A massive scientific undertaking involving 60,000 adults and 20,000 children probed the human brain for genes that underpin cognitive skills. The scientists report finding 40 new genes that are one way or another linked to intelligence — the most important contribution any study has made thus far. All in all, the total number of genes involved in human intelligence so-far identified is 52. Someday, these genes could be used to design drugs that make us smarter or treat neurodegenerative diseases like Alzheimer’s or Parkinson’s.
About half of the differences seen in IQ scores can be explained by genetic factors, the rest is influenced by a mix of nutrition, pollution exposure, social setting, education. However, we only know about a handful of genes that code for intelligence out of all the hundreds or possibly thousands of genes there ought to be. Some of these genes instruct neurons to grow, others guide the path these neurons take — thus building synapses.
To look for genetic markers of intelligence across the human population, the team of researchers led by Professor Danielle Posthuma, a statistical geneticist at the Free University of Amsterdam assessed 13 different groups of people of European descent. In total, some 80,000 people were involved who had their intelligence assessed by the “g-factor” — also known as ‘general intelligence’, that refers to the existence of a broad mental capacity that influences performance on cognitive ability measures — rather than IQ.
The researchers then carried out a genome-wide association study (GWAS) that determines connections between a trait and DNA markers called single-nucleotide polymorphisms, or SNPs, which might determine an individual’s likelihood to develop a specific trait. This method enabled the team to identify 336 significant SNPs.
They then turned to yet another similar method called genome-wide gene association analysis (or GWGAS), which this time calculates the effect of multiple SNPs within genes and can identify actual associated genes. Ultimately, 52 genes linked with intelligence were isolated, out of which 12 were previously known to science.
The most important genes — or those that were the strongest linked to intelligence — are involved in regulating the nervous system’s development and cell death. The most significant was the FOXO3 gene, which is involved in insulin signaling and could also trigger apoptosis, the process of programmed cell death that occurs in multicellular organisms. Another strongly associated gene was CSE1L, a gene involved in apoptosis and cell proliferation.
There’s a lot of potential things you can do with this information, from developing drugs that enhance cognition to blueprints for designer babies — both prospects are pretty far fetched at this point. But some uses are already on the horizon such as ranking IVB embryos based on what their genomes say.
The authors of the paper published in Nature Genetics make sure to point out, however, that genetics can only account for so much of a person’s intelligence. It’s not clear at this point whether ‘nature’ counts more than ‘nurture’ as far as grafting intelligence is concerned.