Our meta-analysis also highlighted a locus on chromosome 15, which has consistently been identified in GWAS of smoking quantity. All 279 genome-wide significant variants identified on this chromosome lay within the CHRNA5-A3-B4 nicotinic receptor gene cluster, adjacent genes (IREB2, AGPHD1, PSMA4 and ADAMTS7), or intergenic regions (see Fig. 2). The variant with the lowest p-value (both in this region and overall) was rs10851907 (p = 1.46 × 10−19), located in an intergenic region between CHRNB4 and CHRNA3 (Table 1, Fig. 2). The minor allele (A) was associated with a 0.19 SD increase in cotinine levels, equating to a ~34 ng/ml increase in plasma/serum cotinine (Table 1, Fig. 2). This SNP, which is in LD with rs16969968 (r2 = 0.71), accounted for 1.75% of the variance in cotinine levels.
