitochondrial disease for those children — a historic medical breakthrough in reproductive genetics, and a real sign of progress in fighting previously untreatable inherited diseases. However, mitochondrial replacement therapy (MRT) is not without ethical concerns. Issues such as the legal and moral status of the mitochondrial donor, the unknown long-term health risks the children may face and the fact that donated mitochondrial DNA is passed on to future generations — effectively altering the human germline — continue to spark debate.
Nevertheless, it is important to recognize the profound impact of this technology. Mitochondrial replacement techniques offer women with faulty mitochondria a new and hopeful path to having healthy biological children. For many families, it is not just a scientific advancement — it is a life-changing opportunity.
REFERENCES
Farnezi HCM, Goulart ACX, Santos AD, Ramos MG, Penna MLF. Three-parent babies: Mitochondrial replacement therapies. JBRA Assist Reprod. 2020 May 1;24(2):189-196. doi: 10.5935/1518-0557.20190086. PMID: 32073245; PMCID: PMC7169912. https://pmc.ncbi.nlm.nih.gov/articles/PMC7169912/
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