For the first time, scientists have identified a gene linking the thickness of the grey matter in the brain to intelligence.
Researchers at King's College London and colleagues looked at the cerebral cortex, the outermost layer of the human brain. It is known as 'grey matter' and plays a key role in memory, attention, perceptual awareness, thought, language and consciousness.
Previous studies have shown that the thickness of the cerebral cortex, or 'cortical thickness', closely correlates with intellectual ability, however no genes had been identified.
An international team of scientists, led by King's, analysed DNA samples and MRI scans from 1,583 healthy 14 year old teenagers.
The teenagers also underwent a series of tests to determine their verbal and non-verbal intelligence.
"We wanted to find out how structural differences in the brain relate to differences in intellectual ability. The genetic variation we identified is linked to synaptic plasticity - how neurons communicate," said Dr Sylvane Desrivieres, from King's College London's Institute of Psychiatry and lead author of the study.
"This may help us understand what happens at a neuronal level in certain forms of intellectual impairments, where the ability of the neurons to communicate effectively is somehow compromised," Desrivieres said.
"It's important to point out that intelligence is influenced by many genetic and environmental factors. The gene we identified only explains a tiny proportion of the differences in intellectual ability, so it's by no means a 'gene for intelligence'," she added.
The researchers looked at over 54,000 genetic variants possibly involved in brain development.
They found that, on average, teens carrying a particular gene variant had a thinner cortex in the left cerebral hemisphere, particularly in the frontal and temporal lobes, and performed less well on tests for intellectual ability.
The genetic variation affects the expression of the NPTN gene, which encodes a protein acting at neuronal synapses and therefore affects how brain cells communicate.
To confirm their findings, the researchers studied the NPTN gene in mouse and human brain cells.
They found that the NPTN gene had a different activity in the left and right hemispheres of the brain, which may cause the left hemisphere to be more sensitive to the effects of NPTN mutations.
Their findings suggest that some differences in intellectual abilities can result from the decreased function of the NPTN gene in particular regions of the left brain hemisphere.
The study is published in the journal Molecular Psychiatry.
