flexible epigenetic biomarker of smoking. In total, this review identified seven studies using the 27k platform and a further 23 using the 450k platform. Based on the results of these studies, nine more in-depth investigations of promising loci were identified as part of the third wave of studies. Below, we review loci replicated by 7 or more studies, a cutoff chosen after review of our findings to help limit the scope of discussion. It should also be noted that none of the candidate genes investigated in earlier pyrosequencing have demonstrated replicated associations with smoking in later array-based studies.
