Three hundred fifteen samples passed quality control with complete data and were included in the analyses (from 49 African, 51 Asian, and 215 European American participants). Multiple factors including population structure principal components, age, sex, BMI, and smoking status were incorporated to model NMR in a genome-wide, multi-ethnic meta-analysis. Adequate Type I error control was observed with genome-wide significant results at CYP2A6 (min p = 9.10E-15). The top SNP accounts for 12 %, 27 %, and 19 % of the NMR variation in European Americans, African Americans, and Asian Americans, respectively. The minimum p-value in the nearby CYP2B6 region was 1.85E-5 with association patterns differing by ancestry (Fig. 2). Association patterns with the NMR remained intact for CYP2B6 in an analysis adjusting for CYP2A6’s top SNP; other CYP2A6 SNPs showed evidence of independent association after this adjustment (min p = 1.71E-7).
