'Designer babies' created via IVF and selected on the basis of genetic combinations for intelligence or height are unlikely to become reality, according to a recent study.

Despite advances in understanding the combined effects of multiple genes on complex traits in humans, researchers at the Hebrew University of Jerusalem in Israel showed that selecting embryos based on their genetic predisposition for height or IQ resulted in an increase of only 2.5 centimetres in height or 2.5 IQ points above average for a sample of five embryos.

In the study published in Cell, the researchers used data from genetic studies to simulate the effects on IQ and height in the offspring of various pairings of couples. They used polygenic scores, which are calculated using genetic data on many of an individual's genes to predict their chances of inheriting a certain trait and combined these with preimplantation genetic testing to maximise the polygenic score for the target traits in their offspring.

When doctors had ten embryos to choose from for a single couple, the selection could result in a gain of three IQ points or 3cm compared with the average for the sample. In a more realistic IVF scenario where a couple has five embryos these figures are even lower.

'For most people this is not a lot,' study co-author Dr Shai Carmi told Inverse. 'I wanted to do these simulations to get a basic idea about what are the expected outcomes of selection.'

The researchers showed that their scores had a limited predictive capacity. From the 28 families studied, in only seven was the tallest child the one predicted by the polygenic score, and in five families the child predicted to be tallest was, in fact, shorter than the average for that family.

The study suggests that there are factors involved in the inheritance of complex traits other than genes. Dr Susanne Haga at Duke University School of Medicine in Durham, North Carolina said in an interview with Science News that factors like diet and exercise need to be considered.

'We still have a way to go to understand the genetic mechanisms behind these traits, and the fact that the environment plays such a critical role cannot be discounted,' Dr Haga said.

Dr Carmi is more optimistic: 'In 20 years or so, when we know much more about genetic variants, it might be possible to achieve bigger gains, particularly for IQ.'

Legislation in the UK currently allows embryo screening only to prevent children from inheriting serious diseases. Some other countries lack specific regulations or guidelines.

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Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.