An international research team has uncovered novel genes and new biological routes for intelligence. The findings, reported in the latest issue of the journal Nature Genetics, signify a major advance in understanding the genetic underpinnings of intelligence.
“These results are very exciting as they provide very robust associations with intelligence,” says Danielle Posthuma, a professor at the Vrije Universiteit Amsterdam and principal investigator of the study. “The genes we detect are involved in the regulation of cell development and are specifically important in synapse formation, axon guidance, and neuronal differentiation. These findings for the first time provide clear clues towards the underlying biological mechanisms of intelligence.”
The study relied on a dataset of more than 78,000 individuals with information on DNA genotypes and intelligence scores.
“Individual genetic variants almost always have very small effects,” explains David Cesarini, an associate professor in New York University’s Department of Economics and one of the study’s co-authors. “As a result, large samples, such as the one used in this analysis, are critically important for reliably separating out chance findings from real genetic signals.”
Cesarini was part of a team that examined a set of twins’ genetic make-up and cognitive function.
Intelligence is one of the most investigated traits in humans and higher intelligence is associated with important economic and health-related life outcomes. Despite high heritability estimates of 45 percent in childhood and 80 percent in adulthood, only a handful of genes had previously been associated with intelligence and for most of these genes the findings were not reliable. The study uncovered 52 genes for intelligence, of which 40 were completely new discoveries. Most of these genes are predominantly expressed in brain tissue.
The study also showed that the genetic influences on intelligence are highly correlated with genetic influences on educational attainment, and also, less strongly, with smoking cessation, intracranial volume, head circumference in infancy, autism spectrum disorder, and height. Inverse genetic correlations were found with Alzheimer’s disease, depressive symptoms, smoking history, schizophrenia, waist-to-hip ratio, body mass index, and waist circumference.
“These genetic correlations shed light on common biological pathways for intelligence and other traits,” observes Suzanne Sniekers, first author of the study and postdoctoral fellow in Posthuma’s lab. “Seven genes for intelligence are also associated with schizophrenia; nine genes also with body mass index, and four genes were also associated with obesity. These three traits show a negative correlation with intelligence. So, a variant of gene with a positive effect on intelligence, has a negative effect on schizophrenia, body mass index or obesity.”
Future studies will need to clarify the exact role of these genes in intelligence in order to obtain a more complete picture of how genetic differences lead to differences in intelligence, the scientists say.
“The current genetic results explain up to 5 percent of the total variance in intelligence,” notes Posthuma. “Although this is quite a large amount of variance for a trait as intelligence, there is still a long road to go: given the high heritability of intelligence, many more genetic effects are expected to be important, and these can only be detected in even larger samples.”
Mieke I. Tromp Meesters
Vrije Universiteit Amsterdam