The Science Behind Mitochondrial Donation

The two mitochondrial donation techniques being developed are maternal spindle transfer and pronuclear transfer. They involve transferring nuclear genetic material from the affected mother’s egg into a donor egg that has had its nuclear DNA removed and retains only its healthy mitochondrial DNA; the resulting child therefore does not inherit the mitochondrial disease.

 

Image showing how the nuclear DNA from an egg with unhealthy mitochondria is transplanted into an egg with healthy mitochondria that has had its nuclear DNA removed

Image of mitochondria in a body cellThree People’s DNA?

Children who have undergone mitochondrial donation will have DNA from three people. However, it is important to note that when the new mitochondrial DNA molecule is introduced, it is only replacing 37 mtDNA genes (contributing about 0.1 per cent of a person’s genetic make-up), compared with approximately 22,000 genes in the nucleus, which are not replaced. The mtDNA contribution is important for converting food into energy but appears to make no significant contribution to appearance, behaviour or other features, which are determined by the nuclear genes and environment.

Some groups have made sensationalist claims about the techniques being inappropriate because the children could be said to have three parents. However, this is “misleading, inappropriate and unhelpful” according to the Nuffield Council on Bioethics in London, which in 2012 reviewed the procedures from an ethical standpoint.

Mitochondrial replacement can be compared to changing the sparkplugs in an engine or a transplant into a patient with organ failure.


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