We have recently found an association between smoking and mental distress in a three year follow up study among Norwegian adolescents. Earlier studies have demonstrated that the serotonin transporter gene interact on the association between negative life events and depression.

The aim of this study is, in stratified analyses by sex, to investigate whether there is a similar interaction of the serotonin transporter genotype on the relationship between smoking and mental distress.

All 10th graders in Oslo in 2000 and 2001 (n=7343, 88%) filled in questionnaires during school classes. The 2001 cohort (n = 3811) constituted the baseline. Of the participants in the baseline study 2489 (65%) participated in the follow-up. The response rate was 58% in boys and 74% in girls. The Hopkin's Symptom Cecklist-10 was used to measure mental distress. At follow up almost all participants provided genetic material using a cyto-brush on the buccal mucosa. The tag SNPs were analysed with Taqman MGB.

There was a significant interaction effect between the different genotype alleles and smoking among girls (F=4.0, p=0.019), but not among boys (F=0.8, p=0.44). Girls that are smoking daily with the long gene allele variant had lower mental distress scores than those with the short allele variant. Those with the heterozygote variant had scores that were between those with the short and long variant.

There is an interaction effect for the serotonin transporter genotype among adolescent girls, but not in boys in the relationship between smoking and mental distress.