We followed up the 719 genome-wide significant SNPs by meQTL analyses in order to annotate their potential functional consequence. As smoking is known to induce significant changes in methylation patterns [69], only cotinine-verified current smokers (cotinine≥10ng/ml) were included in the analyses. Several SNPs showed significant association with methylation values of 16 CpG sites located within the target region. The 16 CpG sites overlap with relevant genes, such as members of the cytochrome P450 gene family (CYP2F1 and CYP2A7) and EGLN2. According to CIT, methylation in one CpG site mediate the effect of SNPs on the variance observed in NMR. This CpG site (tagged by cg08551532) is located in DLL3, which is involved in neurogenesis via its role in the Notch signaling pathway [70]. Further, DLL3 has been shown to be silenced by methylation in human hepatocellular carcinoma (HCC), leading to restricted growth of cancer cells [71]. Expression of NOTCH3, encoding for a receptor for DLL3, has been shown to be influenced by cigarette smoke [72]. The potential mechanism how DLL3 may affect nicotine metabolism remains to be determined.
