A new study brings us one step closer to mapping intelligence in the genetic code.
Genome-wide association studies (GWAS) allow scientists to assess whether certain genetic locations are related to specific traits.
GWAS screen the genome of each person in a group that carries a certain trait of interest. This can then be compared with the genomes of people without that trait.
The technique has proven vital for identifying genetic variants (also called single-nucleotide polymorphisms) that appear more often in certain diseases.
Searching for cognitive ability genes
One trait that has proven trickier to pin down is cognitive ability. Although researchers know that intelligence does have a heritable, genetic component, finding its home in the genetic code has been challenging.
Earlier studies that made some effort to get to the bottom of this problem did not produce clear-cut results. Because cognitive ability is likely to be spread across a number of locations in the genome, not having a large enough sample size is one of the reasons that previous studies have had little success.
One of these earlier studies, using just a few thousand participants, was conducted by Todd Lencz, Ph.D., and published last year. His team could only identify a few genetic loci associated with cognitive ability.
Lencz set out to take another look at this problem, heading up a research team from the Feinstein Institute for Medical Research in Manhasset, NY. This time around, 107,207 people were recruited, all of whom were assessed using neuropsychological tests. Their genomes were also screened.
The results were then compared with another database that housed the genomic data of 300,000 people, whose highest level of educational achievement had also been noted. This is considered to be a relatively reliable estimation of cognitive ability.
More detail was gleaned this time; according to the authors, they "were able to identify 70 genomic loci significantly associated with cognition, implicating 350 candidate genes underlying cognitive ability."
The results were published this week in the journal Cell Reports.
New and intriguing overlaps
Deletions and mutations in some of the loci identified by the team have already been associated with certain neuropsychiatric conditions, backing up the reliability of the study.
Interestingly, there was an overlap between cognitive ability loci and longevity: people genetically predisposed to intelligence tended to live longer. Also, a new genetic overlap was found between cognitive ability and the risk of autoimmune diseases, such as eczema, Crohn's disease, rheumatoid arthritis, and celiac disease.
Finding regions of genes responsible for cognitive ability is interesting in its own right, but there are larger implications.
"For the first time, we were able to use genetic information to point us towards specific drugs that might aid in cognitive disorders of the brain, including Alzheimer's disease, schizophrenia, and attention deficit hyperactivity disorder."
Todd Lencz, Ph.D.
Alongside their dive into the genetics behind cognitive ability, the researchers hunted out potential nootropic drug targets, which are receptors that could be activated to enhance cognitive prowess.
They found some candidates worthy of further study. The strongest contender was cinnarizine, a type of calcium channel inhibitor typically prescribed for seasickness.
Another candidate was a glutamate receptor encoded by the GRM3 gene, which has previously been implicated in schizophrenia. In fact, drugs targeting GRM3 have been suggested as a potential treatment, although trials have not had any success to date.
GWAS are becoming more commonplace as processing power expands and research techniques advance. As Lencz says, "The field of genomics is growing by leaps and bounds."
He continues, "Because the number of genes we can discover is a direct function of the sample size available, further research with additional samples is likely to provide even more insight into how our genes play a role in cognitive ability."
Intelligence is a difficult and nebulous trait, and the new findings are likely to be only a small part of the larger genetic landscape. As technology improves and available genetic data increase, the picture will no doubt become clearer.