BACKGROUNDTobacco use is the major risk factor for numerous health problems. However, only 5% of smokers can successfully quit without therapy owing to the highly addictive properties of nicotine. The serotoninergic system may be involved in smoking behavior because nicotine increases brain serotonin secretion, nicotine withdrawal decreases serotonin levels, and a selective serotonin reuptake inhibitor antagonizes the response to nicotine withdrawal. Serotonin transporter (5-HTT) is the most important protein, as it adjusts the serotonin concentration in the synaptic cleft. There is a polymorphism in the upstream regulatory region of the 5-HTT gene, named 5-hydroxytryptamine transporter gene-linked polymorphic region (5-HTTLPR). Compared with the L allele, the S allele of the polymorphism is associated with decreased transcription efficiency of the 5-HTT gene. In this study, we investigated the relationship between this gene polymorphism and smoking behavior in Chinese males.

METHODSPolymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was performed to find 5-HTTLPR gene polymorphisms in 144 smokers and 135 age-matched healthy non-smokers. A questionnaire was completed in all recruited subjects.

RESULTSThe proportion of L/L (15.3% vs 5.2%) and S/L (50.0% vs 33.3%) genotypes was significantly higher in the smokers than that in the non-smokers (chi(2) = 21.9; P < 0.01). The odds ratio (OR) adjusted by age, education, effects of family members and friends who smoke, and alcohol intake was 2.9 (95% CI 1.78 +/- 4.80). In smokers, the number of cigarettes/day (L/L vs S/L vs S/S: 28 +/- 12 vs 20 +/- 8 vs 16 +/- 6, chi(2) = 18.5, P < 0.01), smoking index (L/L vs S/L vs S/S: 561 +/- 446 vs 393 +/- 341 vs 237 +/- 201, chi(2) = 12.5, P < 0.01) and score on the Fagerström test for nicotine dependence (FTND) (L/L vs S/L vs S/S: 7.8 +/- 1.6 vs 6.2 +/- 2.5 vs 3.5 +/- 2.1, chi(2) = 48.3, P < 0.01) were significantly higher in smokers with an L/L or S/L genotype than that in the smokers with the S/S genotype. There were no significant differences in the proportion of starting smoking before 20 years old (P = 0.219) and those who succeeded in quitting smoking for more than 1 month (P = 0.456) between individuals with different 5-HTTLPR genotypes in smokers.

CONCLUSIONS5-HTTLPR polymorphism may be associated with susceptibility to cigarette smoking in Chinese males. The proportion of the L/L and S/L genotype in smokers was higher than that in non-smokers. In smokers, the level of nicotine dependence and resultant cigarettes consumption may be much higher in individuals with an L/L or S/L genotype than those with the S/S genotype.