A Quantitative Trait Locus Associated with Cognitive Ability in Children

Quantitative trait loci (QTLs) associated with general cognitive ability (g) were investigated for several groups of children selected for very high or for average cognitive functioning. A DNA marker in the gene for insulin-like growth factor-2 receptor (IGF2R) on Chromosome 6 yielded a significantly greater frequency of a particular form of the gene (allele) in a high-g group (.303; average IQ = 136, N = 51) than in a control group (.156; average IQ = 103, N = 51). This association was replicated in an extremely-high-g group (all estimated IQs > 160, N = 52) as compared with an independent control group (average IQ = 101, N = 50), with allelic frequencies of .340 and .169, respectively. Moreover, a high-mathematics-ability group ( N = 62) and a high-verbal-ability group (N = 51) yielded results that were in the same direction but only marginally significant (p = .06 and .08, respectively).