The data downloaded from the GWAS Catalog included 14 different studies, in which 2,719 genome-wide significant associations between a SNP and intelligence were reported in total. These studies used a total of 15 samples, and included a combined total of up to 1,651,560 individuals.1
Upon closer inspection, though the GWAS Catalog website lists 18 different studies, only 14 of them are included in the downloaded dataset. The reasons for this appear to be twofold: the paper by Lam et al. (2017)\cite{Lam2017} was counted twice on the Catalog's website, because it measured SNP associations with cognitive ability once with the novel technique of multi-trait analysis of GWAS (MTAG) and once without it, and three studies\cite{Davies2011}\cite{Davis2010}\cite{Butcher2008} were listed on the website but excluded entirely from the downloaded dataset, apparently because all of them reported no genome-wide significant associations whatsoever. Consequently, ignoring the single instance of double counting, this list technically only includes 17 unique studies.
I will be using the total number of 17 studies in most of the remainder of this paper, but when analyzing SNP associations I will only be examining the 14 studies which reported any such associations whatsoever. The titles of all 17 included studies are listed alphabetically by title in Table 1 below.
A three-stage genome-wide association study of general cognitive ability: hunting the small effects. Title |
A combined analysis of genetically correlated traits identifies 187 loci and a role for neurogenesis and myelination in intelligence. |
A genome-wide association study for extremely high intelligence. |
Biological annotation of genetic loci associated with intelligence in a meta-analysis of 87,740 individuals. |
Childhood intelligence is heritable, highly polygenic and associated with FNBP1L. |
Genetic contributions to variation in general cognitive function: a meta-analysis of genome-wide association studies in the CHARGE consortium (N=53949). |
Genome-wide association meta-analysis in 269,867 individuals identifies new genetic and functional links to intelligence. |
Genome-wide association meta-analysis of 78,308 individuals identifies new loci and genes influencing human intelligence. |
Genome-wide association studies establish that human intelligence is highly heritable and polygenic. |
Genome-wide association study of intelligence: additive effects of novel brain expressed genes. |
Genome-wide quantitative trait locus association scan of general cognitive ability using pooled DNA and 500K single nucleotide polymorphism microarrays. |
Genome-wide screening for DNA variants associated with reading and language traits. |
GWAS meta-analysis reveals novel loci and genetic correlates for general cognitive function: a report from the COGENT consortium. |
Large-Scale Cognitive GWAS Meta-Analysis Reveals Tissue-Specific Neural Expression and Potential Nootropic Drug Targets. |
Molecular genetic evidence for overlap between general cognitive ability and risk for schizophrenia: a report from the Cognitive Genomics consorTium (COGENT). |
Results of a "GWAS plus:" general cognitive ability is substantially heritable and massively polygenic. |
Study of 300,486 individuals identifies 148 independent genetic loci influencing general cognitive function. |
Table 1. The 17 unique published studies included in the present review. Papers whose titles are in bold in this table were excluded from association analyses because none of them reported any genome-wide significant associations. The paper whose title is underlined included two sets of associated SNPs and was therefore counted twice in the GWAS Catalog (hereafter "the catalog").
Inconsistent reporting
All of the included SNPs were reported in the catalog using the corresponding NCBI-assigned Reference SNP (rs) number (e.g. rs10010325), with four exceptions: in the catalog, 4 of the 13 SNPs associated with intelligence in the study by Trampush et al. (2017)
\cite{Trampush2017} were listed in the format "chrA:B", where A is the number of the chromosome and B is the position of the SNP on the chromosome. The value in the "location" column for these SNPs in the catalog's page for Trampush et al. is listed as "Mapping not available".
\cite{catalog} For each of these locations, I used NCBI's Genome Data Viewer
\cite{viewer} to examine what is actually at these locations in the genome. The four locations formatted in this way in the catalog are: chr17:43463493 chr17:43569909 chr17:44210933 chr17:4436657