AHRR and post-traumatic stress disorder: DNAm at cg05575921 is one of the strongest and most reliable indicators of smoking in the epigenome [59], but AHRR methylation at this locus, and at other CpG sites within the gene, has also been associated with other phenotypes above and beyond the effects of cigarette smoking, including epigenetic age acceleration (e.g., [60]) and C-reactive protein levels (e.g., [61]), both of which have been linked to PTSD in other recent studies [12].