Earlier this month, members of parliament in the House of Commons voted to approve a new type of in vitro fertilization (IVF) which would allow the creation of so-called “three-person babies” in the United Kingdom. Although opponents attempted to block the plan, the House of Lords rejected these efforts last night and the legislation passed by a majority of 232. The U.K. is therefore now officially the first country to legalize the procedure.
The newly approved technique, which is called mitochondrial replacement therapy, or simply mitochondrial donation, aims to prevent the transmission of mitochondrial diseases from a mother to her child by removing faulty mitochondria and exchanging them for healthy versions from a donor. The result is a child whose DNA primarily comes from two parents, but 0.1% will come from a second woman.
Mitochondria are sausage-shaped structures, or organelles, found in our cells which serve as powerhouses. They produce energy in the form of a molecule called ATP, the so-called energy currency of life. Not only do these microscopic factories replicate independently of normal cell division, but they also have their own small genome, a vestige of their previous life as an ancient bacterium that was swallowed by a primitive cell early in the history of life.
Mitochondria only possess 37 genes, which is a considerably smaller number than the 30,000 odd that have been identified in our chromosomes. Unfortunately, mitochondrial DNA is more prone to mutation than the rest of our genome, and since these organelles are so critical to energy production and cellular function, the diseases which result from these faults are often devastating. They primarily target energy-hungry tissues, such as the brain, heart and muscles, and while severity varies, they are generally severely debilitating and some are fatal.
Since the few mitochondria which exist in sperm cells are destroyed shortly after fertilization, mitochondrial diseases are only passed down from the mother, whose egg cells are crammed with these organelles. To prevent these faulty factories from being transmitted to offspring, scientists developed a technique to remove a mother’s genetic material from her egg and transfer it to a donor egg without the disease-causing mitochondrial mutations. This egg then undergoes IVF and is implanted into the mother, ultimately resulting in a child whose nuclear DNA comes from two parents, but mitochondrial DNA comes from a different woman.
According to the BBC, it’s estimated that around 150 couples in the U.K. could be eligible for this procedure each year, and that babies could be born from it as soon as next year. But first, the U.K.’s fertility regulator will have to decide how best to license it.
Although the technique has the potential to help many families and has undergone three rigorous safety reviews, it has still been met with strong opposition from some. Religious groups argue it is unsafe and unethical, while others believe it is the first step along a slippery path towards designer babies.
At the moment, it is uncertain as to whether mitochondrial donation will be approved in the U.S. any time soon, although according to Science, the FDA has requested the Institute of Medicine to investigate the safety and ethical issues surrounding the procedure, and we should hear more soon.