Still No Genes for Genius

The latest from Molecular Psychiatry:

Although individual differences in intelligence (general cognitive ability) are highly heritable, molecular genetic analyses to date have had limited success in identifying specific loci responsible for its heritability. This study is the first to investigate exome variation in individuals of extremely high intelligence. Under the quantitative genetic model, sampling from the high extreme of the distribution should provide increased power to detect associations. We therefore performed a case–control association analysis with 1409 individuals drawn from the top 0.0003 (IQ >170) of the population distribution of intelligence and 3253 unselected population-based controls. Our analysis focused on putative functional exonic variants assayed on the Illumina HumanExome BeadChip. We did not observe any individual protein-altering variants that are reproducibly associated with extremely high intelligence and within the entire distribution of intelligence. Moreover, no significant associations were found for multiple rare alleles within individual genes. However, analyses using genome-wide similarity between unrelated individuals (genome-wide complex trait analysis) indicate that the genotyped functional protein-altering variation yields a heritability estimate of 17.4% (s.e. 1.7%) based on a liability model. In addition, investigation of nominally significant associations revealed fewer rare alleles associated with extremely high intelligence than would be expected under the null hypothesis. This observation is consistent with the hypothesis that rare functional alleles are more frequently detrimental than beneficial to intelligence.

In English, they could find neither single gene variants clearly associated with genius, nor could they find any groups of variants shared by their genius sample. Because they could not find any such associations, their model says genius is only 17.4% inherited. I doubt that is right, but anyway it seems clear that we have a long way to go to understand the genetics of intelligence.

Attempting to read the article it seems pretty clear that there are no single genes where a big difference between one type and another results in a big increase in intelligence -- no mutant geniuses. All of the weird gene types they identified lead to decreased intelligence. Higher intelligence results from many minor variations adding up.