May 26, 2017

More genes linked to IQ

Because IQ is linked to so much else, psychometricians have long expected it to be polygenetic: Many genes have an input into it.  I have always favoured the view that a high IQ is simply one aspect of general biological good functioning.  The brain is just another organ of the body, after all. So if that is the case, the number of genes linked to IQ should be very large indeed.  So the work below is just a first step.

Various reports of this study distort its results --  with the NYT in the lead on that.  So let me answer them here:

The NYT says: "These genes do not determine intelligence, however. Their combined influence is minuscule".  That is exactly the opposite of what the study found.  I append the journal abstract below so readers can check for themselves.  The authors found that their 52 genes explained 5% of the variance in IQ.  That per cent of variance explained is about normal in psychological research and has been used to support many claims of causality.  And the 5% will rise as more genes are analysed.

Other reports misunderstood the links to Alzheimers and Schizophrenia.  The study found that people with high IQ genes had LESS Alzheimers and Schizophrenia, not more.  It is interesting, however, that high IQ genes are associated with autism.  As is well known, autistic people often have extreme mental abilities in some fields, so the finding is not too surprising.  Most high IQ people are not autistic, however.

I liked the finding that high IQ people are tall, thin and unlikely to smoke. I am an example of that.  I am 5'10", was very skinny in my early life and have never smoked. 5'10" is not that tall these days but when I was born 73 years ago it was. The average male height in Australia has increased 3" in the last 50 years.


Intelligence is one of the most investigated traits in humans, but so far, only a handful of genes have been associated with the trait.

Now, researchers have made a major advance in understanding the genetic underpinnings of intelligence, uncovering 52 genes for the trait, 40 of which are new discoveries.

In particular they found that many people with these genes are more likely to have other traits, including being tall, thin and unlikely to smoke.

Scientists hope the findings could provide new biological insights into brain function and understanding, and help to define the genetic component of IQ.

The findings also turned up a surprising connection between intelligence and autism that could one day help shed light on the condition's origins.

"For the first time, we were able to detect a substantial amount of genetic effects in IQ," said Danielle Posthuma, a researcher at the Center for Neurogenomics and Cognitive Research in Amsterdam, and the main architect of the study. "Our findings provide insight into the biological underpinnings of intelligence," she told AFP.

An international research team led by Vrije Universiteit Amsterdam studied genetic data from over 78,000 individuals. The data included information on DNA genotypes and intelligence scores, which led the team to discover new genes and biological routes for intelligence.

Despite high heritability estimates of 45 per cent in childhood and 80 per cent in adulthood, until now, only a few genes had been associated with. But the new study uncovered 40 new genes, most of which are mainly expressed in brain tissue.

Professor Posthuma said: 'These results are very exciting as they provide very robust associations with intelligence. '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 results showed that people with the genes were more likely to have high educational achievements, and were also likely to be taller, not to smoke, and to have autism spectrum disorder.

In contrast, people with the intelligence genes were less likely to have Alzheimer's disease, depressive symptoms, smoking history, schizophrenia, high body mass index, or obesity.

Dr Suzanne Sniekers, who also worked on the study, said: 'These genetic correlations shed light on common biological pathways for intelligence and other traits.

'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.'

The researchers stress that future studies will be needed to clarify the exact role of these genes in intelligence in order to gain a more complete picture of how genetic differences lead to differences in intelligence.

Professor Posthuma added: 'The current genetic results explain up to five per cent of the total variance in intelligence.

'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.'

SOURCE

Genome-wide association meta-analysis of 78,308 individuals identifies new loci and genes influencing human intelligence

Suzanne Sniekers et al.

Intelligence is associated with important economic and health-related life outcomes1. Despite intelligence having substantial heritability2 (0.54) and a confirmed polygenic nature, initial genetic studies were mostly underpowered3, 4, 5. Here we report a meta-analysis for intelligence of 78,308 individuals. We identify 336 associated SNPs (METAL P < 5 × 10−8) in 18 genomic loci, of which 15 are new. Around half of the SNPs are located inside a gene, implicating 22 genes, of which 11 are new findings. Gene-based analyses identified an additional 30 genes (MAGMA P < 2.73 × 10−6), of which all but one had not been implicated previously. We show that the identified genes are predominantly expressed in brain tissue, and pathway analysis indicates the involvement of genes regulating cell development (MAGMA competitive P = 3.5 × 10−6). Despite the well-known difference in twin-based heratiblity2 for intelligence in childhood (0.45) and adulthood (0.80), we show substantial genetic correlation (rg = 0.89, LD score regression P = 5.4 × 10−29). These findings provide new insight into the genetic architecture of intelligence.

Nature Genetics. (2017) doi:10.1038/ng.3869




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