Genetics and stem cells

MPs vote to give the go-ahead to three-parent IVF

“In an historic move, MPs have voted in favour of the creation of babies with DNA from two women and one man,” BBC News reports. The UK is set to become the first country to license the technique known as three-parent IVF, which could potentially be used to prevent babies being born with mitochondrial diseases.

Many researchers welcomed the news.

Doug Turnbull, Professor of Neurology at Newcastle University, said: “I'm delighted for patients with mitochondrial disease. This is an important hurdle in the development of this new IVF technique ... and something the UK should rightly be proud of.”

The news was also welcomed by government officials. Professor Dame Sally Davies, the Department of Health’s Chief Medical Officer, said: “I’m delighted that MPs have voted to approve these regulations and hope the Lords will do the same. Mitochondrial donation will give women who carry severe mitochondrial disease the opportunity to have children without passing on devastating genetic disorders. It will also keep the UK at the forefront of scientific development in this area.”

Though other experts were not so optimistic. Dr Paul Knoepfler, associate professor at the University of California, Davis, is quoted in The Daily Telegraph as saying that the UK could be on the brink of a “historical mistake”. “Since this is uncharted territory and the children born from this technology would have heritable genetic changes, there are also significant unknown risks to future generations.”

The proposed change to the law, specifically an amendment to the Human Fertilisation and Embryology Act, will now go the House of Lords, who do have the power to delay the passage of the amendment into law.

What are mitochondrial diseases?

Almost all of the genetic material in our bodies is inside the cell nucleus that contains 23 chromosomes inherited from our mother and 23 inherited from our father. However, there is also a small amount of genetic material contained in cellular structures called mitochondria, which produce the cells’ energy. Unlike the rest of our DNA, this small amount of genetic material is passed to the child only from the mother. There are a number of rare diseases caused by gene mutations in the mitochondria. Women carrying these mutations will pass them directly to their child, with no influence from the father.

The IVF technique being considered aims to prevent these “mitochondrial diseases” by replacing the mother’s mitochondria with healthy mitochondria from a donor, thereby creating a healthy embryo.

Despite the media-friendly nickname, the techniques do not really constitute three-parent IVF. Only 1% of DNA would come from the “third parent”.

It is probably more accurate to consider the technique as a form of donation, akin to blood donation.

How many women could benefit from the technique?

modelling study published last month estimated that 2,473 women in the UK could benefit from the new IVF technique. This was based on the proportion of women known to be at risk in the north east of England, so does not take into account variations across the UK or US in terms of ethnic diversity or average maternal age.

The researchers based these estimations on data on how many women have a mitochondrial DNA (mtDNA) mutation and whether this affects their fertility.

The researchers concluded if all women in the UK estimated to have an mtDNA mutation wanted to have a child and had the new IVF procedure, this could benefit 150 births per year.

What is mitochondria replacement?

There are two IVF mitochondria replacement techniques currently at the research stage, called pronuclear transfer and spindle transfer. These are the techniques under debate.

Pronuclear transfer involves an egg during the process of fertilisation. In the laboratory, the nucleus of the egg and the nucleus of the sperm, which have not yet fused together (the pronuclei) are taken from the fertilised egg cell containing the “unhealthy” mitochondria and placed into another donor fertilised egg cell, which has had its own pronuclei removed. This early-stage embryo would then be placed into the mother’s body. The new embryo would contain the transplanted chromosomal DNA from both of its parents, but would have “donor” mitochondria from the other egg cell.

The alternative mitochondria replacement technique of spindle transfer involves egg cells prior to fertilisation. The nuclear DNA from an egg cell with “unhealthy” mitochondria is removed and placed into a donor egg cell that contains healthy mitochondria and has had its own nucleus removed. This “healthy” egg cell can then be fertilised.

Pronuclear transfer and spindle transfer are said to be potentially useful for the few couples whose child may have severe or lethal mitochondrial disease, and who would have no other option for having their own genetic child. It is estimated that in the UK, around 10-20 couples a year could benefit from these treatments. 

What ethical concerns have been raised about the techniques?

There are obvious ethical implications from creating an embryo with genetic material from three parents.

Among the questions raised are:

  • Should the details of the donor remain anonymous, or does the child have the right to know who their “third parent” is?
  • What would be the long-term psychological effects on the child knowing it was born using donated genetic tissue?

Opponents of these types of treatments cite what can be broadly summarised as the “slippery slope” argument. This suggests that once a precedent has been set for altering the genetic material of an embryo prior to implantation in the womb, it is impossible to predict how these types of techniques might be used in the future.

Similar concerns were raised, however, when IVF treatments were first used during the 1970s. Today, IVF is generally accepted.  

NHS Attribution