Modern reproductive medicine has reached a significant milestone. Thanks to a groundbreaking technique known as Mitochondrial Replacement Therapy (MRT), eight healthy babies have been born in the United Kingdom, free from inherited mitochondrial diseases.
What Are Mitochondrial Diseases?
Mitochondria—the "powerhouses" of the cell—contain unique DNA (mtDNA), which is passed exclusively from mother to child. Mutations in mtDNA can cause severe multisystem disorders such as Leigh syndrome, MELAS, or mitochondrial cardiomyopathy. These diseases affect approximately 1 in every 5,000 births globally, and currently, there is no curative treatment.
How Does MRT Work?
The aim of MRT is to replace faulty mitochondria with healthy ones, without altering the nuclear genetic material from the parents. The process involves:
- Extracting nuclear DNA from the mother.
- Transferring this DNA into a donor egg that has had its nucleus removed but retains healthy mtDNA.
- Fertilizing the egg with the biological father's sperm.
- Implanting the resulting embryo into the mother's uterus.
The outcome is a child with nuclear DNA from both biological parents and only mtDNA (approximately 0.1%) from the donor.
Clinical Results in the UK (2025)
According to the latest data published by the Human Fertilisation and Embryology Authority (HFEA, July 2025):
- Eight children have been born using MRT at a specialized center in Newcastle, UK.
- In six cases, the proportion of the mother’s mutated mtDNA was below 5%, significantly under the threshold for disease manifestation.
- Pregnancy success rates after MRT were approximately 36%, consistent with standard IVF outcomes using preimplantation genetic diagnosis.
Why Is the mtDNA Proportion Important?
Scientific studies (Tachibana et al., Nature, 2009; Zhang et al., Reproductive Biomed Online, 2016) have shown that if the proportion of mutated mtDNA remains below 30%, the risk of disease symptoms is dramatically reduced. MRT therefore allows for a reduction in mitochondrial heteroplasmy—the coexistence of multiple types of mtDNA in a single cell.
Advantages and Current Developments
- MRT allows women with severe mtDNA mutations to have children who are genetically related to them..
- The technique has the potential to prevent thousands of cases of inherited diseases every year.
- MRT programs are currently expanding in Australia and Japan. Research is also underway in the United States, although clinical use remains pending.