With respected to the KEGG pathways of genes with up-methylated m6A peaks, we found that the hyper-methylated mRNAs were enriched in biotin metabolism, morphine addiction, nicotine addiction, aldosterone synthesis and secretion, the PPAR signaling pathway, and the mTOR signaling pathway (Fig. 3c, Additional file 7: Table S7). Here, PPARA is linked to nicotine dependence.