Genotyping was performed by the Center for Inherited Disease Research at Johns Hopkins University using the Illumina Omni2.5 microarray (www.illumina.com). Data cleaning was led by the GENEVA Coordinating Center at the University of Washington. Additional CYP2A6 genotyping, and application of the predictive model of CYP2A6 activity, were conducted as previously described (7, 11). The predicted nicotine metabolism metric for all subjects was calculated from CYP2A6 diplotype. Briefly, all analyses of measured metabolism are performed on a metabolism metric, the ratio of deuterated (D2) cotinine / (D2cotinine+ D2nicotine), determined 30 minutes following oral administration of D2nicotine. The original model parameters were derived from the regression, log (1 −metabolism metric) = α + βH1 + βH2 where α is the intercept, H1 represents the first CYP2A6 haplotype, and H2 represents the second CYP2A6 haplotype for each subject. Slow nicotine metabolism function is defined as the lowest quartile of metabolism function as used in previous research on nicotine metabolism(12-14). Based on the distribution of the metabolism metric, the cut point closest to the lowest quartile defines 29.3% of participants with slower metabolism. The frequencies of slow vs. fast metabolizers, stratified by treatment group, are in Table S1 and Figure 2.
