A third observation from this study is that locus 2 (rs578776 and correlates) shows evidence for involvement in heavy/light smoking. Locus 2 is genome-wide significant in the single-SNP analysis of dichotomous CPD without adjustment for locus 1, with the minor allele elevated in controls (meta-analysis p = 1.38×10−25, OR = 0.78). However the association is much weaker (p = 4.50×10−7, OR = 0.87) in the joint logistic regression model that includes locus 1 and locus 2. One interpretation is that part of the single-SNP association at locus 2 is driven by the effect of locus 1 (perhaps related to the high |D'|). Nevertheless, there is evidence for residual signal at locus 2.
