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Mind

The Coming Age of Fetal Genomics

Neuroskeptic iconNeuroskepticBy NeuroskepticJuly 11, 2012 4:57 AM

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It's 2020. A young woman and her partner have just found out that she's pregnant with her first child. and they're going to be parents.

They're overjoyed, of course. But they're also worried. They've seen the adverts warning parents-to-be about the risk of de novo mutations - genetic mistakes that occur inside sperm or egg cells, and affect the child. These mutations, the ads say, are much more common than previously believed and they can cause all kinds of problems: intellectual disabilities, autism, infertility, mental illness, heart malformations - pretty much anything.

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The scariest part? Because these are new mutations, out of the blue, they can affect any family. A clear family history is no protection. They don't discriminate by race or lifestyle. It's just the luck of the draw - except that older parents are at much higher risk, especially older fathers. In the case of our couple, she's 28 and he's 32. Perfectly normal for this day and age - but very old in biological terms. Humans evolved to be grandparents by 32, not parents. "The stakes couldn't be higher. Why leave it to chance?"

So they don't. Instead, they buy a $100 test kit, they each provide a small blood sample and send it off to one of the companies offering fetal genome testing. At the testing lab, they can separate out the mother's DNA from that of the fetus, both of which are present in the mother's blood. By comparing the fetal genome to the mother's and father's, it's easy to spot de novo mutations. If a certain gene doesn't match either the mother or the father's sequence, it's mutated.

A few days later the results are back. There are several mismatches detected. Most are benign - they're not predicted to have any biological effects. But there's one, a deletion of a few thousand bases in a gene involved in brain development. This deletion is predicted to raise the risk of epilepsy and autism from 1% to 10% apiece.

The parents now have a decision to make. The mutation is a one off, it's not inherited. If they conceive again... roll the dice again... and it'll be gone. Do they terminate?

Like the adverts say, "Some people disagree with this, but we say there's only one person who really matters: your baby."

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This is likely to become possible in the next few years.

A paper just published in Nature reports on the Non-invasive prenatal measurement of the fetal genome. The technique relies on the fact that the blood of a pregnant woman contains DNA: hers, obviously, but also that of the unborn child. This cell-free DNA can be extracted and genotyped.

This has been possible for a few years, but until now, only fairly crude genetic information could be detected. An extra chromosome, such as in Down syndrome, is pretty easy to spot. This technique is already used to diagnose Down's syndrome and a few other disorders prenatally.

But those diseases are just the low-hanging fruit at the tip of the iceberg, if you see what I mean. To gather the kind of detailed genomic information that could diagnose thousands of disorders is harder: the fetal and maternal genomes are mixed up, and the challenge is to tease them apart. But according to the Stanford geneticists behind the Nature paper, and other teams, it's now possible as early as the first trimester.

What makes the new method so revolutionary is that it is, as the title of the paper says, non-invasive. It's already possible to sequence a fetal genome, but it takes a surgical procedure involving inserting a needle into the womb, and a degree of risk. It's not something you can just sit down and do - but blood samples are. So cell-free DNA will make fetal genomics a personal choice, a commercial product.

The resolution's still not 100%, but inevitably, it will become cheaper, faster and more accurate as technology advances. This year we're expected to see the cost of reading a whole human genome falling below $1000. Fetal genomes will be more expensive, but not enormously so. In 5 or 10 years, it's likely to be affordable.

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What will happen? I think there'll be demand for such services. Most parents won't do it, but enough people will that it will be a major issue. Just look at countries where boys are more valued than girls: a lot of sex-selective abortion happens. Today, it's limited to gender, because it's easier to determine a fetus's sex than its genome. In 5 or 10 years, they'll both be easy.

With demand will come companies to supply these services and, inevitably, advertizing. I doubt these adverts will be on TV, because there will be opposition to the whole idea and boycotts of broadcasters who run them. But we'll be getting spam emails about it. People will worry even over the harmless mutations: a variant won't need to be really associated with a disease, just believed to be, to make people panic.

Socially, it's likely to be divisive. The anti-abortion types will obviously not approve. But it will drive a wedge between those who support abortion but oppose "discriminatory" abortion against the disabled, and those who support the right to terminations 'for any reason, or none'.

Politically, there will be pressure to regulate this, but legally, it'll be tricky. I can't see how you'd prove that any given abortion is motivated by genetic concerns, so unless you ban abortion outright, that won't work. Banning fetal (or all) genomics except under medical supervision might be possible, but people could always go (or send a few drops of blood) abroad to get around that.

I'm not sure where I'll stand on this, but it looks very likely that we'll each have to make a decision in the coming years.

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Fan HC, Gu W, Wang J, Blumenfeld YJ, El-Sayed YY, and Quake SR (2012). Non-invasive prenatal measurement of the fetal genome. Nature PMID: 22763444

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