Association between smoking habits and tryptophan hydroxylase gene C218A polymorphism among the Japanese population

Genetic polymorphisms have proposed a new insight in smoking behavior. Genes in serotonin system are one of the candidates because of serotonin's role in mood regulation. A polymorphism C218A in intron 7 of the tryptophan hydroxylase (TPH) gene has been hypothesized in relation to smoking predisposition.

We examined the association on two Japanese populations: one was from the first-visit outpatients of Aichi Cancer Center Hospital during 3-month period between April and June, 2001 (N=591), and the second was from the examinees who attended a health checkup program supported by the Nagoya municipal government in 2000 (N=446). Written documents on informed consent were obtained and lifestyle questionnaires were recorded. TPH C218A genotypes were determined by the polymerase chain reaction with confronting two-pair primers (PCR-CTPP) method.

The frequencies of the C- and A-allele were 52% and 48%, respectively, which was in Hardy-Weinberg equilibrium. As for current smoking status, no associations were statistically observed. It was, however, indicated that smokers with A/A genotype started smoking earlier in their life. Among male health examinees, mean ages at starting smoking were 18.7 (A/A), 19.9 (C/A), and 22.4 years (C/C), (P<0.01). Also, on the Aichi Cancer Center Hospital subjects aged 60 and older, mean ages were 19.0 (A/A), 20.2 (C/A), and 20.3 years (C/C) for males and 22.3 (A/A), 31.0 (C/A), and 33.0 years (C/C) for females (P<0.05).

The present study demonstrated that the TPH C218A polymorphism in intron 7 had no association with current smoking status in Japanese population. The hypothesis of early smoking initiation of A/A genotype was partially in agreement.