A single gene can affect IQ

A massive genetics study relying on MRI brain scans and DNA samples from over 20,000 people has revealed what is claimed as the biggest effect yet of a single gene on intelligence – although the effect is small.

There is little dispute that genetics accounts for a large amount of the variation in people’s intelligence, but studies have consistently failed to find any single genes that have a substantial impact. Instead, researchers typically find that hundreds of genes contribute.

Following a brain study on an unprecedented scale, an international collaboration has now managed to tease out a single gene that does have a measurable effect on intelligence. But the effect – although measurable – is small: the gene alters IQ by just 1.29 points. According to some researchers, that essentially proves that intelligence relies on the action of a multitude of genes after all.

The variant is in a gene called HMGA2, which has previously been linked with people’s height. At the site of the relevant mutation, the IQ difference depends on a change of a single DNA “letter” from C, standing for cytosine, to T, standing for thymine.

C is the good one. As well as raising IQ by 1.29, it increases the overall volume of the brain – but only by 0.58 per cent of average brain size, adding around 9 cubic centimetres of tissue. It’s a loss or gain of about 2 teaspoons. Learn more here.

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