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 o r for average cognitive functioning. A DNA marker in the gene for insulin-l ike growth factor-2 receptor (IGF2R) on Chromosome 6 yielded a significantl y greater frequency of a particular form of the gene (allele) in a high-g g roup (.303; average IQ = 136, N = 51) than in a control group (.156, averag e 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 co ntrol group (average IQ = 101, N = 50), with allelic frequencies of .340 an d .169, respectively. Moreover, a high-mathematics-ability group (N = 62) a nd a high-verbal-ability group (N = 51) yielded results that were in the sa me direction but only marginally significant (p = .06 and .08, respectively ).