How can IVF help in the nature-nurture debate?

researchers have found a clever way in which to disentangle the effects of a mother’s behaviour on her developing baby from the effects of her genetics. In other words, scientists have found a way to separate nature from nurture. They can do this by comparing children who were conceived by egg donation via IVF against those conceived also by IVF but using their own mother’s eggs. Here’s Anita Thapar.

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Anita Thapar: The reason we were interested in using a completely novel type of approach is to answer a specific question that many researchers have been interested in for some time. And that’s relating to the effects of what happens to people in the womb, pre-natal risk factors and the effect on health later on. And one of the areas of interest has been exposure to cigarette smoke in the womb and whether that has an effect on health.

It’s known that being exposed to cigarette smoke has an adverse impact on the baby, for example it’s known to lower birth weight. But more recently there’s been a lot of interest in whether it has an impact on children’s behaviour as well.

Chris Smith: So why do you need to study IVF children in order to answer that question?

Anita Thapar: Okay, the interesting thing about looking at the IVF children is because although the majority of children born by IVF are genetically related to the mother who undergoes the pregnancy, there are a group of children who are born by more unusual methods, for example egg donation or by embryo donation, where they may be genetically unrelated to the woman who undergoes the pregnancy.

Chris Smith: So what this means is that you’ve got quite an elegant situation here where you have a baby which is ungenetically related to the mother, so you can look at the situation the mother’s putting the baby in and see if the same factors that would affect, say, a baby born to a mother who smokes who is related to that mother also affect a baby that’s genetically unrelated to that mother.

Anita Thapar: That’s right, and that’s really important because if cigarette smoke has a really true effect on the baby’s health then it won’t matter whether the mother and baby are related, and that’s actually what we found for the effects of smoking on birth weight, didn’t matter whether the mother was related or unrelated, the link remained strong.

However, for antisocial behaviour – by this I’m not talking about very severe behavioural problems but more within the normal range, behaviours such as temper tantrums or fighting – but from antisocial behaviour we found that that wasn’t the case, it was quite different from birth weight. There was a strong link in those genetically related mothers and children but not in the unrelated group, and that suggests that the previously observed links may just be artefactual and just explained by something to do with the mother’s inherited characteristics that she’s passing onto the child, and not a toxic effect of cigarette smoke on behaviour.

Chris Smith: Now I know that you’ve controlled your study by comparing two groups of IVF babies, those related to the mother and those that are genetically not related to the mother, but is there not the possibility that because they’re having IVF they’re already a bit exceptional and that that difference, because there’s clearly already a problem, that could exaggerate any differences that you’re measuring, perhaps sensitivity to cigarette smoke, and therefore the real situation in the normal pregnancy wouldn’t maybe be quite so acute?

Anita Thapar: Well it’s really interesting because, you know, this is a very special and selected group, well how might that affect findings? Well the thing here, we’re not looking at absolute levels of smoking or absolute levels of behaviour. What we’re looking at is the strength of the links between the two. Actually for the genetically related mothers and babies, the strength of the links for both birth weight and behaviour is pretty similar to those found in other studies. And of course the other observational studies, the mothers and children will always be genetically related. So it suggests that the findings might be generalisable.

Chris Smith: It is a very elegant approach that you’ve taken and you’ve used it to just look at one aspect here, which is the effect of smoking on two outcomes. Could you use the same trick, the same technique, to look at other things and, if so, what do you think would be worth looking at?

Anita Thapar: Yes, definitely. We set out to examine a number of different risk factors and a number of different outcomes, so we will be looking at this in the future. We are mainly focusing on risk factors and outcomes that have been previously demonstrated in other types of research, and so where there’s been a question, oh is this really causal or is it, you know, due to some sort of unmeasured inherited factor. The other thing we can look at is prematurity, and again there’s a number of health outcomes that we might be able to look at.

Chris Smith: Anita Thapar from the University of Cardiff discussing a new way to separate environmental factors from genetics. She’s published that work in this week’s edition of the journal PNAS.

Extracted from a February 2009 episode of Breaking Science, originally broadcast on BBC Radio Five Live. Listen to the full episode online.