In contrast with our finding, recent genome wide association studies on smoking have found no evidence for association within TTC12-ANKK1-DRD2(3, 6, 48). A plausible explanation for this discrepancy is the difference in age in the conducted studies as compared to our study. In Thorgeirsson et al(3) the mean ages of samples included were older than 50 years. Similarly, in Caporaso et al(48) more than 80% of participants were older than 60 years. According to our results, TTC12-ANKK1-DRD2 effect on smoking decreases from age 14 to age 31 years and might become undetectable at later ages. This result also underlies that more studies conducted in young cohorts are needed. Genes influencing smoking behavior in adolescence are likely to partially differ from genes influencing smoking in adulthood and old age(38) and whole genome association studies in adolescents might therefore enable the discovery of novel risk variants for smoking.
