Scientists and many people affected by mitochondrial DNA diseases have been campaigning for legalisation of mitochondrial replacement therapy (MRT) in Canada, reports CBC. It is already legal in several other countries, including the UK, but MRT is currently controversial due to ethical considerations and a lack of knowledge about its long-term effects.
Mitochondrial DNA diseases are caused by changes to mitochondrial DNA. Since mitochondrial DNA is present in all body cells, the symptoms can present in many different areas of the body, and people are affected in different ways. Patients can experience blindness, hearing loss, diabetes, and a wide range of other symptoms. The disease also first appears at different ages; some people develop it in infancy, while in others the disease isn’t detected until age 70 or even older.
Since mitochondrial DNA is only passed down from the mother, MRT treatments replace the damaged mitochondrial DNA of the mother with healthy mitochondrial DNA from a donor, either before or after fertilisation depending on the technique used. MRT has been successfully performed in several animal studies using mice and Chinese rhesus monkeys, but has only been carried out once in humans. A mother with a severe form of mitochondrial disease, called Leigh’s disease, which often causes premature death, underwent MRT in Mexico. The child was reportedly healthy when born, but the parents declined medical follow-ups so the long-term effects remain unclear.
MRT is already legal in some countries, including the UK, where two women are currently on track to receive the treatment, but remains illegal in Canada under the Assisted Human Reproduction Act. However, many scientists and advocacy groups are campaigning for legal change. One woman who supports this change is Naomi Laliberte, who is affected by a form of mitochondrial DNA disease called mitochondrial complex III deficiency. The condition has caused her neurological, muscular, and digestive issues, and both her children have inherited her disease. Hoping to help her daughter one day have a healthy child who is genetically related to her, Naomi has begun saving monthly to create a fund to pay for MRT treatment if it is legalised.
However, others have ethical concerns about the treatment. Some argue that the risks associated with treating early cells are too great. MRT could disturb natural cell division creating unintended defects in the embryo, and if damaged mitochondria were carried over then the disease would be delayed instead of removed. There are also concerns about which women would be eligible for the treatment, with some, such as Dr Mark Tarnopolsky from McMaster University in Ontario, suggesting that the women worst affected by mitochondrial DNA disease should be the first to receive treatment, but that those with milder disorders might not be entitled to MRT. Despite these concerns, retaining the ban on MRT in Canada while it is lifted in other countries is problematic. Canadian couples seeking MRT may travel abroad for ‘medical tourism,’ and there are fears that Canadian women would undergo the procedure in overseas hospitals with lower medical standards, creating a risk for the women involved and the embryo.
In comparison, other countries where the procedure is legal are already exploring further uses of the technique. In the UK it has been suggested that MRT could be used by lesbian couples who do not have mitochondrial DNA disease, but who want both partners to have a genetic link to the child. In this case, one mother would provide the much larger amount of nuclear DNA, and the other mother the mitochondrial DNA, while a sperm donor would fertilise the egg. However, this remains controversial.