The KEGG pathway analysis of the TCGA (Figure 4C) and CGGA (Supplementary Figure 4C) data indicated that the downregulated DEGs were enriched for neuroactive ligand-receptor interaction, cAMP signal pathway, nicotine addiction, and synaptic vesicle circulation, while the upregulated DEGs were enriched for the PI3K-Akt signal pathway, MAPK signaling pathway, B cell receptor signal pathway, NF kappaB signal pathway, leukocyte transcutaneous migration, cell cycle and T cell receptor signal pathway. Here, AKT1 is linked to nicotine dependence.