CHRNA5-CHRNA3-CHRNB4 haplotypes were also associated with age of self-reported smoking cessation in this community-based sample (Wald=8.64, df=2, omnibus-p=0.015). Compared to H1, the high-risk haplotype H3 was associated with a later quit age (RH=0.92, 95%CI=0.86-0.98, df=1, p=0.0088) (Table 1). The median age of smoking cessation was 57 years for those with haplotype H3, and 55 years for those with haplotypes H2 and H1 (Wald=8.46, df=2, omnibus p=0.015 for the overall haplotype effect). The strength of this association was more modest than the association with heaviness of smoking. To further understand this genetic association, we added CPD as a covariate into the model. Smoking a higher number of cigarettes per day was strongly associated with a later quit age (RH=0.63, 95%CI=0.61-0.65, p<1.0×10−8), and the haplotypes were no longer associated with age of cessation (Wald=1.72, df=2, omnibus-p=0.42 for the overall haplotype effect). Analyses were repeated with smoking duration (measured from self-reported age of onset of smoking to age of smoking cessation) as the outcome variable, and similar results were seen.
