The UK parliament is today voting on whether mitochondrial replacement techniques – involving three-parent babies – can be used in women who carry mitochondrial disease. If given the go-ahead, the procedure would avoid children being born with serious diseases due to mutations in mitochondrial DNA
What are mitochondria?
Mitochondria are the energy generators of our cells. They have their own DNA which is passed down by the mother and is distinct from the chromosomes in the nucleus. Mutations in the mitochondrial DNA can lead to blindness, seizures, dementia or mental impairment, and early death. There is currently no cure.
What options are there for women at risk of passing on mutated mitochondrial DNA?
They can avoid having children, or any further children if the first was affected. They can hope that their child will be OK, which is very risky. They can adopt or use egg donation, in which case the child will not be genetically related to them. Or they can use pre-implantation genetic diagnosis to look for embryos with a sufficiently low proportion of mutant mitochondrial DNA.
This, however, is not possible where there is a high proportion of abnormal mitochondrial DNA or where it is all abnormal, which is common. Mitochondrial replacement offers another option for these women.
What do the techniques involve?
It is a form of IVF that involves transferring the nucleus from the prospective mother's egg into a donor egg with healthy mitochondria, either before or after it is fertilised by the woman's partner. The resulting child will have nuclear DNA from the woman and her partner, and mitochondrial DNA from the donor.
The procedures have been successfully trialled in monkeys and if the techniques are approved for use in the UK, the regulations will be in place for clinical trials in people – a world first.
How many women could it help?
A recent study carried out by the researchers at Newcastle University pioneering the techniques estimated that 2473 women in the UK, and 12,423 women in the US, aged between 15 and 44 years, are at risk of passing on potentially lethal mitochondrial DNA to their children. This equates to an average of 152 births per year in the UK, and 778 births per year in the US.
But because the change to the mitochondrial DNA is permanent, the technique will not only prevent the child inheriting mitochondrial disease but also any of their descendants.
Why is the procedure so controversial?
For a number of reasons. First, there's the fact that the child will inherit DNA from three people. For many, this isn't an issue because the donor's mitochondria contribute just 37 genes to the child, compared with more than 20,000 from the parents. That's a negligible amount, and far less than you would gain from a blood transfusion or organ transplant.
We know that mitochondria do more than simply power our cells, but in a recent New Scientist piece, Robin Lovell-Badge from the MRC National Institute for Medical Research in London explained why none of these "extra" functions are relevant to mitochondrial replacement.
Then there are concerns that changes to the mitochondrial DNA might affect future generations in unknown ways. Again, most researchers think that the unintended consequences are likely to be minimal.
Are we ready to allow mitochondrial replacement?
This is what the Members of Parliament will be debating today. For the past four years, an independent panel convened by the UK Human Fertilisation and Embryology Authority (HFEA) has been providing advice to the government. During this time, there has been several round-ups of the science as well as ethics reports and a public consultation.
In June last year, the panel said the work done so far suggested that the technique is safe enough to try in clinical trials as long as several extra experiments are carried out first and children born as a result of the technique are followed up for an extensive period. The extra assessments could be done in the next 18 months to two years after the regulation has passed.
See a timeline of the debate
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