British scientists believe they have made a huge step forward in the understanding of the mechanisms of human intelligence. That genetic inheritance must play some part has never been disputed. Despite occasional claims later dismissed, no-one has yet produced a single gene that controls intelligence.

But Michael Johnson of Imperial College London, a consultant neurologist and colleagues report in Nature Neuroscience that they may have discovered a very different answer: two networks of genes, perhaps controlled by some master regulatory system, lie behind the human gift for lateral thinking, mental arithmetic, pub quizzes, strategic planning, cryptic crosswords and the ability to laugh at limericks.

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As usual, such research raises potentially politically-loaded questions about the nature of intelligence. “Intelligence is a composite measure of different cognitive abilities and how they are distributed in a population. It doesn’t measure any one thing. But it is measurable,” Dr Johnson said.

About 40% of the variation in intelligence is explained by inheritance. The other factors are not yet certain. But the scientists raise the distant possibility that armed with the new information they may be able to devise ways to modify human intelligence.

“The idea of ultimately using drugs to affect cognitive performance is not in any way new. We all drink coffee to improve our cognitive performance,” Dr Johnson said. “It’s about understanding the pathways that are related to cognitive ability both in health and disease, especially disease so one day we could help people with learning disabilities fulfil their potential. That is very important.”

The two networks, known just as M1 and M3, one with roughly 1000 genes, the other with more than a 100, also play a role in neurodevelopmental disorders such as epilepsy, schizophrenia and autism. The functions do not seem to overlap, and the role of each network has yet to be settled.

“We know that genetics plays a major role in intelligence but until now haven’t known which genes are relevant. This research highlights some of the genes involved in human intelligence and how they interact with each other,” Dr Johnson said. “What’s exciting about this is that the genes we have found are likely to share a common regulation, which means that potentially we can manipulate a whole set of genes whose activity is linked to human intelligence.”

The discovery is testament to the power of patience, patients and the assembly of huge sets of data. The Imperial College scientists started with evidence from 100 mouse brains, 122 samples of human brain, and 102 whole human brains preserved postmortem. Such indicators of a genetic connection between neurodevelopmental problems or memory and understanding were then checked against records of 6,732 people in the “Generation Scotland” family health study, which tracks the life history of thousands of volunteers, and repeated in 1,003 healthy people who had volunteered to take part in a study called the Lothian Birth Cohort 1936.

It assessed a range of cognitive abilities – among them memory, attention, processing speed and reasoning – and then it combined the results with genetic information donated by healthy people who had taken IQ tests, and from people with autism spectrum disorder and intellectual disability. Included in the research were studies of people who had undergone neurosurgery for epilepsy.

Then the scientists then harnessed massive computing power to see what the data could tell them. They found that the genes that influenced the intelligence and ability of healthy people were the same ones that impaired cognitive ability and caused epilepsy when mutated. If researchers understand what may go wrong in the interplay of inheritance that delivers human reasoning or memory, they might – the possibility for the moment is only theoretical – be able to devise new ways to deliver help.

“Traits such as intelligence are governed by large groups of genes working together - like a football team made up of players in different position,” he said. “We found that some of these genes overlap with those that cause severe childhood onset epilepsy or intellectual disability,”

The researchers may have identified a pool of players in a team: they still have to identify how the players co-operate, which are the key players and precisely what game is being played.

“Eventually we hope that this sort of analysis will provide new insights into better treatments for neurodevelopmental disease such as epilepsy, and ameliorate or treat the cognitive impairments associated with these devastating diseases.”

by Tim Radford For The Guardian