In the KEGG analysis, DEGs were enriched in the PI3K-Akt signaling pathway, human T-cell leukemia virus 1 infection, the cell cycle, and phagosome in cancer in the training cohort (Figure 4E) and nicotine addiction, coronavirus disease, the ribosome-related pathway, and the neurodegeneration pathway in the validation cohort (Figure 4F, Supplementary Figure S3B). Here, AKT1 is linked to nicotine dependence.