Meta-analysis of the per-allele association of rs1051730–rs16969968 genotype on unadjusted self-reported daily cigarette consumption among current smokers indicated strong evidence of association (Figure 1). Pooling the six studies within a random effects framework indicated that the risk allele was associated with increased self-reported cigarette consumption (mean increase in number of cigarettes per day per allele = 1.0 cigarette, 95% CI = 0.57 to 1.43 cigarettes, P = 5.22 × 10−6). The between-study heterogeneity was low and not statistically significant (I2 = 0%, Pheterogeneity = .72). After adjustment for cotinine levels, the per-allele estimate was reduced by 50% (mean increase in number of cigarettes per day per allele = 0.45, 95% CI = 0.05 to 0.86 cigarettes, P = .029). Between-study heterogeneity remained low and was not statistically significant (I2 = 0%, Pheterogeneity = .51). Weak evidence for a difference between the estimates for the unadjusted and adjusted analyses was observed (P = .07) (not shown in the figure).
