Early array-based studies using the Illumina 27k platform did not identify any association between smoking and AHRR due to lack of coverage of this area. However, among the twenty studies using the 450k platform to test for associations between a wide variety of smoking exposures across varying ages, tissues, ethnicities, and both sexes, only six failed to demonstrate the association between AHRR methylation and smoking. In 11 of those studies, a single probe, cg05575921, was identified as the most associated, and the probe was the second in another [27] and third in yet another [52]. Although significant associations between smoking and other probes in the AHRR region have been reported in a number of studies, in only one [61] were other AHRR probes ranked more highly.
