embryo

Three-parent embryos need a new name. Both the FDA and the UK government have recently opened up dialogues on the topic of mitochondrial donation to avert diseases caused by mitochondrial genetic defects. These genetic diseases are varied, but can cause blindness, deafness, diabetes, neurological disorders and can prevent women from conceiving altogether. It is estimated that 1 in 200 children in the UK are born with mitochondrial illnesses.

Mothers who suffer from these mitochondrial diseases will pass them on to their children, as mitochondria all come from the mother’s egg cell with none coming from the sperm cell. With the donation of healthy mitochondria from a third party, the children could be born without the risk of suffering from the same conditions. But would these children then count as having three parents?

The size of the mitochondrial genome compared to nuclear genome would disappear in rounding. Mitochondrial DNA is approximately 16,600 base pairs compared to approximately 3,200,000,000 in nuclear DNA, making mitochondrial DNA equal to 0.0005% the size of genomic DNA. If Tolstoy’s War and Peace were a human genome, the mitochondrial DNA would be equivalent to just more than the first four paragraphs.

In this context, it is easy to see how the name ‘three-parent embryos’ is somewhat misleading. Most reports (ironically including this one) have gone with this more emotive title to gather people’s interest, but a more analogous situation which has been used is that of organ donation rather than parenthood. Issues surrounding the technique are real and those likely to be raised include the rights of the mitochondrial donor, the ‘slippery slope to eugenics’ argument and the potential health risks to the mother and children.

The third argument is likely to be the main point of any serious conversation. Two techniques are under discussion: Maternal Spindle Transfer (MST) and Pro-Nuclear Transfer (PNT). MST involves removing the maternal DNA from the diseased egg before fertilisation and implanting it in a healthy egg which has had its nuclear DNA removed. PNT involves removing the DNA from a fertilised egg before the DNA of the egg and the sperm have fused and implanting it in a healthy egg which has had its nuclear DNA removed.

Both techniques are quite far removed from the ideas of critics who have been arguing that people will begin selecting their children for having blue eyes and high intelligence etc. The UK has already drafted legislation (an amendment to the Human Fertilisation & Embryology Act 1990) which will allow for the use of the technique in cases of mitochondrial disease. This amendment specifically states that an acceptable donor egg is one “ whose nuclear or mitochondria DNA has not been altered.” The UK has started an open consultation period on the amendment which will run until the 21stMay.

Meanwhile in the US, their open consultation is a couple of steps behind the Brits. The FDA held a meeting of their Cellular, Tissue and Gene Therapies Advisory Committee on February 25thand 26thto discuss the current state of research in the field, potential risks to mother and child, how human trials could be designed and what controls could be used to minimise risks.

There is a long way to go for this to enter clinics and regardless of the animal models, we will only be able to measure the success of the technique once trials begin in humans. If it does prove a success, thousands of children could be born without terrible genetic illnesses in one of the first true genetic therapies.

embryo

Regulatory Bodies Discussing 'Three-Parent Embryos'

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