-KL-VS (Science and Technology, 2014) - The KL gene codes for the protein klotho. Specifically the VS variant of the KL gene seems to improve IQ by around 6 points. Three independent studies have confirmed these findings. In one study of 220 volunteers between the ages of 52-85, those with the variant had better cognition.
In order to confirm that their finding was the result of a real causative element between the VS variant and higher IQ, they genetically engineered mice to have the mouse-counterpart of the KL-VS gene, which likewise increases the klotho in their brains. They likewise exhibited higher levels of intelligence.
The brains of the mice possessed abnormalities when examined as well. NMDA receptors in the brains of mice had double the number of GluN2B, a molecular subunit of NMDA receptors associated with higher levels of intelligence.
The following genes were mentioned as accounting for only half a percent of IQ variation:
-HMGA2 (UCLA, 2012) - Specifically, those with the C variant of HMGA2 had larger brains and higher IQs than those with the T variant.
-NPTN (King's College London, 2014) - This gene is believed to affect the thickness of the brain's grey matter, which is correlated with IQ level. Grey matter is involved in attention, perceptual awareness, thinking, memory, consciousness and language. 1,583 teenagers were given IQ tests. Those with one variant tended to have thinner cortices and lower IQs whereas those with another variant tended to have thicker cortices and higher IQs.
Researchers investigated this gene in the brain cells of humans and mice. They believe that the left hemisphere is more sensitive to the effects of mutations of the gene. "Their findings suggest that some differences in intellectual abilities can result from the decreased function of the NPTN gene in particular regions of the left brain hemisphere"(King's College London, 2014)
-ADRB2 (Gosso, 2007) - The beta-2 adrenergic receptor, researchers argue, is responsible for 1% variation in IQ, making it a highly significant source of IQ variation. This polymorphism, they say, is responsible for gene expression of beta-2 adrenergic signaling, which has been shown to be involved in memory consolidation.
This result illustrates the validity of our approach to detect
functional variation and demonstrates for the first time a direct link between
quantitative genetics and the genetics of species differences.
The 3% Solution (2014). Retrieved from: http://www.economist.com/news/science-and-technology/21601809-potent-sou...
University of California, Los Angeles (UCLA), Health Sciences. (2012, April 15). New genes linked to brain size, intelligence. ScienceDaily. Retrieved June 30, 2014 from www.sciencedaily.com/releases/2012/04/120415150123.htm
King's College London. (2014, February 11). Scientists identify gene linking brain structure to intelligence. ScienceDaily. Retrieved June 30, 2014 from www.sciencedaily.com/releases/2014/02/140211084051.htm
Gosso, Maria. COMMON GENETIC VARIANTS UNDERLYING COGNITIVE ABILITY. Retrieved from: http://dare.ubvu.vu.nl/bitstream/handle/1871/11368/7201.pdf?sequence=5