Saturday, September 10, 2005

Three parents?

I've been annoyed with the press coverage of the recent decision by the UK's Human Fertilisation and Embryology Authority (HFEA) to allow scientists to research a technique that treats inherited mitochondrial disorders.

For those who don't know, mitochondria are the organelles that power the cell by burning glucose with oxygen to release energy. They are separate from the nucleus (which contains the vast majority of DNA) and have their own DNA, which codes for various proteins used only in the mitochondria. They're inherited from the mother because the sperm cell's mitochondria are excluded from the fertilized egg.

Sometimes these mitochondria will have defects in their DNA. If that's the case, usually in a fertilized egg you'll have some normal and some defective mitochondria. As the fertilized egg divides and divides again, the mitochondria divide independently and the normal and defective mitochondria end up randomly distributed throughout the embryo. Depending on which organs the defective mitochondria end up in, the mitochondrial disease causes a variety of problems (the problems are more severe if the defective mitochondria are in energy-intensive tissues like muscle, brain, or liver). So it's possible that if you're a woman with a fairly mild mitochondrial disease, your child could have a much more severe form.

The proposed treatment works as follows: a woman with mitochondrial disease and her partner use in vitro fertilization to make a fertilized egg, as normal, but then the nuclei (which contain the vast majority of DNA) are taken out and put into a healthy donor egg whose nucleus has been removed. The resulting zygote has genetic material from two parents plus a contribution of mitochondria from a third person.

Doesn't sound so bad, does it? But everywhere I look on the newsstand, it gets the sensationalistic headline of "Embryos with three parents" and "Embryo with two mothers" and so on, even though the third person contributes only 13-14 protein-coding genes (the rest of the mitochondrial genes are for ribosomal RNA and transfer RNA, which allow the mitochondria's own protein synthesis machinery to function independently of the cell's protein synthesis), compared to the estimated 20,000-25,000 genes that each parent contributes. The headline "three parents" is, I think, deeply misleading because it suggests that the three parents make similar genetic contributions to the child, along the lines of the aliens in the middle section of Asimov's The Gods Themselves.

In fact, I don't see that this is so different from surrogate pregnancy, where a fertilized egg is implanted in another woman's uterus - the womb has a huge influence on the growing embryo, so this "two mothers" idea applies just as much, if not more, to surrogate pregnancy as to this potential (emphasis on potential) treatment for mitochondrial disease. The disproportionate focus on mitochondrial donation seems to me to reflect an unhealthy fixation on genetic determinism and the continuing perception of nature and nurture as opposites.

But the top prize in misleading headlines must go to The Daily Telegraph, with the breathless headline, "Designer babies to wipe out diseases approved" - as if mitochondrial diseases were an infection that can be "wiped out." "Wiped out" also carries the connotation of eugenics, as if these babies were part of a plot to liquidate anyone with a mitochondrial disorder, or to prevent people with mitochondrial disorders from reproducing. Lest one think this was just a fault on the headline writer's part, the term "wipe out" is also used twice in the text.

We have enough trouble having a rational debate about reproductive technologies without misleading press coverage. Let's try to keep the public informed, not misled by scary headlines darkly hinting at eugenics.

PS: Via Flags and Lollipops, a column lambasting UK media's coverage of science in general with the following dead-on quote:
It is my hypothesis that in their choice of stories, and the way they cover them, the media create a parody of science, for their own means. They then attack this parody as if they were critiquing science.
Read the rest for a simultaneously entertaining yet thoroughly depressing analysis of how the press misrepresents science. The irony is that they then wonder why public mistrust of science has increased so much in recent years.

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