Association of serotonin transporter gene polymorphism with nicotine dependence: no evidence for an interaction with trait neuroticism

We sought to replicate previous studies reporting a moderating effect of the 5HTT gene on the association between trait neuroticism and smoking behaviour, and extend on this work by including a formal test of this interaction, in a sample of 141 heavy smokers. Nicotine dependence was measured using the Fagerström Test for Nicotine Dependence; trait neuroticism was assessed using the Eysenck Personality Questionnaire. All participants were genotyped for the 5HTT-LPR polymorphism. A 3 × 2 ANOVA of nicotine dependence score, with genotype (L/L, L/S, S/S) and neuroticism (high, low) as between-subjects factors, indicated a significant main effect of genotype (F[2, 135] = 3.13, p < 0.05) in the predicted direction, with the short allele of the 5HTT gene being associated with higher nicotine dependence score. There was a marginal effect of neuroticism (F[1, 135] = 3.01, p = 0.08) in the predicted direction, with high trait neuroticism being associated with higher nicotine dependence score. The interaction effect was non-significant (F < 1). These data suggest that 5HTT genotype is associated with nicotine dependence independently of any association between this gene and trait neuroticism that may modulate smoking behaviour. We failed to replicate the finding of a moderating influence of 5HTT genotype on the association between neuroticism and nicotine dependence.