Association between intelligence quotient and the 5HTTLPR polymorphism of human serotonin transporter coding gene

Association between common intelligence quotient (IQ) and S and L alleles of functional 5HTTLPR polymorphism causing respectively low and high expression of human serotonin transporter coding gene was studied in young (19-35 years, 50 men and 76 women) and older (>55 years, 39 men and 43 women) Caucasian subjects. They were students, scientists, technicians and administrative staff of Novosibirsk State Universities and State Research Institutes of Russian Academy of Sciences. Significant effects of genotype and age, but not gender on IQ were revealed. Higher IQ scores were observed in the S/S genotype carriers compared with the L/S (p<0.002) or L/L (p<0.003) genotype carriers. No effect of the genotype x gender or genotype x age interaction was found. Based on this result, we hypothesized an increased frequency of the S allele in highly educated university group compared with control population. To test this hypothesis the distribution of the alleles and genotypes in the above mentioned academic sample and control population of Caucasian subjects from Dovolnoe village, Novosibirsk region (n=83) was compared. The frequencies of the S allele (43.5%) and the S/S genotype (20.5%) in the academic sample were significantly higher than in the controls (28.2%, p=0.023 for the S allele and 10.1%, p=0.011 for the S/S genotype). The results indicate a significant association between IQ scores and the 5HTTLPR polymorphism, the involvement of serotonergic neuromodulation in cognitive functioning and provide further support for the classification of the S allele and the S/S genotype as associated with cognition.