Since the publication of the above array-based, several follow-up studies have gone on to confirm associations between smoking and AHRR and expand findings, often using sequencing or mass spectrometry. These studies once again confirm methylation changes related to prenatal smoking exposure, as measured by cotinine, both in newborns [69], and 18 months later [70]. Two groups combined several loci at AHRR and other genes to determine if combining signals could lead to an improved instrument for assaying smoking exposure status. Shenker and colleagues [71] found that the combination of four CpGs, including cg05575921, provided the best AUC, whereas Philibert and colleagues [72] found cg05575921 to have excellent predictive properties as a single test, with an AUC of 0.99.
