Friday June 28 2013
Most genes would come from the parents with 1% from a donor
The Department of Health has published draft regulations on so-called "three-parent IVF".
If the regulations are approved by Parliament, it would make the UK the first country in the world to provide patients with the option of mitochondria replacement techniques. These are innovative IVF-based techniques designed to prevent serious mitochondrial diseases (see below).
Chief Medical Officer Professor Dame Sally Davies said “Mitochondrial disease, including heart disease, liver disease, loss of muscle co-ordination and other serious conditions like muscular dystrophy, can have a devastating impact on the people who inherit it. People who have it live with debilitating illness, and women who are affected face passing it on to their children. Scientists have developed groundbreaking new procedures that could stop these diseases being passed on, bringing hope to many families seeking to prevent their future children inheriting them. It’s only right that we look to introduce this lifesaving treatment as soon as we can.”
The decision follows extensive public consultation carried out by the Human Fertilisation & Embryology Authority (HFEA) in 2012. The public consultation exercise indicated that, overall, there was general support for mitochondria replacement to take place, subject to strict safeguards and careful regulation.
What are mitochondrial diseases?
Almost all of the genetic material in our bodies is contained in 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 cell’s 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 mutations in the genes in the mitochondria. Women carrying these mutations will pass them directly to their child, with no influence from the father.
The HFEA reports that around 1 in 200 children are born each year with some form of mitochondrial disease. Some of these children will have mild or no symptoms, but others can be severely affected by a wide range of distressing symptoms such as seizures, dementia, migraines, heart failure, diabetes and hearing loss. Many children with mitochondrial diseases have a reduced life expectancy.
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. This would mean that the child would have the genetic material of three people – the majority still from the mother and father, but with around 1% of mitochondrial DNA coming from a donor.
What is mitochondria replacement?
There are two IVF mitochondria replacement techniques, called pronuclear transfer and spindle transfer.
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 that 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.
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? (the current thinking is the donor has the right to remain anonymous).
- 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.
What happens next?
Draft regulations are in the process of being produced and are expected to be voted on in Parliament in 2014.
If approved by MPs then it is likely that a number of specialist centres would apply for a licence to offer the treatment to patients.
Any child born using this techniques will be assessed carefully for the rest of their life to see if the techniques are safe and do not lead to long-term complications.
Edited by NHS Choices. Follow Behind the Headlines on twitter.