The research suggests that teenagers with a particular genetic variant have a thinner cerebral cortex, commonly known as grey matter, in the left hemisphere of the brain. Teenagers with this genetic variant were found to do less well in verbal and non-verbal reasoning tests. This is the first time a genetic connection between intelligence and grey matter has been identified.
Grey matter is the outermost layer of the human brain, and plays a key role in memory, attention, perceptual awareness, thought, language and consciousness. The thickness of the grey matter is closely related to a person's intellectual ability.
Dr Sylvane Desrivières, lead author, from King's College London's Institute of Psychiatry, said: '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'.
'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'.
Researchers analysed DNA samples and brain scans from 1,583 healthy 14-year-olds, who were also given a series of tests to determine their verbal and non-verbal intelligence.
The researchers looked at more than 54,000 genetic variants possibly involved in brain development, and found that the genetic variant affects the expression of the NPTN gene. This gene encodes a protein affecting how brain cells communicate.
The NPTN gene was found to have different activity in the left and right hemispheres of the brain. The left hemisphere may be more sensitive to the effects of NPTN mutations, and differences in intellectual ability could be caused by the decreased function of the NPTN gene in parts of the left hemisphere.
But Dr Desrivières cautioned: '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"'.
Researchers hope that this finding will help explain the biological basis of psychiatric disorders involving impaired cognitive ability such as schizophrenia and autism.