Association of the serotonin transporter gene with smoking behavior.

OBJECTIVE In an ongoing molecular genetic study of temperament, participants were genotyped to examine the association of smoking with two polymorphisms of the serotonin transporter gene (SERT): the promoter region, 5-HTTLPR, and an intronic variable-number-of-tandem-repeats region (VNTR). METHOD Full information was available for 330 families, and 244 "ever smokers" were identified (54 past smokers, 190 current smokers). The average number of cigarettes smoked per day was 13.12, and the mean Fagerstrom Tolerance Questionnaire score was 4.79. Associations of genotype, Tridimensional Personality Questionnaire scores, and smoking phenotype were tested by using a robust family design with a variance-components framework and by case-control analysis. RESULTS There was a significant excess of the 5-HTTLPR long allele with the 12-repeat VNTR in current smokers, past smokers, and ever smokers, compared to participants who had never smoked. The results from the population design were confirmed in the family-based analysis. No association was observed between two quantitative measures of smoking and the polymorphisms. A weak association was observed between novelty seeking and the VNTR polymorphism and between reward and 5-HTTLPR. Smokers, regardless of gender, scored significantly higher on novelty seeking and did not differ on harm avoidance or reward. CONCLUSIONS There was a highly significant association between SERT and the categorical definition of smoking, irrespective of dependence level, suggesting that this gene influences the initiation of smoking. Mediation analysis failed to substantiate the hypothesis that novelty seeking partially mediates the effect of SERT on smoking. SERT appears to independently contribute to novelty seeking and smoking.