A lowdown on the ‘three-parent babies’ debate
On February 3, MPs voted in favour of changing the law on a controversial IVF technique to create babies with ‘three parents’.
The new law will allow IVF clinics to replace an egg’s defective mitochondrial DNA with DNA from a healthy donor to prevent debilitating diseases, such as muscular dystrophy.
For many people who don’t have knowledge of mitochondria, the ‘three-parent baby’ headlines can make the procedure sound quite alarming, almost like Frankenstein science.
Mitochondria are like little batteries inside every cell of the body. They provide cells with the energy that allows them to operate. As well as the DNA in the cell nucleus that is inherited from both your parents and determines all your characteristics, mitochondria also contain a tiny amount of their own DNA. This makes up just 0.1% of total DNA and doesn’t determine anything about who you are like hair colour or height; it only controls the cell’s energy supply.
Also, unlike DNA in the nucleus, mitochondrial DNA comes from your mother only. This is because when you were first made, all the mitochondria came from inside your mother’s egg and none were from the sperm. Severe mitochondrial disease affects about 1 in every 6500 children. Symptoms depend on which part of the body is affected and can include fits, diabetes, blindness, muscle wasting, heart disease, deafness and dementia. Currently, there is no cure and most children diagnosed with a mitochondrial disease die prematurely. Mitochondrial genetics are complex.
When a mutation occurs, only some of the many mitochondria in each cell will carry the mutation. A woman might have so few faulty mitochondria that she herself has few or no symptoms, but her eggs will carry various amounts of healthy and faulty mitochondria.
Whether or not a child develops a disease is down to the biological lottery of which egg is fertilised. Depending on the ratio of mutant to normal mitochondria in the egg, a mother may give birth to one child with a very severe disease and a second child with no disease symptoms at all. This presents a huge dilemma to parents who already have one child affected by mitochondrial disease, of whether to take the chance on having another.
Two techniques exist to replace faulty mitochondria. The first, called Maternal Spindle Transfer (MST), removes the nucleus from one of the mother’s eggs and transfers it into a donor egg with healthy mitochondria that has had its own nucleus removed.
This egg is then fertilised with the father’s sperm and the embryo is implanted into the woman like any other IVF embryo. The second, called pronuclear transfer (PNT), eggs from both the mother and a healthy donor and fertilises them with the father’s sperm. The DNA from the donor’s egg is then discarded, and replaced with the DNA from the mother’s egg. The resulting embryo is ready to grow and is implanted into the mother’s womb.
Both these techniques are controversial for reasons of safety as well as ethics. Years of scientific research has concluded there is no evidence the procedure is unsafe. However, as the procedure leads to a permanent change in the germ line, any unexpected problems could affect people who are not yet born.
Most experts are in favour, however a few have raised concerns about it being a risky uncharted territory that could lead to disability and increased rates of cancer. The Church of England says it is not opposed in principle, but wants to see more scientific research and debate on the ethics and safety before the procedure is legalised.
Some critics argue that this may be the start of a slippery slope, eventually leading to parents selecting genes based on desirable traits to create ‘designer babies’.
However, the health minister and other ethicists have dismissed these claims, saying “there is a big difference between replacing defective mitochondria, and making sure all babies are blue eyed and blonde.” Advocates go on to say that such concerns about a slippery slope should not dissuade us from grasping the vital benefits of medical breakthroughs.
In conclusion, this new technique seems to present the usual trade-offs between benefits to people now and unknowns concerning future dangers. The introduction of all new technologies involves uncertainty about long-term and unforeseen events.
What is clear is that this technique will prevent some of the cruellest and most devastating diseases. We can only hope that in the long-term, the suffering it prevents outweighs any suffering it may create.