A total of 40 newly identified genes have been linked to intelligence in one of the largest studies of its kind.
The scale of the discovery is huge. Previously, there were only a handful of genes with a robust link to intelligence. A study published in the journal Nature Genetics has now identified a total of 52 such genes, with 40 of them that had never been linked to intelligence previously.
The study scanned the genomes of almost 80,000 people of European descent, comparing unique variations in the genome with their IQ score. The size of the study was the main factor that helped them pick out the unique variations associated with intelligence reliably.
"I wasn't really expecting to find so many significant genes," study author Danielle Posthuma of Vrije Universiteit Amsterdam told IBTimes UK.
Some of the genes were more strongly associated with intelligence than others, although there were no stand-out genes that were much more strongly linked than the rest, the researchers found. Instead, intelligence appears to be subtly influenced by a very wide range of genes.
Many of the genes involved were involved in brain structure and function.
"Most are involved in regulating cell development. Some specific genes are mostly involved in synaptic function. The majority of genes are mostly expressed in brain tissue – and that's what we would expect with genes associated with intelligence," said Posthuma.
However, several had been known for traits other than intelligence before this study.
"One of the genes I thought was most interesting, was shank3 – that has not been associated with IQ before, but it's a known gene for autism," she said. A link between intelligence and traits for autism has been identified before in other studies, although many people with autism have learning difficulties.
The next steps in the research will be to investigate the functions of these genes further, and to see whether some of the gene variants are expressed in higher levels in the brain in some individuals than others.
"Based on that we can design an over-expression study in brain tissue and see what are the consequences. Maybe their cells morphology are different, or the synaptic function might change," said Posthuma.