One smart snip: uncovering the genetics of intelligence

Ever wondered how you got your smarts? At least some of it is genetic, with thousands of variations in many parts of your genome contributing to your overall IQ.

However, researchers have now discovered that even a tiny variant in a single gene can have a significant impact on your intelligence.

An international consortium of researchers have found that just one single nucleotide polymorphism (SNP, pronounced “snip”) in the gene HMGA2 is associated with both brain size and general intelligence.

Individuals who had cytosine instead of thymine at the key location had larger brains and scored more highly on standardised IQ tests.

“This is a really exciting discovery: that a single letter change leads to a bigger brain,” said Paul Thompson, Professor of Neurology at the David Geffen School of Medicine at the University of California Los Angeles, and a member of the UCLA Laboratory of Neuro Imaging

“We found fairly unequivocal proof supporting a genetic link to brain function and intelligence. For the first time, we have watertight evidence of how these genes affect the brain. This supplies us with new leads on how to mediate their impact.”

The consortium, called Project ENIGMA (Enhancing Neuro Imaging Genetics through Meta-Analysis), set out to uncover genetic variants that impacted risk of brain disease and mental illness.

The study was conducted over three years and involved over 200 scientists from 100 institutions worldwide, including twin study experts Nick Martin and Margaret Wright from the Queensland Institute for Medical Research in Brisbane, Australia.

They set out to find two things, says Thompson. “We hunted for genes that increase your risk for a single disease that your children can inherit.

“We also looked for factors that cause tissue atrophy and reduce brain size, which is a biological marker for hereditary disorders like schizophrenia, bipolar disorder, depression, Alzheimer's disease and dementia.”

Project ENIGMA researchers measured the size of the brain and its memory centres in thousands of MRI images from 21,151 healthy people while simultaneously screening their DNA.

“Our individual centres couldn’t review enough brain scans to obtain definitive results,” said Thompson.

“By sharing our data with Project ENIGMA, we created a sample large enough to reveal clear patterns in genetic variation and show how these changes physically alter the brain.”

The researchers found that individuals with smaller brains had a consistent changes in their genetic code and also experienced diminished memory centres, lending an insight into how genes affect our brains and can lead to disorders and mental illness and raising the prospect of new treatments.

“Millions of people carry variations in their DNA that help boost or lower their brains’ susceptibility to a vast range of diseases,” said Thompson.

“Once we identify the gene, we can target it with a drug to reduce the risk of disease. People also can take preventive steps through exercise, diet and mental stimulation to erase the effects of a bad gene.”

The discovery of the relationship between the single variation and brain size and intelligence was a serendipitous finding that emerged from the piles of data.

The study was published today in Nature Genetics.