Authorities in the United Kingdom have given the go-ahead for mitochondrial replacement therapy, a new type of assisted reproduction that could allow some families to avoid passing on genetic disease. The technique is controversial because it combines genetic material from three people: two eggs and one sperm. The decision, announced today, has been widely anticipated. It comes after years of debate and a change in the country’s laws passed by Parliament in 2015.
Mitochondrial disease results from mutations in the DNA carried in a person’s mitochondria, cellular energy sources which carry their own set of genes. When mitchondria don’t work properly, a range of symptoms can result, including brain damage, blindness, seizures, and heart problems. Women who carry the mutations can pass them on to their children. (Although sperm have mitochondria, they typically degrade shortly after fertilization.)
For years, researchers have been working to develop ways to replace the faulty mitochondria in affected women’s egg cells. They have developed several methods that involve combining the nucleus from the egg of an affected woman—which carries the bulk of our DNA—with the cytoplasm from an unaffected woman, which contains the mitochondria. At least one baby has been born after the procedure, used by doctors working in Mexico.
The decision today by the Human Fertilisation and Embryology Authority allows clinics in the United Kingdom to apply for a license to treat patients with the technique. Researchers at Newcastle University in the United Kingdom have been at the forefront of the work, and they said they plan to apply for a license as soon as possible. Doug Turnbull, who has helped lead the research, said in a statement that he and his colleagues "will be aiming to treat up to 25 carefully selected patients a year with the mitochondrial donation technique as a clinical risk reduction treatment. We will also provide long-term follow up of any children born.”
Recent work has raised questions about how effective the current methods will be. Researchers working with eggs from affected women found that some of the defective mitochondria from the mother’s egg made it into the embryo along with the nuclear DNA. The scientists made embryonic stem (ES) cells from the embryos, and found that in some cases the faulty mitochondria became the predominant type in the ES cell lines. That suggests that even a few mutant mitochondria tagging along could end up causing disease in a child born using the technique.
In the United States, a National Academies of Sciences, Engineering, and Medicine panel recommended that the technique be allowed to go forward. However, Congress has prevented the Food and Drug Administration from approving any applications for using the technique in patients.