Looking at fMRI brain scans and DNA samples from 21,151 people, researchers reveal that a single gene has an impact on intelligence.
The effect is small – a bit more than 1 point – but it’s the biggest effect of a single gene on IQ known so far. New Scientist reports.
It’s not surprising that genetics would account for a large amount of variation in our intelligence, but experts typically find that hundreds of genes contribute, with no one taking all the credit.
An international collaboration of 207 researchers, the Enhancing Neuro Imaging Genetics through Meta-Analysis (ENIGMA) Consortium, was able to tease out a single gene: HMGA2, previously linked with height.
Its effect is small but measurable: it alters IQ by 1.29 points. When people inherit the variant from both parents, they enjoy double the effect: a rise in IQ of about 2.6.
At the site of the relevant mutation, the IQ difference depends on a change of a single DNA letter: from C to T, with C being the “good one,” says study researcher Paul Thompson of the University of California, Los Angeles.
C, or cytosine, raises IQ and even increases the overall volume of the brain… by 0.58% of average brain size. "It's a loss or gain of about 2 teaspoons," Thompson explains.
The research also revealed that a variant of a gene called TESC affects the size of the hippocampus, a memory part of our brain. The gene alters hippocampal size by 1.2% above or below the average.
In adulthood, the hippocampus shrinks by about 0.5% per year, so having that particular gene variant can equate to more than 2 years of aging. Having 2 copies of it is equivalent to 5 years of aging.
Other contributors, such as a good education, exercise, and other environmental factors, could outweigh the effect of single gene variants. But these 2 variants could help improve diagnosis and eventually treatment of brain disorders.
The findings were published in Nature Genetics this week.
Image of fMRI via Flickr