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Birth of hope v unknown terror
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| Andy Ho |
Sat, Feb 09, 2008
The Straits Times
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HOW can a baby have three genetic parents? British scientists recently claimed a first in making 10 human embryos with genes or DNA from one man and two women. This could benefit infertile couples who want offspring with both their DNA - only there would be a small but crucial bit of another woman's DNA.
Under the new technique, the father's sperm is used to fertilise the nucleus of the mother's egg in the test tube. This fertilised nucleus is then removed and inserted into another woman's egg from which the nucleus has been extricated beforehand. What the second woman contributes is her egg's cytoplasm - the jellylike soup that holds a cell's contents together and sits around the nucleus, nourishing it.
Cytoplasm contains, crucially, mitochondria, tiny organs found in every cell in our bodies. They produce energy to power life's processes. Without them, life would not be possible.
The reason for the transplant is that, while the mother's eggs can be fertilised, they cannot survive because they have defective mitochondria. So they cannot develop successfully into embryos, fetuses and babies. What the procedure offers to the fertilised nucleus of the mother's egg is new cytoplasm with healthy mitochondria to provide it with energy to thrive.
| What's the catch? The problem is that all mitochondria also contain their own set of genes that are, uniquely, derived only from the mother but not the father. So when we speak of the human genome as having been fully mapped already, we are really talking about the human genome in the nucleus. It contains the 20,000 genes that we get from both our fathers and mothers, and which determine our physical and, perhaps, mental traits.
Because mitochondria carry their own set of genes, we each have a second genome. Although this mitochondrial genome contains only 37 genes, mistakes in these can lead to serious diseases such as muscular dystrophy, epilepsy, strokes and mental retardation.
No genes are altered in this technique, of course; some bad ones are just swapped for some good ones. But even if 99 per cent of the genetic material in the new embryo comes from the 'real parents', the centrality of the mitochondrial genome to life means the third genetic parent makes a not insignificant contribution. And if the 'triganous' offspring is female, she can theoretically transmit the third parent's mitochondrial genome to future generations.
Still, this new technique is not as giant a step as it may sound. It merely inverts a technique called cytoplasmic transfer, now illegal in the United States and Australia but not the United Kingdom. That procedure is used for women who can conceive but cannot carry through a pregnancy because the fertilised egg will not implant securely in their wombs.
What doctors do is to suck out cytoplasm from healthy donor eggs and inject that into the weaker eggs of such women to boost their mitochondria. Once these turbocharged eggs are fertilised in the test tube with the husband's sperm, the embryo is implanted in the mother's womb. This technique was applied to humans without prior research in primates. Although more than 30 babies have been born using cytoplasmic transfer, little is known about their health.
Because there was no extensive research evaluating its possible risks, the technique was banned in the US in 2001 and in Australia in 2002. A review of the legislation in 2005 in Australia led to a reaffirmation that 'the creation of ...embryos with more than two genetic parents...for reproductive purposes should remain prohibited' - with no exceptions even if it is clinically proven to be safe. Those who break this law can be imprisoned for up to 10 years.
In contrast to cytoplasmic transfer, the newer British technique results in an embryo that starts off life with cytoplasm bearing the mitochondrial genome from the second mother only, compared to the mix of cytoplasm - and thus of mitochondrial genomes - from both mothers in the older procedure.
If anything, the newer technique sounds a little safer. So if the offspring turn out to be healthy - and they in turn have healthy offspring eventually - this could be just another form of therapy available to infertile couples.
Apart from the safety considerations, why have concerned Western governments banned the creation of embryos with more than two genetic parents? This ban contrasts starkly with the lack of oversight of most IVF techniques, including surrogacy and egg donations, where there are two biological but not genetic mothers. These techniques were also pressed into clinical service with amazing haste and no prior studies to establish their safety. So what is it about the New Embryo that is so unsettling?
I think the discomfort reflects the unsettled status of the embryo, something akin to the unsettled status of the foetus in the abortion debate. Newer technologies enable the creation of embryos that are clones of a pre-existing person, or those that are chimeric, where animal and human DNA are commingled, and now ones with two genetic mothers as well.
With foetuses, we were always sure they would turn out to be fully human if they were ever brought to term. The dispute was just over the point at which they became human. The New Embryo, though, could turn out to be human - or part-human, part-animal, or a mutant of some sort.
If such transformations are possible, we may have to ask ourselves what it means to be a human being. We may have to examine the meaning of our membership in human families and communities. Prohibiting the creation of such embryos may well short-circuit such fears - but it will not make them go away. Dealing with the issue head on - as the British will have to - may be the better road to take.
andyho@sph.com.sg
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