The controversial new procedure to create “three-parent babies” could be approved and available by as early as next year. Researchers announced this possibility because they found evidence suggesting the procedure is safe and will result in healthy babies. But what is this procedure, and is it as safe as it seems?
Known formally as mitochondrial replacement therapy or pronuclear transfer, this technique was developed as a way to produce a healthy baby that lack the sick mitochondria of the mother. As the proverbial ‘powerhouse’ of the cell, the mitochondria have their own set of DNA, which is derived solely from females. Thus, when a woman’s mitochondria are damaged or diseased, the chances of passing on these organelles to the baby can be quite high.
When damaged or mutated, abnormal mitochondria can cause several health conditions. These involve organs and tissues that consume high levels of energy, such as skeletal muscles, the brain, and the eye. And because the mitochondria are integral component of many biochemical processes, mitochondria dysfunction leads to a variety of metabolic diseases.
To help mothers with mutated mitochondria to have healthy children, researchers discovered that they could replace the diseased organelle, so to speak. In mitochondria replacement therapy (MRT), doctors use in vitro fertilization (IVF) to fertilize a mother’s egg (containing the bad mitochondria) with her partner’s sperm. When the embryo is still an undivided cell, doctors remove the nuclei and transfer the embryo’s DNA into a donor embryo, which is missing the nucleus.
Through switching organelles, the goal is to end up with a donor embryo (with healthy mitochondria) that has the essential DNA from the IVF procedure. The mother’s egg that contains the bad mitochondria is left behind. In theory, this prevents the mother from passing on her mutated mitochondria copies to her offspring. Because the procedure requires an embryo from a healthy donor, it’s often called the “three-parent baby” technique.
In a recent article, researchers from the UK say the procedure works and is safe. The researchers screened 500 eggs from 64 donors to assess whether the technique negatively affected the health outcome of the embryos. The team found that, indeed, replacing the sick mitochondria with healthy ones didn’t seem to hinder the embryos’ development. Furthermore, the procedure dramatically decreased the passage of unhealthy mitochondria to the embryos.
“This study using normal human eggs is a major advance in our work towards preventing transmission of mitochondrial DNA disease. The key message is that we have found no evidence the technique is unsafe. Embryos created by this technique have all the characteristics to lead to a pregnancy,” said Doug Turnbull, director of the Center for Mitochondrial Research and co-study author.
But there’s more to the procedure that may conflict with Turnbull’s confidence. While the procedure is safe, it didn’t prevent transmission of the bad mitochondria perfectly. That is to say, during the pronuclear transfer to an “empty” donor embryo, some of the bad mitochondrial copies still made it over. Thus there is still a chance of passing on the mother’s mutated mitochondria to the baby.
The team said the faulty mitochondria are transmitted in less 2 percent of the time, which significantly decreases health risks for the baby. However, another study, published in May, argued that carryover of faulty mitochondria can multiply and eventually overcome the healthy donor’s mitochondria. This, they claim, is a pitfall of MRT that still hasn’t been addressed fully.
With more studies ongoing, the efficiency of MRT will hopefully increase. But right now, Turnbull and his team are moving toward seeking federal approval with the Human Fertilization and Embryology Authority (HFEA), which is the equivalent of the US Food and Drug Administration. If a license is granted for MRT, the procedure may be available to women as early as 2017.
“We are optimistic that the technique we have developed will offer affected women the possibility of reducing the risk of transmitting mitochondrial DNA disease to their children,” said Mary Herbert, professor at the Wellcome Trust Centre for Mitochondrial Research at Newcastle University, and senior study author.
Additional sources: BBC, Independent UK, Science News