'Three-parent babies' a step forward

'Three-parent babies' a step forward

IT HAS been possible for some time now to make a test-tube baby with three biological parents.

The United States banned this in 2001, and Australia followed suit in 2002.

But Britain's Parliament recently voted in favour of just such technology.

The idea is to use it to deal with a rare problem that can occur in a mother's eggs.

Mitochondria are minuscule organs found in every cell in our bodies, and they are precisely functioning micro-machines that generate energy from food to power all life processes.

Without energy, no life can exist. Thus no life can exist without mitochondria.

The three-parent technique can help where a mother's eggs have poorly functioning mitochondria, and require a second woman to donate a healthy egg.

First, the nucleus of the donor's egg is removed and discarded.

Next, the nucleus of the mother's egg is extricated and inserted into the donor egg, replacing the original.

The hybrid egg is then fertilised with the father's sperm, to produce a viable embryo.

The nucleus of the cells of this early embryo contains DNA from both the father and mother.

But the second woman contributes no DNA to the nucleus of the embryo's cells, because the nucleus with her DNA was removed and discarded in Step One of the process.

All that remained of the donor's egg was its cytoplasm, the jelly-like soup that holds a cell's contents together.

Cytoplasm always sits around and outside the nucleus.

It nourishes the nucleus but, crucially, it is also where all of a cell's mitochondria are located.

So transferring the nucleus from the mother's egg into the second woman's egg after its own nucleus is removed means that the donor's cytoplasm with its healthy mitochondria will power the nucleus of the mother's egg.

Without this "three-parent" procedure, children conceived by the mother might inherit her mitochondrial disorder and they may develop muscular dystrophy, epilepsy, stroke and mental retardation.

About one in every 6,500 babies is affected, facing drastically shortened lifespans.

Just as heartbreaking is that women with mitochondrial disorders find it very hard to have children at all.

While the nucleus of their eggs can be fertilised, the resulting embryo may not survive because their mitochondria are defective.

The "three-parent" procedure offers new cytoplasm with healthy mitochondria to let the embryo thrive.

Why then do some oppose the procedure?

While most of a cell's DNA is found in the nucleus, a tiny bit is also found in mitochondria, which are always outside the nucleus.

Uniquely, this mitochondria DNA is derived only from the mother but not the father.

But it contains only 37 genes, compared to the 20,000 genes in the DNA of the nucleus we all get from both our parents.

It is those 20,000 genes that determine our physical and, perhaps, mental traits, not the 37 mitochondrial genes.

Since no genes in the nucleus are altered in the "three-parent" technique, the baby's physical and mental traits remain those it inherits from its father and mother, not the second woman.

So the procedure presents no slippery slope to making designer babies, as some fear.

If the resulting offspring is healthy and female, she could theoretically have healthy offspring eventually, thus transmitting the the second woman's mitochondria DNA to future generations as well.

This means that this technique can help prevent mitochondrial disorders, which is a good thing.

Yet, some oppose it. In Britain, the Catholic Church objects because it "involves the destruction of human embryos".

The method described above involves the manipulation of eggs from the mother and donor before they are ever fertilised - and therefore before an embryo is created - so no embryonic life is lost.

Only the donor egg's nucleus is discarded. Besides, a woman loses unfertilised eggs in her monthly periods.

In a variation, however, the mother's egg is fertilised in a petri dish with the father's sperm.

The resulting embryo's nucleus is then removed and transferred into a donor egg emptied of its own nucleus.

This reconstituted embryo has both the father and mother's DNA combined in the nucleus.

Outside that nucleus, in the cytoplasm, is the donor egg's healthy mitochondria DNA.

So the original embryo lives on in its reconstituted form with new mitochondria.

If the reconstituted embryo proves non-viable, some embryonic life is lost.

But that is like an early miscarriage.

The Anglican Church accepts embryo research "to alleviate human suffering" but wants more studies to establish the procedure's safety and also prove that the child will not inherit characteristics from the donor's mitochondria DNA.

Many scientists feel that the available research is enough to allay these worries, so the Anglican objection comes down to how much research it deems sufficient.

Religious opposition aside, why is the prospect of three-parent offspring so disconcerting that it is banned in, say, the US?

Perhaps three adults possibly having parental rights could potentially lead to protracted child custody battles.

But these won't pose some category of legal problems never encountered before.

Other reproductive technologies have already resulted in three groups of possible "parents" - first, the couple planning to raise the child;second, the sperm and/or egg donor; and, third, a woman surrogate who bears the child, as well as her husband.

So, in theory, a child might well have up to six parents.

If divorce should occur, which adult is to provide child support or gets custody or visitation rights?

In such cases, biology will matter but won't be decisive as most courts will focus on a child's best interests instead.

Overall, this technology, especially the first option in which no embryos are pre-created, seems like a good thing that can help avert some medical tragedies - and give us a few more babies.

andyho@sph.com.sg


This article was first published on Mar 1, 2015.
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